Why are Drum Brakes Making an EV Comeback?

In the past few years, manufacturers like Volkswagen have started fitting drum brakes to their EVs. It seems curious, but in the chase for dependability, economy, and efficiency, drums are making a renewed case for themselves.
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[@mwp5536]

As motoring journalist, technical writer and long-term spanner wielder, I have to commend your work on this video. Well-written, explained in a manner that appeals to novices and experts alike, and free from technical flaws. Perfect.

[@KenFullman]

There are a few inconsistencies. On the one hand he says that drum brakes are cheaper to produce (and rambles on about the handbrake being the cause for this). He also says that drums are more effective because shoes have a greater surface area than pads yet, he says that manufacturers typically make their brakes larger than they need to be and rely on ABS to keep them in check. He also mentions that rear brakes only provide 33% of the overal braking effort of the car If these factors were all true, where drums are only fitted to one axle, it would make sense to fit them to the front. (Since the front axle doesn't generally have a handbrake and It provides most of the braking power) Brake shoes may have a greater surface area than pads but, since the slave cylinder only operates on one end of the shoe, it is just a small portion of the shoe that contacts the drum. This is a mute point anyhow when he states that the disk brakes are already larger than they need to be He also claims that the cost of replacing a slave cylinder is cheaper than replacing a caliper. Since when did the manufacturer worry about the cost of replacements for the consumer? Even if this was true, this would be negated because the cost of replacing pads (which is required much more frequently than calipers or slave cylinders) is much cheaper than replacing shoes. He also claims that having the dust captive within the drum is an advantage. Would any consumer seriously prefer to have dirt in their braking system, as compared to having a clean braking system? Even motorcycles usually have disk brakes nowadays despite, typically still having a drum that is not used for braking

[@RustOnWheels]

@@KenFullmandust on disks settles on your wheel, dust in drums not so much, so for the dust side, which isn’t relevant for the mfg but just a fun trivial thing, drums may let you skip another wheel clean.

[@TwinCam]

Thank you my friend, that's very kind of you to say :)

[@TwinCam]

Ken, I'm not sure what these inconsistencies are, as you haven't pointed any out. Your first point seems to have no issue mentioned. There is no connection between the braking force of equivalently sized systems and a trend of manufacturers oversizing brakes. The two are separate issues. Your second point makes no sense to me, unless you're referring to the higher initial braking force of drums, in which case you've ignored the rest of the video. The contact patch of the brake shoes is not an issue because drum brakes need to be bedded in. Once bedded in correctly, the contact patch is all around, and I can prove that to you through the video where I refresh my Metro's rear drums. All four shoes have perfectly even wear on both leading and trailing edges. You point about service costs is also misinformed at best, as manufacturers have strived to increase service intervals for decades. Cars are now encouraged to go 20,000 miles between services rather than 1,000 miles all for the sake of reduced cost to the customer, and that's without mentioning all the service-free components that needed servicing in the cars of yesteryear. Your final point ignores the fact of what brakes do - they use friction. Friction ejects dust into the much larger drum. Brake dust has no adverse affect on braking.

[@Trump2Prison]

@@TwinCam I do wonder why abandon regenerative brakes. It's only good down to low speed but instead of dissipating the energy from stopping as heat, put it back into the battery or a super capacitor bank, since it may not always be possible to charge the main battery as quickly as power is available. Use the super capacitor bank as an acceleration reserve since the charge dissipates over a few hours. I imagine cost is why they don't. If the question is "Why doesn't business do ..." the answer is usually "Money."

[@lwilton]

One problem I think not mentioned with drum brakes, is that they become ineffective if they get wet. If you drive a drum brake car through water deep enough to come up to the bottom of the drums, the water will flood into the drums. It is effectively an anti-friction layer between the shoes and the drums. This can also happen if you just drive thru a sheet of very shallow water on the road; the splashing water can get into the drums. This was something you had to be aware of when driving a drum brake car on wet days. Go through a puddle, and you might not stop at the next stop sign or light, and just roll right through the intersection, even with both feet pushing down on the brake pedal. The solution was simple. When you went through a puddle that might cause problems, you gently applied the brakes while still giving power to the engine. This would eventually scrape enough water off the shoes that they started to contact the drum. "Riding the brakes" would then generate heat in the drums and shoes and evaporate the water, and you again had full braking ability. Obviously if you had a brain you stopped riding the brakes once they had dried out.

[@stanley3647]

Another problem is thermal expansion. When heat up - drums expand a little reducing braking power.

[@BS-ql5nl]

You want to ride a motorcycle when the disc brakes get wet and freeze a strange sensation pulling a brake leaver and nothing happens. 🤔

[@operator8014]

Another problem, they will freeze together if you apply them while wet in wintertime. Then you gotta go lay in the snow and smack your drums with a hammer till they're freed.

[@andry4313]

@@BS-ql5nl Drive faster. The heat from the braking friction will make it 10x better. Trust me...

[@abccanada6248]

​@BS-ql5nl I raced road bikes for years. In the wet races you'd have crashes happen and you could do nothing about it if you were behind it because you would have without exaggeration multiple seconds before the rim brakes would scrub enough water off the brake track before they gripped, and then they'd fully lock up.

[@AJ-ln4sm]

I've been a mechanic in North American longer than you have been alive. I see so many rear disc brakes destroyed by corrosion. Thank you, road salt. Whereas rear drum brakes, on smaller cars tend to last nearly the lifetime of the car. Great video!

[@Dat_Sun]

1979 620, still has the original rear drums and hardware. Work perfectly.

[@daveallen7767]

Yes rear drums last much longer than rear disc brakes in Midwestern USA where road salt is liberty applied. I tend to keep a car 8 to 12 years & wish all beware cars had rear drum brakes

[@michaelplunkett8059]

Same deal for coastal FL cars from Salt mist. Just did 4 disc's on Camry with all exposed parts.

[@TexRobNC]

When I first heard drum brakes were making a come back, my immediate thought was, "Oh cool, I bet we can make them MUCH better with new tech"

[@petebusch9069]

What is with you people and your constant obsession with new tech? You do realize this attitude is what forces us to use crappy products that have not provent themselves in the real world, EV's are a perfect example of this. You force this crap down our throats using customers for beta testings only to see product after product fail. How about creating useful tech that works, all you people want is new new new, if its new its got to be good according to you.

[@IsaacShoebottom]

​@@petebusch9069 Next time before you come out swinging have you considered he was using tech as in "technology" as in newer engineering advancements in computer aided design, advancements in metallurgy and higher precision manufacturing.

[@petebusch9069]

@@IsaacShoebottom No because thats not what he was talking about. He wanted a new toy because his old one didn't live up to the hype.

[@Zosu22]

⁠@@petebusch9069 No, that really was what they were talking about. I don’t know why you’re insisting that they meant something else and being generally demeaning. Please try not being so hostile to others.

[@petebusch9069]

@@Zosu22 Because your just wrong, it is what he meant and it needed to be called out. Why are you telling me to not be hostile to others? I'm flat out sick of them and their stupid behavior that creates a crappy world for all of us to live in. Its people like you that promote stupidity when you should be calling it out verses defending it. Your dam right I'm being hostile, actually I'm holding back.

[@nigelrg1]

Rather than an additional, small drum brake, my old Acura Integra simply added a worm gear to the handbrake cable, thus multiplying the force many times and allowing the rear discs to be used for the handbrake. It worked well and I wonder why other cars didn't use it.

[@ShortArmOfGod]

Because it encouraged handbrake turns that eventually lead to the cable snapping prematurely.

[@ww6156]

I'm sure my old Suzuki Swift had that, you had to turn the rear piston in order to change the pads

[@alexmcnabb7957]

My Integra was the same. The handbrake cable pulls on a cam on the back of the rear caliper. I'm not sure exactly how it worked internally but it wasn't super reliable. Neither handbrake worked when I bought the car and replaced the calipers, and one of the new ones died within two years. My Acura RSX had the same problem, only one side ebrake working with no visible failures on the outside of the calipers.

[@TheDimking]

Driving a 8th gen civic, never had a problem with the handbrake

[@skonky]

@@ShortArmOfGodyou can still do handbrake turns with a drum brake, i can confirm first hand

[@Dirt-Diggler]

The strange pedal feel you mention is the self servo effect of the shoes, they basically suck themselves to the drum surface, it only affects the leading shoe not the trailing shoe. Really good drum systems have twin leading shoes although that requires 2 single sided slave cylinders per drum or an overly complicated pivot system 👍

[@PaulG.x]

Motorcycles had up to 8 leading shoe front brakes and there were even 10LS ones made

[@Dirt-Diggler]

@@PaulG.x yup 👍 it's just something you get used to and preferable on non servo systems like older cars and bikes 👍

[@lenrichardson7349]

And twin leading shoe designs are rubbish when going backwards or parked on hills nose up.

[@johndavidwolf4239]

VW vans [microbus] had twin trailing drum brakes 50 years ago.

[@vaalrus]

You want complcated, take apart a Lucas-Girling system with the parking brake. Lots of head scratching the first time I had to adjust one of those.

[@rogerf3622]

As someone who has driven many cars in the 60’s with drum brakes, I can tell you with absolute certainty that drum brakes cease to work when driven in very heavy rain or deep puddles. It is not just fade, it is loss of brakes. The only way to get back the braking is to “ride” the brakes for quite some time to generate enough heat to dry them out. They are dangerous period. Also the complicated design of the 3 unique springs combined with the left and right side being mirror images of each other, allows for mechanics to assemble them wrong. Also note that when the brakes are installed, they are adjusted to intentionally “drag” on the drum so to allow them to self-adjust when backing up. I seriously doubt manufacturers would risk the liability that comes from drum brakes.

[@TwinCam]

Hence why you're trained to dry your brakes after driving through standing water.

[@user-oi2rd8yl2u]

Excellent presentation. In an empty German parking lot of a mall in 1968 I was told on how to quickly stop in transversal position my small, rear engine Fiat 850 by abruptly turning the steering wheel to the left whilst pulling the drum handbrake with the right hand. After two or three trials a security guard turned up out of nowhere and asked us to stop.

[@TwinCam]

Thanks mate :)

[@RossReedstrom]

The 850 spider! I grew up with one of those in Minnesota, of all places. Easiest clutch job ever: 850 was the engine displacement in cc, so sub liter. There are larger motorcycles. And since it predated the 5 mph bumper, and was rear mounted, you unbolt the rear panel of the car, push a wheelbarrow under the now fully exposed engine, and unbolt it from the transmission, dropping the engine into the wheelbarrow and take it away, exposing the clutch plates. Replace and reverse. 2 hour job, tops, all you need is a socket set.

[@Surestick88]

They're not the best option on a performance car (though there are some gorgeous finned drum brakes on early 60's F1 cars that at least win some style points) but for the rear wheels on anything non-performance oriented they make a lot of sense. Low wear, low maintenance, and protected from road spray by design. I can see why they make sense for an EV with regen.

[@johnarnold893]

My Chevy 3/4 ton has the original disk brakes on the rear with 276000 k on them. I will soon have to change the pads though.

[@thoubias]

​@@johnarnold893 Issue with EVs is not how long they will last, but how they endure how little they get used. My friend has a hybrid vehicle, and has to fight rusty disks as the car practically never engages the actual brakes if not driven like a maniac. The mandatory yearly roadworthiness inspection we have here does not accept rusty brake disks. So enclosed drum brakes would be a good solution for not having to service the brakes yearly juat because of the car not using them, especially for the conditions here.

[@sammiecaisley]

Formula Vee still use drum brakes today on there 1200cc race cars. One of the main advantages is that the spring pulls the brake shoe away from the drum helping to reduce rolling resistance.

[@tomclanys]

low maintenance on drum brakes is funny, they're the first thing to stop working and completely cease to exist from rust, because of no one noticing the wear. At least with a disk you can notice something's wrong

[@jonaathansimons7938]

60s Buicks also had the lightweight aluminum finned drums. Weekend warrior drag racers have used drum/drum brakes for the reduced rolling resistance for years.

[@justsomejoe3632]

Very interesting! I literally just changed the rear brakes on my wife's hybrid vehicle, mostly because the discs were thoroughly rusted from lack of use. Personally, I'll still take discs over drums, if only to avoid the hassle of removing a drum that's locked onto the shoes because of wear and that little outer ridge of rust that always forms. If I never have to hammer a drum off the shows again it'll be too soon!

[@ktodd4883]

Back off the adjustor prior to removing the drum

[@rogerphelps9939]

I remember doing that on my Morris Minor years ago.@@ktodd4883

[@jessicaandtrains7768]

The corrosion comes off after the first bit of braking. Drum brakes are a step backwards. I'm sure this regen tech can't make up for constantly hauling a very heavy battery around and wasting energy trying to store energy.

[@grahamwoodier5066]

Sadly that isn't the case with rear discs on an EV. With so little use the disc surface becomes very pitted which leads to premature replacement even though they are barely worn. Still I suppose this gives the garage trade something to do.@@jessicaandtrains7768

[@drradar]

​@@jessicaandtrains7768anyone who has ever driven in the mountains or even mildly hilly terrain can tell you just how much better regen is than braking.

[@phils866]

I never thought I'd find a video on drum brakes so interesting, but I did. You have a knack of explaining technical phenomena in a very easy to understand and interesting manner. Technical college tutors take note! ;-) I would like to mention one other 'advantage' of rear drum brakes, and that is the handbrake turn! The fun I had as a youth, in empty carparks and the like, in snowy or wet conditions, using the wand. ;-) Actually, a use of the manual handbrake can get you out of bother in snow. Something modern electronic parking brakes are incapable of.

[@AndrewTSq]

Best is hydraulic handbrake on rear disc brakes, just like rally cars use.

[@davidspendlove5900]

@@AndrewTSqI don’t think handbrake turns are really relevant to everyday driving.

[@AndrewTSq]

@@davidspendlove5900 its good if your front gets loose in the snow, you grab the handbrake to stop the understeer. But normal drivers these days seems more interested in selfdriving cars than driving themself :)

[@franka2507]

Brake lag and unsprung weight is the downside of drum brakes, on large vehicles is more noticeable even more so with abs.😮

[@Summers-lad]

In a RWD car (or in FWD cars with the handbrake acting on the front wheels), if one wheel is spinning on snow or mud, holding the handbrake half on stops the spinning and lets the other wheel grip, so you get moving.

[@paulscountrygarage9180]

Fantastic explanation Ed. I have a 1953 Vauxhall Velox and a 1954 Rover P4 90, both with 4 wheel drums. It is interesting to compare these two systems. The Vauxhall uses leading/trailing shoes on all 4 wheels and you really know you are pushing the pedal, I change down a gear to use engine braking to assist. The Rover, on the other hand has twin leading shoes on the front and leading/trailing on the rear and pedal pressure is GREATLY reduced. So much lighter, in fact, I had to check a booster had not been fitted, it hasn’t. I still use the gearbox to assist with braking, particularly, down hill. Like a lot of ‘old’ technology, drum brakes are much maligned due to the effect of advertising to promote the ‘new’ technologies.

[@neil1997]

Does the rover have a split hydraulic circuit? Ir one circuit works the upper cylinder on all 4 wheels and the other circuit the lower cylinders on the front?

[@paulscountrygarage9180]

@@neil1997 being from 1954 it is a single circuit system. It fails they all fail.

[@alexlail7481]

I'm not sure what the European requirements are but I know that dual circuit brakes became mandatory for new cars in 1968 for US market and I think functionally they were standard for 1967. My daily driver is a 1st generation Ford Bronco with four wheel drum brakes and I can tell you from experience that the material used in the brake lining makes a huge difference on the drive ability and pedal feel. Most of the shoes available now are bonded linings and semi-metallic composition they are grabby and cause the vehicle to dart dangerously for use on the front wheels, there's a limited quantity of organic/ old style composition riveted linings available online as close-out/overstock shoes while they're slightly less effective at decreasing the stopping distance they stop straight and dont grab. Making them mucj safer to use...

[@derekhobbs1102]

@@alexlail7481 I still have asbestos brake pads and linings in my 83 Datsun, thanks to my first boss having some old stock on the shelf. Work much better than modern pads in same system.

[@veden3383]

@@derekhobbs1102 Healthy. Throw them out imo

[@Indy_at_the_beach]

I am subscribing because of your superb use of the language and your brilliant explanations of technical issues. All your teachers should be proud of you.

[@TwinCam]

Thanks mate, that's very kind of you.

[@rsc9520]

I FULLY agree. This is an excellent presentation !!! Very well thought out arguments. Very good delivery!!! Glad to subscribe ....

[@catherinegrimes2308]

I read an article in 1975 in which somebody said that drum brakes could be making a comeback because disc brakes never fully disengage and they introduce friction when the car is moving. It is good to hear that this prediction could eventually be coming true.

[@sjb3460]

I have been fixing our brakes for 40 years, and I think it would be easy to introduce a redesigned disc brake system to keep the pads from rubbing, something along the lines of a couple of springs impinging on a tab to maintain pad separation.

[@906MediaProductions]

​@@sjb3460the Prius uses springed pads, they pull the pads back when not applied, I think it's more common on hybrids.

[@BigUriel]

If the brake components are all in good condition the pads are just gently touching the discs, they cause practically no friction at all. The very principle of operation of disk brakes ensures this, when there's no hydraulic pressure the pistons move freely so any contact with the disc creates a normal force that pushes the pad away.

[@omurize2007]

@@sjb3460should be very easy, all disc brakes in bicycles have springs on the pads to fully separate them

[@zimzim7]

If they don't rub then they won't clean off the discs, so your first stop you would need an entire revolution before the corrosion is off the disc

[@johnscaramis2515]

I'm using my car mostly on long range (200km), driving usually with not much of traffic and looking what lies ahead. Hence not much braking. On my previous car, it was the rear brakes which I had to change first at 90,000 km due to corrosion of the discs, the car would not pass the safety check otherwise. The front brakes were changed at about 120,000km and would have lasted maybe 125-130000 km. Considering the above, I have no issues with the drum brakes on my Cupra Born.

[@ptonpc]

Who else remembers drum brakes sticking on after the car had been left for a while (sometimes overnight depending on weather conditions)?

[@Cyberdyne-kg8ku]

The drums on my SEAT Mini would often stick after I washed it, resulting in the car dragging its rear wheels until they freed up with a loud clonk.

[@ptonpc]

@@Cyberdyne-kg8ku Happy days! Where I lived at the time, it was damp a lot. I had to carry a hammer to give the drum brakes of my Astra a whack so I could move in the morning.

[@hishamg]

We had rear drum brakes on our 2010 VW Polo, last summer we went away on holiday for 2 weeks, and when we got back they had completely seized up. I tried driving it down the road and I was literally dragging the back wheels. Fortunately when I stopped the brakes freed up. We traded the car in not long after.

[@TwinCam]

Handbrake problem, usually. Tends to be due to a lack of copper grease.

[@Low760]

​@@TwinCamno, the OEM doesn't recommend using grease in the brakes.

[@JamesKonopasek-so2qf]

I’m a big car guy and have been following your videos for some time. I watch many motoring videos but have never seen such an informative video on drum brakes. I didn’t think it would be as interesting as it is. Well done :).

[@TheOracle65]

An excellent descriptive video, Ed! One of the best explanations and competitive assessment of hydraulics and the new electric systems. Your delivery is very natural, you’d never think you had a script. Do ignition systems next! Happy Christmas!

[@TwinCam]

Thanks mate :)

[@colinreid7305]

Drum brakes may well have a use in electric vehicles if the heat in the friction material and the drum is carefully controlled using expensive monitoring systems. Drum brakes are more prone to brake fade due to heat build-up and water entering the drum and of course glazing of the friction material and the drum. Drum brakes suffer from leaking wheel cylinders resulting in possible replacement of the brake shoes and also suffer from seized brake adjusters. Drum brakes require continuous adjustment for safety reasons. Disc brakes are cheaper to repair due to the reduced labour requirements more so when changing pads. As a qualified mechanic I would never choose drum brakes over disc brakes on an ICE vehicle but as you say electric vehicles may be a different matter.

[@bobphillips2188]

Speaking as a motor mechanic working from the 60s to the early noughties, drum brakes always required more work (than discs/callipers), new seals more often than ever disc callipers needed, and new cylinders as often as new seals. Scored rear wheel cylinder bores were common (because whereas new brake fluid should have been a service item, it rarely was, and poor practice re-fluid topping up led to dirt in the system) and yet I remember rarely changing seals within callipers. I applaud your bigging up of old-school stuff - at your tender years I was the same, but I am getting on now - and I can see some advantages to drum brakes on the rear end of some less weighty cars. Last thing though - it was always more common to suffer brake pedal flutter with drums than discs. Once out of kilter, drums tend to become worse with use rather than better. Discs aren't perfect, but they work a whole lot better than drums, and with modern manufacturing methods, disc brakes are no more expensive to produce than drums. Ten out of ten for defending drum brakes, but no, never better than discs!

[@timfreeman2603]

The most popular car sold in Australia are utes (small pickup trucks) 90% of which are sold with drum brakes.

[@peddler931]

I remember the Trans-Am racing series - box stock Camaro/Firebirds racing a circuit course with their rear drum brakes. By lap 10 out of 12, they started to go straight off the track in the corners.

[@philipoakley5498]

The one hassle with self maintained drum brakes was that the shoes wore a groove in the drum and the drum edge rusted, so you had a bugger of a job for releasing the shoes enough to get the shoe to clear the edge/rust band! The joys! (And you try telling that to the kids today; and they won't believe you ;-)

[@denniselvy3528]

You are right they are not as reliable as disks, a lot more maintenance. That's why they are on the back they are only about 30% of the breaking force

[@mikefarrington7141]

@@denniselvy3528 ...and in an EV, would be engaged much less frequently (hardly ever unless you're the type to always hard-brake at every stop light). Such wear and tear issues may never arise on a commuter EV. They really do make sense on non-sporty EVs. It'll just be a matter of getting the public to accept that disc brakes aren't the necessity they may believe them to be.

[@LilOleTinyMe]

Funnily enough , another problem with the drums is the manufacturing. More fiddly bits on the brakes for tms to mess up while handling. With the rotor and caliper all you have to worry about is the brake pads falling out which is easy to catch

[@janicewatts5888]

Every 20 k whip the drums off, whip out your angle grinder and grid off the lip.

[@BS-ql5nl]

​@@janicewatts5888 exactly while your there hoover out the dust. It made a big difference when automatic adjustment came out instead of using the square brake shoe adjustment spanner.

[@49commander]

Great Video!! I had not thought about what you said but it makes total sense! I have a 1949 Studebaker Commander Sedan and it still has its Original drums!!! Old cars had smaller brakes because larger brakes were pointless because the tire adhesion was so poor in the pre-radial tire days and modern rubber compounds all bigger brakes did was lock up the wheels even easier!

[@TwinCam]

Yep, it's an amazing turnaround to see such huge brakes on many modern cars!

[@haizi7179]

I literally can't even explain how useful and informative and amazing video this is. Especially since i barely started working with EVs last week. Well done

[@technologytom]

Excellent. Spot on delivery and clarity of explanation. A great example of how engineers have to look back or they might miss a trick.

[@FlameFighterSB]

a phenomenal video. very informative. no fillers and just a patreon ad at the very end

[@jimmys6566]

Brilliant tutorial. I studied applied mechanical engineering in the 1970s and have never heard a better basic explanation than this

[@Simon-nx1sc]

It’s been a while since a single video gave me so many new insights, thank you!

[@TwinCam]

Thanks Simon, that’s very kind of you.

[@wrth]

Braking force being greater is the reason some cars have both disc and drum brakes on the rear axle where the drums are used as a parking brake.

[@GBOAC]

If they are just used as a parking brake I would rather assume they are used to prevent the parking brake scenario affecting the disc brakes, not because of a difference in braking force. Which is a minute requirement anyway when functioning as a parking brake.

[@petergodfrey3439]

Hello, nice video, but you miss a massive point that so many others do. Drum brakes are self servo, meaning that you don’t need power assistance to anything like the degree of a Disk system. Meaning also that you will never have brake failure due to loss of vacuum. Also has a handbrake, it is far less likely to lose its hold, as it is self servo and works if you are parking up or down a hill. I have never had a problem with grabbing by the way either. I hope this is helpful. As usual most of the video otherwise was excellent. .

[@raftonpounder6696]

Disc brakes were first used on aircraft.

[@jensenhealey907efi]

Well done. Very nicely explained.

[@TwinCam]

Thanks mate :)

[@philtucker1224]

Nice one Ed, that article was well worthwhile. I agree with you about having drums on the back being a more sensible option for daily driving. Have a nice Christmas buddy! 🎅🏼👍

[@TwinCam]

Thanks Phil, you too :)

[@MrSamPhoenix]

Love this video! Would love more “car tech explained” videos like this.

[@timkis64]

i drove 18 wheelers in the mountains for many years.i never had an issue with air brake drums. ALLWAYS made sure they were adjusted properly.& used them wisely.once you heat them up to a certain point they fade BADLY.& dont cool back down quickly either.i was aware of it & never had a problem in 15 years.

[@jeremywilliams5107]

Did any of your trucks have retarders fitted?

[@davidw6469]

This is an excellent and thoroughly interesting documentary. Great work.

[@TwinCam]

Ta la.

[@fossilfish786]

You my man are a good teacher. So simple and to the point. Love it. I know 4x4 love drums over discs as they don't warp when going through water

[@highdownmartin]

They don’t work for the next ten miles though

[@allanhugh2044]

@@highdownmartin I wouldn't quite put it at 16 kilometres before they start working again. Possibly after one braking application and certainly after the second braking application you've pretty much gotten your brakes back. This is in a 7500kg 4x4 Isuzu NPS truck, which is fitted with drums all round. Yesterday I was in a state park (Australia) and did a river crossing where the drums went under, it was 500mm to 700mm deep, (bit hard to judge peering out the window) climbed up the bank then when levelled out, applied the brakes, stopped to let water run out and off. Took off to get some speed up, then after a second application, they were working, then onto the next crossing. In another life and riding my near new BMW R90S motorcycle 48 years ago, I did a river crossing and the discs on the front wheel had cracks appearing between the ventilation holes the next morning. I replaced the stainless (?) steel front discs with solid cast iron ones without ventilation holes and they stayed on the bike until I sold it about 115,000 km's later.

[@highdownmartin]

@@allanhugh2044 I saturated my Landy playing in a new forest Ford. It was a good five miles before it stopped/ stopped slewing. So depends on the vehicle I think, mine gets wet brakes driving through big puddles!

[@TwinCam]

Thanks mate, that's very kind of you to say :)

[@allanhugh2044]

@@highdownmartin I suppose it could to an extent, be vehicle specific. I started driving Land Rovers in 1968/9 in the Australian Army, SWB and LWB. The trick we had after a water crossing, was to keep driving (usually in second gear) and apply the brakes with the left foot for a short time to dry them out. Stopping after a crossing was not a good idea, as one could find the following vehicle doing a close inspection of your rear end. I don't really remember having much difficulty with wet shoes not stopping those Land Rovers. Then again the speeds we were travelling at back then weren't much, even on bitumen. 😊 Slewing, hadn't thought of that, but I do remember the slop in the steering box of those Land Rovers being so loose that anything much over 70 km/h in a SWB and you would have difficulty keeping it in a straight line; slewing indeed! Thinking a bit more about slewing, the Land Rovers I drove were all fitted with Uni-Directional Bar Tread tyres, if a bitumen road even looked wet, you needed to have your wits about you as you were generally only one bend away from sliding off the road.

[@dadgarage7966]

This was exceptionally well done. You explain how we got from there to here with drum brakes in refreshingly nuanced way. People who live in places with steep terrain really appreciate rear drum brakes with strong, reliable parking levers.

[@AnalogueGround]

Superbly presented and explained. Things are never as simple as most people want to see them and there’s a shortage of information laid out like this on many subjects.

[@richardbell7678]

The funny thing is that the 'grabbiness' of drum brakes is not a bug, but a feature. The 'grabbiness' is a result of drum brakes being 'self-energizing'-- the geometry of the linkages and shoes means that coming into contact with drum forces the shoe into the drum. The linkages of the two shoes are mirrored so that one of the shoes will be forced into full engagement, regardless of the direction of rotation. The opposite shoe can still be forced into engagement. Heavy vehicles still use drum brakes, for this reason-- you can generate large braking forces, without large pedal forces. In fact, I had assumed that a big reason for a return of drum brakes to EVs was due to the issue of generating large braking forces, while lacking a means of boosting that is not also a parasitic draw on total range. Otto cycle ICE passenger vehicles use the partial vacuum of the throttle body to use atmospheric pressure to increase the force applied to the master cylinder (Diesel passenger vehicles may actually have an auxiliary vacuum pump to supply the brake booster). A happy coincidence is that taking your foot off of the gas to stomp the brake pedal closes the throttle, further dropping the pressure in the throttle body for added boost. Applying the brakes, while the engine is not running, so there is no boost, can be exciting, depending on the vagaries of vehicle mass and driver leg strength. Unboosted drum brakes are much better than unboosted disk brakes. EVs only need mechanical braking at low speeds, when regenerative braking is less effective, or when the vehicles needs to apply large braking forces RIGHT NOW! Most EV service braking is done in the electric motor, so drum braking systems really do make more sense. Anti-lock drum rear brakes were an option on the 1976 Ford Thunderbird (You did not absolutely need them during a panic braking episode, but not having to worry fish-tailing during a sudden stop would add great piece of mind), so the 'grabbiness' of brake drums is a solved problem.

[@TwinCam]

Absolutely, in some cases, but in performance cars, the grabbiness traditionally led to lock-ups and an inconsistent pedal feel, hence why performance cars were the first to make the switch to discs!

[@the_expidition427]

Positive breaking coefficient

[@noobulon4334]

Older hybrids (like my 2nd gen prius) have a small auxiliary vacuum pump to operate the brake booster while the engine isn't running, but newer evs and even some ice driven cars use an electric brake booster for the hydraulic brakes

[@leftyeh6495]

You missed the part where manufacturers have been using hydraulic assist rather than vacuum for years. Generally they run it off the power steering pump. Guess what EV's have? An electric power steering pump 😂 If GM figured out how to do it 30 years ago, I'm going to guess everyone else knows it's out there.

[@jamesellsworth9673]

Thank you for providing an interesting analysis of two types of braking systems.

[@TwinCam]

Thanks James :)

[@unclemarksdiyauto]

Great video and topic! Very easy for everyone to follow. You kept my interest right to the end! Keep up the good work. (And hello from Manitoba, Canada)

[@Mafuskas]

This was a very interesting video. Thank you KZbin for bringing me to your channel. I really enjoyed your style and quality of presentation.

[@GentilsGarage]

Excellent video Ed. Well explained, clear and concise.

[@TwinCam]

Thank you my friend :)

[@usuallyfixingtinkering]

There are some extremely good points made in this video and many are widely known pros and cons with both Drums and Discs. A point to consider is some manufacturers have indeed started manufacturing Drum brakes at the rear. Why? Because they're cheap, cheap, cheap. That is the aim of the game now in the car world, how cheap can they make components without any issues in the first 5 years of ownership, just a little longer than the length of a lease deal. The biggest problem of Drums is thermal expansion of the Drum when hot, bringing the surface further away from the Shoe when most probably you need to use the brakes. However as you've correctly stated there are many advantages. My issue is surely manufacturers were looking at this decades ago before Discs became almost a must-have feature to sell a car. If they decided that Discs were inferior, we would not have them today, and Disc Brake technology has advanced enormously as well. Lastly, even though EV's have to pedals, most are single-pedal driving in most conditions unless an emergency stop, I wouldn't want Drums to be involved in that set-up plus there's the maintenance, Discs are easy, quicker to service. Drums are just horrible to service, take longer for most people and the adjusters are usually never working. Some serious reverse-engineering would have to take place.

[@TwinCam]

The point is of course, when haven't everyday cars been designed to be cheap?

[@Low760]

Yet Chinese utes use discs when Thai utes use drums.

[@Chris_1024_]

Your serivce point is completely irrelevant, as VW says the drums last a lifetime and have no service at all. Disk brakes, despite nearly not used, have to be replaced because of rust. They get very rarely used anyway so heat is also absolutely not a problem. Actually, if brakes not working is your concern, Teslas actually had massive problems with discs as they where not used at all in every day driving, making them rust in 14 days that they couldn't be trusted anymore in an emergency. They solved the problem by deactivaating the regen once a week to grind down the accumulated rust in normal driving to stop them being a titanic safety risc. . If you do not drive track, drum brakes are by far safer themn disc and more reliable. But overheating is mainly a problem on racetracks and driving down a mountain. If you dump the potential energy f.E. of being on a 1900m Mountain into the brakes, that is an extreme amount of heat that definitly rerquire high thermal energy dissipation capability. But that most important use case is totally absent in BEV. There is a nice trip report from a swiss guy making a big tour through swiss alps with his ID.3. ("Mit dem VW ID.3 auf der E-Grand Tour of Switzerland - rein elektrisch in den Alpen",Hans Fischer technikblog ch) He went to the Gotthardpass, 2107m above sealevel. At the highest point, he had just 26km of range left. So he drove 40km downhill to the ionity chargers at Erstfeld, 6472, switzerland, at about 475m above sea level. He arrived with 119km range. Estimating the ID.3's weight was (with driver and stuff) 1980kg, and altitude difference of 1632m, on top of the gotthard, he had about 8,8kWh of potential energy in reference to the charging station at the bottom. That is a lot of energy to dump into brakes as heat. One Golf brake disk (normal one's not high performance) weight 2,7kg each. So 4 of them are 10,8kg. Steel has a heat coefficient of 477J/kg*K or 0,0001325kWh/kgK. So 8,8kWh will heat up 10,8kg of steel to 6100°C, if no heat would be given to the air (Which of course happens a lot, and heat is also transfered to the rims). Drum brakes where a problem in that use case, as they do not get rid of that heat as good as discs.. But the drum break of the ID.3 will see no heat energy at all, as the ID.3 has about 75kW of regen capacity, which is far more than enough to keep the speed low downhill and charge the battery instead of wasting energy by heating up brake disks. As the most important problem of disk breaks, having less air cooling capacity than disks, is totally absent on BEV, Drum breaks are clearly the very best choice for BEV. Drum breaks are also not as powerful as disk breaks and loose braking power when they heat up. But in the case of the ID.3, the drum brakes are used in combination with the regen, so in unison, drum+75kWh of braking power of regen is also eliminating that disadvantage. For a car not used in racing or on the track, it's absolutely idiotic to not go for drum brakes on BEV.

[@usuallyfixingtinkering]

@@TwinCam Looking at the cheapness and build quality of the current generation of cars. They make an 80s Escort look like a battle tank!

[@usuallyfixingtinkering]

@@Chris_1024_ Very good points made here. In fairness I forgot newer cars are not lasting more than 10 years so on that basis they probably don't need looking at - on the basis of age not use alone. But... rust on brake discs only becomes a problem after not using a car for a few weeks at least which causes pitting. Even cheaper brake discs don't pit unless stood for a couple of weeks (having more than one car not being used for a few weeks at a time myself). I doubt it would rust quicker than that unless made of monkey metal. My experience is totallybtue opposite. On paper Drums make more sense, in the real world its debatable. It'll be interesting to see if this develops.

[@prjndigo]

The way you eliminate the disadvantages of a drum brake is simple... you use a mechanical cam system that applies the trailing edge of both pads. Something we've had for a long long long time but it costs 5 more parts... and is STILL cheaper than disks. If you build a set of drums to the diameter that most disks are made at today you end up with a superior system that can use 3 or 5 pads internally with a cam ring application. This leaves the only actual disadvantage that drums have ever had: having to slam on them when backing up to adjust them.

[@David_H-73]

Wow Edd, over quarter million views on a video talking about drum brakes. That speaks volumes about you😊.

[@paulferraby1202]

A very well presented and informative piece. Just one small correction: the ultimate braking force is not provided by the surface area. The surface area affects how much heat the friction surface can handle and how much it wears but the force comes from the geometry. The main factor is the effective radius that the friction acts at. The effective radius of a drum is at the braking surface on the inside of the drum which is quite close to the outside diameter of the brake. The effective radius of a disc brake is somewhere near the centre of the brake pad, which is much smaller. In addition, there is a 'self servo' effect on one of the shoes in a drum brake where the rotation of the drum cobines with the force from the piston to push the shoe even more into the drum which is why the force increases exponentially and grabs.

[@kenbrown2808]

surface area, pressure, and the length of the lever the brake is acting on are all factors in braking force. that is why you use your whole hand to grip a rope and not just your thumb and finger.

[@paulferraby1202]

@kenbrown2808 area does not directly affect the braking force. Don't take my word for it, look it up on Google to see that surface area has no effect on friction force. If you take a drum brake and halve the width of the shoes, the output force for a given pedal effort would be unchanged. Halving the width, and therefore the area, does increase the surface pressure which would dramatically increase wear and fade with the heat dissipated over a smaller area. The reason why you grip a rope with your whole hand is to increase the force by employing more muscles. The increase in area also reduces the contact pressure so your hand doesn't hurt as much.

[@fhwolthuis]

Great video, Ed. In the USA, they use electric drum brakes on trailers, that might be an interesting concept if the force can be modulated electronically, in combination with ABS of course

[@sssxxxttt]

I can only speculate skipping a hydraulic system in cars would make production cheaper

[@Low760]

Trucks and trailers in Europe and Australia use disc brakes on trailers, with ebs. There's still trailers with drums, but discs are lower maintenance, better braking, longer lasting and properly self adjusting. Unfortunately drums coming back isn't great as a mechanic.

[@TheBeingReal]

@@Low760Discs to have a lot of plusses over drum, but in an EV with regen braking you need far less mechanical braking.

[@flinch622]

@@Low760 "...isn't great" I can vouch for that having experienced seized wheel cylinders before on drums without rear access. Cant spin drum to get at adjuster so... pulling is a mess: bits all exit about the same time drum lets go and it all goes flying..

[@animefreak5757]

you don't want electric drum brakes on a car >

[@marklucas2591]

As an excellent automotive engineer, I am currently working on a system whereby using levers and pulleys you can drive your car while laying on the back seat.

[@gzcwnk]

Marketing = disks = racing = sells that simple. Good piece covering the aspects.

[@bigboy6704]

this is written like a video from a channel with 250k+ subscribers. well done all around

[@dogbots159]

Quick reminder that,as far as I can tell anyways, all EV have an established program to keep your disc brakes clean. Tesla highlights this more than others in their manuals. The pads will barely touch the disc randomly to keep themselves clean without slowing the car down. Just barely enough to knock off any rust or dirt. They do recommend occasional harder stopping from the highway just to make sure there’s no other issues for emergencies, but that’s not. Otherwise, these are all great points and well presented! 😊

[@eelcoberg392]

Tesla also says you have to clean and lubricate your brakes every year So there might be a rust problem that maintenance must keep in check . It's no wonder that Tesla's are doing bad in German Tüv statistics. People think it's a EV and doesn't need maintenance, until they show up at the mandatory checkup and have problems after 3years of not watching after their car's

[@RD-ce6bb]

Great content not found anywhere else thank you 👍

[@brianwaite6139]

One of the first things I did, when I built five EV prototypes back in 1972, was to convert from disc brakes to drums front & rear. Excellently explained by the way.

[@rayoflight62]

My Volkswagen Beetle had drum brakes well into the late '80s. I knew that I couldn't drive the car down a mountain. After braking for 1 Km, the brakes didn't work anymore and I had to plan for a brake break: basically, I got on a level street and wait for an hour. I was regularly replacing brake components. Merry Christmas!

[@johnarnold893]

Anybody with any sense would have gone down that hill in a lower gear. Please don't ever get into a highway truck and drive like that.

[@firstielasty1162]

Your Volkswagen beetle probably had the same drum brakes its whole life, with the exception of the occasional replacement of the shoes.

[@Chris_1024_]

Motor brake would have helped in sharing the potential energy dissipation down the hill. But anyway, that is not an isssue on BEV. A VW ID.3 has 75kW of regen capability, more than enough to take all the energy and charge the battery with it, not using the brakes.

[@johnbarry5115]

You make a very good point about underused discs going rusty, I've just bought a hybrid and it did occur to me that this could be a problem. I must admit that I was surprised at the amount of slowing down that you can get from regenerative braking, and I'm sure that with gentle driving, and looking ahead, the actual brakes wouldn't be used very much, if at all. It looks like when slowing down, especially in wet weather, we'll have to decide between recapturing that energy, or drying the brake discs.

[@alanb76]

At the end of each stop, below a certain speed, dynamic braking stops being effective, so the friction brakes are applied at that point. They don't wear much at these low speeds, but they do get exercised.

[@manekdubash5022]

Sadly, few drivers seem to look further ahead than the car in front.

[@balahmay]

Is it possible to have disk materials that are corrosion resistant?

[@neil1997]

​@@balahmaycarbon fibre? Think Porsche option stainless discs on the Taycan... But like exhausts, you'd think "technological advancement"would have us with ever-lasting components by now right...

[@TwinCam]

Carbon aren’t useable on the road, but carbon ceramic is, and won’t rust. However, it’s noisy and needs warming up somewhat, not to mention the expense!

[@SuperLittleTyke]

As an apprentice motor mechanic in 1961 I never saw disk brakes until much, much later. All the cars I worked on had drum brakes front and rear. I even relined worn brake shoes with brake linings off a roll. Those early brake linings contained asbestos. After riveting on the new lining with copper rivets you had to chamfer the leading edge of the lining so that the brakes didn't grab. Several years later we just got a replacement set of brake shoes from the local dealer or parts supplier, handing in the old brake shoes which were returned to the manufacturer to have the linings professionally replaced. In some cases drivers didn't have their vehicles maintained regularly so that the brake linings were worn down to the rivets and then the drum surface got damaged by scoring, so much so that drums sometimes needed to be sent away for machining to remove some steel in order to remove the score marks. This increased the internal diameter of the brake drum, therefore the brake shoes had further to go before contacting the drum, thus affecting braking performance. However, as I recall, slightly oversized brake shoes were available to compensate. There's a lot to be said about drum brakes, and I haven't even mentioned the wheel cylinders yet!

[@shakedown1979]

New time subscriber, stumbled upon your channel… Have to say narration of the highest order here, absolutely on point 👍

[@TheBlibo]

While brakes on cars are mostly hidden away the asthetic of the brake is is mostly lost if you look at motorcycles they have to look good as well as function and for me the best piece of engineering art has to go to the cma 8 leading shoe brake used back in the sixties on race bikes Great informative vid

[@fiftypence7623]

Well done mate! very informative........there will be a lot of 'dad car experts' down the pub and around the table this Christmas impressing everyone with their knowledge about the reasons why drum brakes etc. (including me!!]

[@TwinCam]

Thanks mate :)

[@tubaterry]

I had been noticing people mentioning drum brakes on a few models when I've been at charging stations lately, I was curious what that was about! I'm a newly-minted car nerd so this was a great lesson for me. Thanks!

[@kelownatechkid]

Very comprehensive coverage of an increasingly-important topic!!

[@benc8386]

Great video! A key difference you didn't mention is that when things get hot they expand. That causes "drum fade": the drum grows and the shoes don't reach it any more unless you push the pedal further or pump it. When a disk expands the pads grip it tighter. Great. But the situation is reversed when you park. As the hot drums cool down the handbrake comes on tighter, which is all to the good, but if you have a handbrake operating on disks, they shrink away from the pads and the car rolls way. Citroen Xantias were famous for this. Many ended their lives at the bottoms of hills. I think this is the main reason why many cars use the mini-drum. It's not that difficult to rig a mechanical linkage for a disk caliper (usually a jackscrew) and many Japanese cars (and I'm sure others) do use handbrakes on rear disks so it can be done. But personally I am still leaving them in gear as well :) Slots and holes in the disk I have heard are meant to be for deglazing rather than cooling (but this one of those things people argue about on the internet a lot).

[@normandiebryant6989]

The biggest problem of hot drums being parked is that, when they cool and grip the unmoving shoes tighter and tighter as you say, they then warp and become "ovalised". From then on, when you brake, the brake-pedal vibrates and they are more likely to lock up. This was a huge problem here in Australia but, sadly, because our cars were made by American manufacturers, we were just given drum brakes on the rear until well into the late '80s and even 2000s.

[@TwinCam]

Yes, that's all part of the inconsistency and fade they suffer!

[@elmarko9051]

@@normandiebryant6989 Here is USA I can personally attest to getting disc/drum well into the 2000's on GM minivans. Fortunately never had a problem with drum distortion. Literally just gave an 04 Pontiac Montana to my college-attending son here over the holidays, original rear shoes were fine, but one cylinder was leaky, and both were changed, less than $25 US total in parts. The only reason USA manufacturers changed was to have combo service disc/emergency drum so the emergency system was not reliant on a potentially failed rear drum. The 06 and up GM minvans have that style of system, rear 'top hat' style rotor with mini-drum inside.

[@martinclapton2724]

It was Jaguar who possibly pioneered disc brakes at Le Mans with the C Type , early 1950s , this gave gave a big advantage over their biggest Italian rivals, notably Ferrari. This not allowed less brake fade but also later braking . In domestic use , however, drums WILL stop you if everything maintained and adjusted correctly for a single or two heavy applications. If you have do too many heavy applications on a given journey , you’ve got something more wrong with your driving style , than the design of brakes on your car.

[@allangibson8494]

Drum brakes are more vulnerable to contamination by water and mud. Driving through water can result in nonfunctional brakes.

[@richardbell7678]

Stop and go traffic is also terrible for causing brake fade. While driving through a snowstorm, in a '76 T-bird, it was either ride the brake pedal or hit the guy in front of me. The rear drums overheated, so there would be no rear braking, even after the fronts had completely locked up. Being RWD, the T-bird would go out of control. I spent the next two hours abusing my transmission, bumping it to neutral if I was gaining on the car in front of me and bumping it to drive when it began to pull away (a police officer told me that stopping in the emergency lane to let my drums cool might impede the progress of an emergency vehicle).

[@TwinCam]

I'm led to believe that 911s didn't have a brilliant relationship with discs in the early days owing to the weight distribution?

[@DeanJuvenal]

Many thanks from a motor cyclist and car driver since the late 1950s. Clear concise and very comprehensible. Congratulations.

[@andrewoffer7369]

the early vw polos had drums at the rear and discs at the front with no brake servo. Stopping was not one of its strengths

[@TwinCam]

Yeah, those '70s Volkswagens aren't known for their ability to stop!

[@chrisford4009]

I've learnt something today didn't know ev use drums but it do make sense now you mentioned regen braking and not using actual brakes cheers great video

[@rogerking7258]

Very interesting, and very well presented. The only argument I have with this is that my totally drum braked 1958 Frogeye has far and away the best brake pedal feel of any car I've ever driven, albeit you have to shove hard with no servo. Does this mean that we can expect to see the return of the old "try your brakes" road signs after fords? One problem with drums is that they fill up with water if driven through a Ford and then don't work until they've emptied out.

[@TwinCam]

I would assume, though it is an assumption, that this is more to do with the lack of a brake servo? The best brake pedal feel I've ever experienced was in both a Wolseley 1100 and a Fiat X1/9, both of which had discs, but no servo.

[@swecreations]

The brake discs and pads on EVs have an estimated lifespan of over 20 years, which is pretty crazy, know a guy with 700k kilometers on the original pads.

[@jimmyandersson4599]

The best advantage is that they will last forever in a EV. How I know that, I used to own older heavy concrete-trucks and these had drumbreakes and i never changed the breake-shoes. I drived one truck for 400.000km and did never change the breake-shoes, because they was okey in every years annual check-up.😊👍

Been playing with cars for over 50 years and found this very interesting and making a lot of sense to me. Keep it up kid love your videos 😁👍

[@TwinCam]

Thanks Mark :)

[@richardw1970]

Excellent job Ed, I think you missed a handbrake option though, a second set of pads mechanically operated acting on the disks as per late 2cvs and presumably other front handbrake disk fitted Citroens. As an EV driver I can confirm the friction brakes do very little of the normal braking and are crusty looking most of the time.

[@21stcenturyozman20]

Similar to the Citroëns you mention, my 1964 W112 Mercedes-Benz 300 SE coupé had separate parking-brake pads/actuators on the rear discs. Unfortunately, they tended to be ineffective, especially if one, typically, applied the handbrake when the rear discs were hot; when they cooled and contracted, those little parking-brake pads lost their grip on the discs and the car could roll. Thank the gods for the parking pawl in the auto box. A different approach - finned aluminium drums - were used on my 1965 W111 220 S Benz. The park brake never failed, and the drums didn't expand much because they were finned, so far less fade under extreme use.

[@TwinCam]

Thanks Richard, but as I said in that section of the video, we're ignoring the exceptions and keeping things simple. If we went over every variety and eventuality, we'd have been here all day!

[@kimpatz2189]

In the issue of cooling drum brakes. The Asian truckers prefer to cool the drums by blasting it with water during downhill. It even has an option to cool hub reductions and differentials during uphill. There are many kits for large trucks that can be installed fairly quickly. It is not a manufacturers standard so you have to install it yourself. Hired drivers are more prone to brake overheat than owner operators especially those who invest in water cooled drums system.

[@mickvonbornemann3824]

A flat contact patch is so much more efficient. Drums have a curved contact patch, which means in reality most of the contact patch doesn’t actually contact. It’s rare for even perfectly adjusted drum brakes for the full shoe to contact the drum. BTW drum brakes are no cheaper to make than equilivent disk brakes.

[@tigerseye73]

Drum brakes, per wheel, are also lighter in weight than a disc setup. Drag racers have used that little secret to shave a few tenths of a second in the quarter mile. The drum brakes are well within their capabilities to slow the race car after a short run without boiling the brake fluid. And they don't produce unnecessary drag at the wheels. It often means the difference between winning and losing.

[@marcbrasse747]

Very insightful. The main question is actually if mechanical brakes can be deleted. Will an electric car always need a mechanical backup brake system or can electric / electronic brakes become so dependable that the chances of complete failures are as low as on existing systems?

[@lwilton]

As a practical matter, no. The problem is simple. Dynamic braking becomes less effective as the speed decreases. At zero speed there is zero braking effect. So if you park an EV with no brakes on a hill, the car _will_ roll down the hill, because there is nothing to stop it. The motors may be able to limit the speed of the downhill roll (because the dynamic braking becomes more efficient as the speed rises), but they can't hold it in place, unless the motors are continuously generating forward torque to counteract the pull of gravity. Obviously this will drain the batteries on the vehicle if it isn't plugged in, and then it will roll away. Even if it is plugged in, you are continuously using electricity to counter the pull of gravity. A mechanical brake will prevent rolling at low speeds with no power consumed and no resources used.

[@marcbrasse747]

@@lwilton Good remark. Hadn’t thought about that. That problem can however be solved with a non friction system. A relatively simple and light mechanical lock could solve that problem. A low powered unlocking solenoid could even be used as an extra safety feature to avoid engagement during use.

[@RickJohnson]

Regen only works if the battery is not full or operating within normal temperatures. If the battery is too cold, too hot, or near max charge, most BMS will avoid dumping more energy into the battery, thus friction brakes are still required to stop. Plus, in an emergency, friction brakes still react quicker. Speaking from the perspective of prior ownership of 3 Toyota hybrids and a now a Tesla Model 3 BEV.

[@marcbrasse747]

@@RickJohnson Thanks. Very informative. There goes my patent! 😁

[@marcbrasse747]

@@RickJohnson PS: One could however imagine a solution in which the system even takes care of that. When range future range is less of an issue a small part of the battery capacity could be kept available under all circumstances. Maybe capacitors could also play a part.

[@Pepe_Le_Peugeot]

Well done on this video. Well researched and presented; your style is engaging and easy to understand 👍

[@xaenon9849]

I'm surprised that the video didn't mention the fact that drum brakes are self-energizing. The way the shoes are mounted inside the drum, and the way they pivot, means there is a 'leading' shoe and a 'trailing' shoe. The leading shoe pivots INTO the direction of the drum's rotation, causing it to dig in a little harder than the trailing shoe, and the slight movement this generates actually helps apply more braking force. This is actually the 'grabbing' he spoke of. It's not an issue in normal braking - it only really becomes a problem in hard braking, and it is why rear ABS became a thing. The 'self-energizing' aspect of drum brakes might only provide another 10 percent braking force, but it makes power assists unnecessary (particularly in small vehicles), and it also means less power is necessary to operate them - both important considerations in an EV. I am glad he mentioned the inherent parasitic drag of discs, though. The heat buildup issues of drums can be mitigated somewhat by 'partial' venting - basically, a series of small holes drilled into the outward face of the drum itself. But as he stated, this is less of an issue today than it was decades ago.

[@andrewthompsonuk1]

The biggest downside of drums I have found is adjustment. Automatic adjusters fail before anything else goes wrong. On cars like the Metro that have a manual adjustment its maybe better as you give them a tweek at every oil change. (If someone has not rounded off or snapped off the adjusters) The VW electric cars are rear wheel drive and very heavy so when the rear brakes are needed (normal rear braking will be done by regen) they are going to have to work hard like the rear brakes on a loaded van so it was no surprise to see drums on them.

[@peterjackson6228]

Excellent video! Some really good points there. Also interesting to note that EVs are fitted with plastic wheel trims, even though they have alloy wheels, the reason being is to control air turbulence (apparently). I'm sure next they'll be fitting manual window winders too 😂

[@AndrewTSq]

Its been used for a long time by many cars. Remember BMW M5 from the late 80ies? it had those wheeltrims that sucked in air to cool the brakes for example. Best is to actually hide the wheels completely, like the Volkswagen XL1 has done at the rear, or like older Citroen CX used.

[@oldschoolman1444]

My daily has hand crank windows. =)

[@TwinCam]

It's amazing to see manufacturers suddenly start caring about this kind of efficiency in a way they never did with ICE vehicles. Imagine how high they could make the MPG if they actually tried!

[@AndrewTSq]

@@TwinCam They did, that is why the Volkswagen only uses 0.1liter of fuel per 10km. :) I also remember in the late 80ies that the CV value was also brought up a lot in car reviews here. I think Opel had some cars that was aerodynamic around 0.25 in the mid 80ies. But fuel was realitve cheap back then, so you did not really care at the time.

[@haukionkannel]

Modern EV with heat pump takes heat ebergy back from many sourses… hoe about the breaks?

[@1darryloflife]

Now have a look at "Wet Discs" first brought out by a tractor company. Housing the disc and caliper in a drum cutting a 25mm wide groove in the disc pad and then placing the disc and caliper in a sealed drum filled with automatic transmission fluid, whalla you have the ultimate braking device giving full control by the driver over the vehicle's ability to stop. Of course the wet disc brake is only good on the front axle.

[@ricolasroc5890]

Great video. Fascinating, and thought provoking. Lots there to ponder on - thank you so much!

[@TwinCam]

Thanks mate :)

[@danceswithmules]

It's worth mentioning that drum brakes get a mechanical advantage, too, with all the contact area out on the outer diameter while disk brakes have their contact area within a range of diameters. Therefore, all the braking force is at the maximum moment arm.

[@barongerhardt]

Which break has more breaking power has been a pointless argument from the beginning. If the breaking system is good enough to lockup the wheels, having more breaking power adds nothing. The electronic control of drum breaks to make up for the worse peddle feedback/control is an interesting issue.

[@animefreak5757]

thank you.. I couldn't count how many times i've had to point this out to people.

[@TwinCam]

I mention exactly why I have to say that line - because the memory of drums has to be ameliorated. Cars in the ‘50s had crap brakes because they just weren’t up to standard, not because they were drums specifically. Yet half of the comments section here is convinced that because a Morris Oxford took 30 miles to stop, it must mean that every drum-equipped car must too 💀🤣

[@DrewNorthup]

(1) I had a 1995 Geo Metro for a few years. It was a joy to drive, got awesome gas mileage, and had an amazing amount of cargo space (so long as that cargo wasn't too heavy). It also was supremely balanced, spinning exactly around the stick-shifter (don't think too hard about how I would know that). (2) My current vehicle, a PHEV, seems to be programmed to take into account the maintenance needs of the disk brakes-virtually always kicking them in before the car has stopped rolling. (3) Properly built & maintained disk brakes DO NOT drag when released. The brake shoe / pad combination is actually a spring which is flexed when squeezed and retracts the pad from the disk upon release. If they did not do so they would wear DRAMATICALLY faster. This is also why one does not only measure pad wear at the leading & trailing edges as it is the wear in the middle which determines when the brake will fail.

[@bertoltb1358]

Very informative, great work. Merry Christmas to you, all the best for 2024.

[@TwinCam]

Thanks mate :)

[@richardhunt1384]

6:24 not ever car with rear discs use a drum in the middle for the hand/ parking brake. Manufacturers will put the hand/ parking brake into caliper which use a cable to activate the brake or nowadays manufacturers are using electric motors for the parking brake. This can cause an issue when changing pads as the system has to be put into a Service Mode in order to push the pistons back. 12:25 I'd also say that a Golf is FWD whereas an ID3 is RWD. Braking components are coming down in price (although prices have gone up from suppliers, what was a relatively cheap disc and pad combination for say an Astra a few years ago has shot up but obviously that a Global issue) due to fact that suppliers don't want the old parts back. We use Napa parts at work and it astonishes me the amount of parts we simply throw in the scrap. I threw two drivers shafts for a 1 series yesterday as well three brake Calipers and brake discs. Year ago suppliers would have surcharged for the calipers and shafts and VW used to surcharge for water pumps..... now we throw them out.

[@perdanielsorensen7775]

A cheap third party VAGCOM reader can put the brakes into service mode. I've got one from Biltema. It cost me NOK 999 (GBP 77.04). Older calipers with parking brakes are annoying because you have to turn the piston while pushing it in when replacing the brake pads, at least on the ones I've come across.

[@TwinCam]

As I said in that section of the video, we're ignoring the exceptions and keeping things simple. A number of cars also use a front axle handbrake that acts directly on the driveshafts.

[@martymiller4300]

Drum brakes are superior to discs in only one respect, they make better static (parking) brakes. They are inversely affected by heat as the diameter of the drum expands, taking the steel surface away from the friction. The violent automated pumping that is ABS is compromised by the excessive movement between the friction and the steel and the wheel cylinder is more likely to be damaged by the movement than a caliper. Servicing drum brakes is a technichian’s nightmare, the final step of adjustment is a game played inside a sealed box. One of the reasons discs took on so well in competition is service time on pit row. But the biggest hole in this picture is the excessive weight involved with E V batteries. Stopping an extra thousand pounds cannot be done better with an inferior system. Excellent video, good theory but I’m not buying it. Drum brakes are returning because they’re cheaper to manufacture and set up on the assembly line when everything is new and perfect.

[@TwinCam]

As I say in the video, the heat is no longer an issue, and with electronically-distributed braking, drums are capable of larger stopping forces.

[@martymiller4300]

@@TwinCam I’m sorry but what we are talking about is a device that turns kinetic energy into heat via friction. While regenerative braking takes on a portion of the task, heat has to remain an issue at the wheel brake. And if the inferior drum system works better with electronic controls then it makes sense that a superior disc would respond even better to electronic controls. When drum brakes return to Military and commercial aviation or Formula One racing you’ll have me convinced.

[@TwinCam]

@@martymiller4300 The brakes aren't being used though. If configured correctly, regenerative braking will stop the car. To mention aviation and motorsport is to simply ignore the central point of the video.

[@martymiller4300]

@@TwinCam you’re right I’m being pedantic

[@saginaw60]

We see a lot of stuff about brakes on the net. Wish people would talk about brake fluid. As an old mechanic, experience has taught me, that if you want to save money and have good brakes, CHANGE THE FLUID. Extremes of temperature (thermal excursion) cause it to thicken. No one believes me, this issue has caused many a bar fight.

[@TwinCam]

Anyone who doesn’t change their brake fluid every two years needs their head checking.

[@roberttaylor6295]

Ed, you demystified a complex matter of car brakes which as a non-electric car owner I have not fully appreciated the difference between drum V discs via your excellent research, super scripting and energy and bubbling enthusiasm . So ignore the petty nonsense of those nit pickers who seem more intent on looking at your eye movements than the excellence of you video presentations based on your engaging, didactic motoring professionalism! Rob

[@TwinCam]

Thanks as always Rob :)

[@markedwards4879]

Drums require more maintenance and perform abysmally if that maintenance isn’t done. They are inconsistent in use. I would not buy a car in 2023 that uses them, EV or not. Your reference to the cost to replace a calliper is weird to me. In over 40 years of driving I have never needed to replace one on any of my vehicles. Maybe this is a warm weather thing - here in Australia we don’t have salty winter roads - but even when living right next to the ocean where *everything* corrodes I’ve never had a problem. The last vehicle that I owned with drums on it was my 1981 Yamaha XJ750, or a 1988 Camry that I bought for my partner to drive. Sure, the parking brake is simpler with drums but that doesn’t outweigh the disadvantages. As for disk rotors rusting, a simple software solution is to have the car dab he brakes every so often when braking. Tesla does this, and uses disks. VW just cheaped out with their EV as they were already losing money on them and needed to keep costs down.

[@TwinCam]

It might be a climate issue, but I'd suggest you've just been exceptionally lucky. I've had three cars and have been driving my own cars for four years. I've needed two new calipers. On the other hand, one drum adjuster seized, but that's a much cheaper and easier job to replace!

[@markedwards4879]

@@TwinCam What was the problem with the calipers? There isn’t much more in them than a drum brake. A piston or two, and a couple of pins fins for sliders and the brake pad itself. Aside from upgrades, I’ve never even had a mate who replaced a caliper.

[@Chris_1024_]

VW says the drumbrakes last for a lifetime, no maintainance at all. And lower maintainance and higher lifetime has always been known advantages of drums. That is why hgh milage Trucks use them.

[@markedwards4879]

@@Chris_1024_ You’ve obviously never owned a car with drum brakes mate. Trucks use them because they are cheap. Air disk brakes are very expensive.

[@Chris_1024_]

@@markedwards4879 So as Semis and trucks main goal is to be competative and cheap to maintain, as that affects revenue, couzld yopu please tell me why ALL truck companoies are unbelievabley superstupid to buy trucks thatr havt the mosr ext´pensive break option? Why are tSemi manufacturers not as smart as you and only builöd trucks with disk brakes that are far cheaper to maintain in your opinion nand therefore superiour as an asset to have becasue of the low operationg cost? Why dom you think all those engineers, truck comopanies and users are so0 much moste stuzpid than yopu and don't get it?

[@briant7265]

The biggest enemy of drum brakes is water. I drove my '54 Ford's through a healthy puddle, long ago. A tragic light turned yellow on short notice, and I hit the brakes hard. The right side of the truck stopped, and the left side didn't. I also had a'70 Mercedes. It had 4-wheel disc brakes. The parking brakes used small drum brakes just inboard of the rear discs.

[@peterriggall8409]

Thanks for the entertainment Ed. especially the BMC/Leyland stuff and especially the 3 litre video.

[@TwinCam]

Thank you Peter, you’re far too generous!

[@mcmaddie]

Drum brake inside the diskbrake must be cheaper than the alternative that I had already in -85 Audi 200. It had discbrakes in the back and parking brake used them as well. Piston was pushed with a rod that was actuated by the parking brake handle. No need any extra drum brake just for parking brake.

[@Low760]

Volkswagen use them still.

[@michaelovitch]

You didn't mention weight distribution on axles,wich is mostly the reason EV have drums on the rear. EV are way heavier ,they have more weight on the rear,less mass transfer during braking,so less risks of reduced tire grip. Brake force distribution is not the same at all on EV A diesel fiat doblo of 2018 will have drums at the rear,while 1.7 ton : it's mainly a utility vehicle ,often loaded at the rear with stiff suspensions ,so mass tranfer is low.

[@oldgysgt]

One correction; drum breaks don't fade when hot because the shoe and fluid are getting hot. The fade is caused because the drum is heating, and being made of iron or aluminum, and metal expands with heat, the drum expands in diameter, and away from the internal break shoe. The major advantage of disk breaks an your average passenger car is that when heated from constant use, disk breaks don't fade to any extent.

[@billmaghan]

Thank you for captioning. Interesting and informative video.

[@thatcheapguy525]

really good explanation Ed. God help us though if we're going back to drums. theory is one thing, reality another. drum systems fade, seize, the wheel cylinders leak fluid (as can be seen all over the shoes of your Metro), adjusters snap, they're a much longer job to replace, the concentration of heat blows wheel bearing seals, drums warp and the shoes have a tendency to drag against the drum unless everything is maintained perfectly. on the other hand, most disc systems provide the opposite and should self-clean in operation. handbrakes have however been another story as you point out. all that said, times move on so maybe the EV generation of drum brakes have some clever technologies in them? a humourous but true point comes to mind. how do you adjust the drum brakes on an original FIAT 500/126? do 20mph in reverse then slam on the brakes - job done!

[@TwinCam]

Thanks mate :) They do have service issues, but so do calipers leaking fluid through the seals and having their pistons seize!

[@thatcheapguy525]

@@TwinCam thanks for the reminder Ed. its been years since I've done piston seals (goes back to MK3/4/5 Cortinas!). some designs suffer from the sliding member of the caliper seizing also. much of the issues come from poor quality materials in manufacturing and improper/rushed replacement of the brake service or consistent driver abuse i.e. driving a standard family car like a race car without upgrading the brakes lol. keep up the good work mate. love the channel. I'm fascinated to see where you'll take it a year from now

[@Chris_1024_]

So tell me, why do the vehicles that drive the highest milage, trucks, semis, use drumbreaks if they are more expencive to maintain? On BEV they aren't used anyway but for emergency braking, so it's a no-brainer to go for drums. VW says the drums last a lifetime and are maintainance--free.

[@thatcheapguy525]

@@Chris_1024_ I'm no expert on heavy haulage drums but I do know their conventional systems work differently with a pneumatic system that defaults to on (cars hydraulic systems default to off) so for the vehicle to move first thing in the morning it must first release its brakes, maybe this is part of the answer? these vehicles are also restricted to 56mph in European countries so there is less need for higher quality machining. drums are cheap and heavy haulage is probably the most price sensitive type of vehicle you can buy. and don't forget convention in a sector which evolves very slowly. listening to a couple of mates who drive 40 tonners, they regularly complain about trailers they hook-up having poor/useless/unbalanced brakes. regarding your statement regarding VW drums, as I said in my original post "maybe the EV generation of drum brakes have some clever technologies in them?"