How a Dual Clutch Transmission Works

Here is a look at what’s inside a dual clutch automatic transmission and how it works!
A dual clutch transmission is internally very similar to a manual transmission - with the exception that the computer (mechatronic unit) is responsible for physically shifting the gears. Instead of a single dry clutch like in a manual transmission, a DCT uses two wet clutches, one larger than the other one to drive two input shafts to the transmission. The two input shafts will power either the even gears or odd gears.
Other accessories to the transmission include a transmission cooler, oil filter and oil pump that serves to cool and lubricate gears and bearings. The transmission computer is located inside the transmission mechatronic unit, which control solenoids to redirect fluid flow through a valve body. The valve body will in turn feed transmission fluid through the housing and into the pistons which will control the position of the selector forks and thus select the gear.
One advantage of a DCT is that it can shift gears much faster by preselecting the next gear that the computer thinks it will shift to. It does this by engaging the fork of the opposing gear that is currently being used. The downside is that it can often get confused if the driver has erratic inputs and therefore cause hesitation or jerky output.
Finally, while the wet clutch and gear synchronizers are often wear points on these transmissions, the mechatronic unit is often the fault for many failures.
The transmission in this video is a DSG (direct shift gearbox) D250 unit from a 2006 Volkswagen Jetta TDI.
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[@jessicaandtrains7768]

I often watch videos at 1.75x speed but yours I was able to watch at 1x. Great editing and no time wasting 👍

[@speedkar99]

Glad you like the speed, I thought it was too slow

[@liver.flush.maestro]

@@speedkar99 The speed is just right for me, I still needed to pause and go backwards a couple of times.

[@prveteran]

I still continue to be highly impressed with your knowledge on cars. You're like a neurosurgeon working on cars. UNBELIEVABLE. Like a walking encyclopedia. Good for you!

[@dehypnotizer]

Great vid, as usual. Those clutch pads are in mint condition given the fact that the vehicle drove over 300 kkm. Looks to me like a great piece of engineering.

[@speedkar99]

Sure is quite the engineering. However I have no history on the car if these clutches were changed before....

[@dehypnotizer]

@@speedkar99 You're right, I didn't think about it - it could've been replaced at some point.

[@easley421]

@@dehypnotizer I've got a manual v dub. This DSG tranny cost over $300 to service. The manual was $50. Though some things are engineered well, others like the plastic water pump.....not so much. I've got a Japanese car for EVERYTIME something breaks on my v dub.

[@dehypnotizer]

@@easley421 What failed in your transmission? I have a DCT and it seems to be quite robust (2nd car, no service, except oil changes, required).

[@easley421]

@@dehypnotizer Nothing failed in my tranny. It's a six speed manual, BULLETPROOF. What I was saying was the service for the transmissions were vastly different. The DSG first service 300$, my manual $50. I have a 2013 Volkswagen CC. So far I've had to change the water pump, the fuel control module on top of the fuel pump, rewire the wires connected to the trunk lid because they crease and cause the car to become possessed when the wires touch. I'm not even joking, my girl put it in reverse one morning and the trunk popped. I go up in there and pull the wiring harness out and they're all frayed to shit. There's been a few other incidents with this car, all the while my 2006 G35 remains running, without an issue. My buddy is a mechanic and sent me a pic of a new Dodge Ram tranny filter change. The entire pan of the tranny.......PLASTIC! With the filter BUILT IN. This shits not gonna get better. Hold on to anything between 2001-2009. The best years for cars and bike IMO

[@borntojoke97]

As a junior (thermal/aero) enginner in the automotive, I consider these videos pure GOLD! You would not believe how much stuff we learn in school, and even on the job, but especially now with electric vehicles everyone specialises on just a tiny parts/systems of the car. Seeing this stuff is so interesting, and it allows through your eyes and experience to have the general view of all the systems! Plus now, a lot of these mechanical parts will be gone with EV, so I try to learn what I can before they disappear completely! Thank you!

[@speedkar99]

Glad you learned alot. I too didn't learn any of this in engineering school

[@michaelbezoski3096]

Literally blown away. The machining to make it all work is only matched by your explanation. Thanks for all the effort to teach me why bicycles still have a place in this world (maybe horses too). Your #1. Still do not understand how you can sit cross legged based on the Mrs. cooking. You two are real stars of youtube!

[@ufartface]

makes you appreciate the simplicity of a manual transmission

[@arctus35]

Wanted a DCT video for a while now. Great video as always.

[@milesredgate4596]

Transmission's always make my brain hurt, but I think this is the first time I feel like I've understood something about their mechanicals.

[@thatguy1919]

Wow I can’t lie I was expecting all the parts to be worn and in poor condition, glad to see VW manufactured a (mechanically) reliable unit.

[@dragonofyorha]

I personally find that people give VW a bad rep. All you need for your VW product to be reliable is treat it kindly. But that’s just my opinion.

[@thatguy1919]

@@dragonofyorha well to be fair VW cars have been known to have electronic issues and become expensive to maintain once they reach a certain point down the road.

[@joskd8491]

Nope, it's quality is not very good

[@PDD87]

The newer gen. of DSG are More reliable than the first one. The first gen. was crap

[@joskd8491]

@@PDD87 less worse, you mean....

[@mscir]

GREAT video, I had no idea how these worked. The condition of the clutch disks is amazing. Great design. Thank you.

[@speedkar99]

You are welcome! I didn't know much myself until tearing this down and researching

[@nickchannel5364]

He has a dry sense of humor. Love it.

[@speedkar99]

Glad you get it 😏

[@Erik_Swiger]

That bit you said about the transmission becoming "confused." This is exactly the problem I have with modern car technology. The transmission itself is fascinating, and in theory, a great idea. But making it so complex that it cannot function, is a bad idea. I can't imagine a Turbo-Hydramatic becoming "confused." Great video, and as always, I love your choice of rags to clean up with.

[@speedkar99]

Yeah unfortunately the nature of DCT's being able to shift quickly relies on alot of computer input. As algorithms get better that should be ironed out.

[@AKAtheA]

a late turbo-hydramatic has a whooping count of...4...gears that are wide and torque converter lockup came around in the 90s. If you're fine with the garbage gas mileage, then sure, keep the "unconfuseable" dinosaur which shifts at glacial speeds. If you want a smaller, lighter and substantially more efficient auto gearbox, you need a computer. Or a manual transmission...

[@arielbatista7ify]

As a software engineer I have no idea what he is talking about, but I think that transmissions are made with magic

[@speedkar99]

As a mechanical engineer I have no idea how computers work. I think they're made with magic

[@Tu_Estrella_official]

Your knowledge on mechanical theory is definitely A+ thank you for this video you kept me tuned in from start to finish 🙏

[@keremardicli4013]

These are very valuable spare parts. Hope they get to work again some day.

[@kylevarble2325]

Absolutely love your videos very educational and hilarious I appreciate all you do. Watching your videos is so easy because your not afraid to show your process of figuring it out when others cut that out and try to look like they know it all and don't make mistakes. Keep it up I look forward to all your videos

[@speedkar99]

I'm glad you like them, feedback encourages me alot. For me, the process is if it doesn't come out, then the angle grinder will take it out haha

[@doglegjake6788]

I'm very thankful for what I've learned from this man.

[@petergreen5337]

Thank you very much publisher for this beautiful lesson and demonstration .

[@HugeRademaker]

I so love it if someone exactly knows how things work!

[@markdavis8888]

Your appropriately used fast speed is wonderful. I wish everyone used it in their videos.

[@speedkar99]

I'm glad you like the pace. Sometimes I think I'm too slow

[@motoshoota]

Amazing video as usual, thank you for putting out straight knowledge, you’ve taught me a lot so far

[@martynjames5963]

Great video. Understood everything ...except ... how could anyone invent this!!! Pure genius. Nobel prize material!

[@speedkar99]

It sure is genius. But not very popular as the Mechatronics unit typically goes on these

[@oscarlmolina]

Great video! Love the way you explain how things work

[@speedkar99]

Thanks!

[@MatthewWaddell-zg5up]

Incredible video. The editing was great, explainations were simple, and your snap ring tool made me giddy. I'll always sub to this kind of AAA content.

[@yehudaegert2276]

Great explanation without the "mandatory" 25 minutes of "filler content" to make the video longer

[@test40323]

Oh, excellent breakdown. I like the way you explained the gear selections but unfortunately you lost me between gears and splines. Good thing no exams at the end. :-)

[@SvcGlobal]

Excellent video as usual, please keep coming, thank you!

[@doctorrobert60]

While looking very complex amazing it works as seamless as it does. Been driving manual transmission cars for long time but recently purchased a 2022 VW Arteon that has the wet clutch 7 speed DSG. Hope it is as dependable as standard manual transmission. Thanks for posting the interesting and elucidating video!

[@speedkar99]

I'm not sure about VW's recent DSG but the older ones had issues with the Mechatronic unit

[@doctorrobert60]

@@speedkar99 Thank you for your input!

[@johnw3379]

Fantastic video! You are a Very smart man! Thank you for spreading your knowledge with everyone on here! I really enjoy your humor!

[@speedkar99]

I'm glad you like it 🙂

[@kristianhermann5971]

Transmissions are so cool - thanks SpeedKar

[@dgurevich1]

The complexity of this gearbox is mindboggling. No wonder nobody wants to touch these. I had the un-pleasure of driving a car with single clutch robotic, and if this one shifts as slow as the one I had (the actual movement of the forks, not the clutch engagement), no wonder the internals are that well preserved.

[@speedkar99]

DSG are one of the faster shifting transmissions. A single clutch would take a much longer time to shift

[@GunnyPhillips]

Amazing work my friend. Thanks so much for this.

[@zaraak323i]

I wish I had your snap ring removal tool when I was replacing my steering lock last week!

[@TimmieTennis]

Love the toothbrush… this some of the best content on KZbin!

[@speedkar99]

Glad you appreciate it

[@jonnathonclayton5005]

That preselecting explanation is the best i have heard, wonder why triple clutch transmissions are not a thing, it would have major benefits to be able to preselect a gear above and a gear below so it's always ready with zero hesitation i would think...

[@seancarr7018]

Special snap ring tool definitely gets a thumbs up

[@speedkar99]

Well thanks!

[@seancarr7018]

@@speedkar99 yes sir. I very much enjoy watching you tear things down and explain them. Your videos are great and always entertaining and educational

[@electronicengineer]

@@speedkar99 A well deserved "Thumbs Up", I must interject. I absolutely LOVE your channel. I wish YT would have shown it to me years sooner. Your dry sense of humor, coupled with your incredible knowledge, is a winning combination, at least in my opinion! Thank You for all the effort that you clearly put into making these videos, which definitely make me and I am sure a few others, just a bit smarter! You ROCK!

[@devinmccormick1165]

great video, super informative

[@thedarkknight4243]

Great video, thanks for the information and knowledge.

[@tomlewis3658]

Thanks for another informative video. Your snap ring removal tool really gets the job done. Maybe you can sell it under the Snap-Off brand.

[@2icelollys1goat]

Fantastic video and explanation. One of the best I've seen👋👋👋👋👋

[@hrvojeglavas]

Thanks for the useful material!

[@Ts68mo]

THANKS FOR THE GREAT EXPLANATION

[@speedkar99]

Welcome

[@lewisavinash1]

i loved the snap ring removal tool, yesterday i used that tool to remove siged car wiper bolts, i keep two of them handy 4 inch and 5 inch chorded and chordless

[@jessicaandtrains7768]

At some point I need to get better clutch plates etc for my dual clutch BMW. Good to see even regular clutches in various cars are strong.

[@speedkar99]

What happened, is your dct clutches going bad?

[@rawbennett]

Your videos are put a smile on my face every time!!! Keep it up ;)

[@speedkar99]

I'm glad you appreciate it

[@stephenhorton1933]

Great description

[@speedkar99]

Thanks

[@Theo0733]

👍👍👍thanks millions bro. you do better job than my teacher does!!

[@jamespeterson4125]

Thanks for not wasting my time. Very interesting.Looks like some motorcycle technology there.

[@ginog5037]

Excellent teardown, definitely a great transmission, too bad their TSI suck. FYI drain and fill is pretty easy, once drained you can fill through the filter. It's a little slow but works fine.

[@speedkar99]

Good to know. That probably would make a mess though

[@ginog5037]

@@speedkar99 Not at all use a long neck plastic funnel, melt the end to the filter port hole easy peasy.

[@aMadHouseProduction]

Very helpful...thank you

[@MrSamPhoenix]

Pretty cool video man, I’d love for you to do a transmission review of Honda’s 10-speed transmission & the ZF 8HP series as well.

[@victorwilks88]

Your videos go so quick

[@johnmadsen37]

Simply amazing what men have invented.

[@oscarchakanetsa8425]

Great video as usual

[@moorec1053]

Damn......... this guy is VERY Good..!!! Thank You My Friend 🙂

[@MSI2k]

Awesome video!

[@dsbohra]

Brilliant.

[@tjthenovicerider1138]

My question is how they change gears smoothly when they are friction clutches engaging so fast. On manual transmission, if you release the clutch quickly you will experience a slight jerk even if in correct rpm.

[@doglegjake6788]

I would have to go to Yale University for 10 years to learn what I've learned from this 1 video.

[@Sera5e]

"It's not winter yet" 🤣 Subscribed!

[@Sera5e]

@speedkar99 legit?

[@stevenhohn8644]

@@Sera5e hell no

[@Sera5e]

@@stevenhohn8644 Typical, I never win anything 🤣

[@marco1173]

It's hard to describe the feel of a DSG transmission to someone who's used to regular automatics, so great job doing that in your vid! My MK6 GTI has the DSG and I love how lightning quick the shifts are. My only dislike is getting going from a full stop, as it can be a bit rough. I've learned to just give it more gas than you'd think as opposed to easing on the gas pedal to try to gently roll off the line.

[@speedkar99]

I agree, the first time I drove this car (MK5 Jetta) I was surprised at how fast it shifted. It also short shifted but then again it was a diesel

[@supersabrosinho]

Still not as direct as a conventional MT, but it's a nice compromise between AT and MT

[@cernejr]

Nice video. Lot of engineering went into designing and manufacturing of this transmission, I am impressed. I drove a Porsche Boxster with a DCT, it was a very good unit, crisp/fast/precise. But I personally prefer manual transmissions.

[@speedkar99]

Yes the shifts are very fast, and that's the main advantage here over the manual.

[@salami99]

I always noticed on every transmission that reverse tends to be ratioed between First and Second gears.

[@CDeuce152]

I have a 2021 Kia Sorento with the 8 speed wet DCT. Aside from the clutch setup and number of gears it's basically the same basic functions.

[@speedkar99]

Yes, it's mechanically a manual transmission

[@Fred-F4]

Awesome video!! So informative! No torque convertor is really not a good idea in an automatic, will not get a DCT car ever

[@speedkar99]

Thanks. The concept is good, but the driving feel is a bit weird at slow speed and that's when the clutches wear the most

[@operator8014]

Ohhh. I always thought the final drive gears was included with the clutched mass. I guess it makes sense that those would be unclutched though, lowering the inertia for synchronizing.

[@speedkar99]

Final drive typically means the differential right at the wheels

[@operator8014]

@@speedkar99 Yeah. I just thought the twin clutch idea was a clutch on the input between engine and input shaft, and another clutch between the final drive and the output shafts. Don't know what system I was looking at that worked this way, but I just assumed they all worked that way.

[@markw3922]

The larger clutch pack is for 1st gear plus etc ?

[@ItsMe-ld3fs]

Please make more videos on electronics

[@eiffon]

god i love these videos

[@shiroyasha4995]

this video is sponsored by oral B. your trusty teaching tool in engine parts

[@leetos.4915]

If I don’t shift from drive to sport mode at all, would it prolonged the clutch disc life more than 100K or maybe 200K? I have a dct transmission in my 2017 ioniq

[@elijahallen]

Great video, I am trying to find a problem my dq500 is having with going into drive. When I start the car and put it in drive it won't engage until the car is completely warmed up. If I give it a little gas it will engage but it slams in so hard the tires chirp. Once the car is warm it engages fine and drives and shifts with no issues. I replaced the hydro tubes hoping that would fix it but it didn't. Any idea what would be causing this? Thanks

[@speedkar99]

Sounds like you aren't getting enough fluid pressure

[@elijahallen]

@@speedkar99 What controls the fluid pressure? I am stumped on what to replace.

[@emanuel4491]

Great video. I prefer VW’s approach to DCT’s over Honda/Nissan going to CVT’s, both in terms of performance durability. Which do you prefer having taken both apart?

[@speedkar99]

DCT It's basically a manual transmission and you can replace just the Mechatronic unit as opposed to the whole thing when it fails.

[@It5M3Again]

I thought honda and toyota CVTs go for over 200000 miles though.

[@harfenspieler]

VW DSGs have a repuration of lasting either 300000 kilometres, or 10, as has happened to many earlier customers…

[@joebaucom4537]

Great !

[@ntblb89]

dual clutch doing 300 000 km and still in good condition , great engineering in that

[@floyddwayneviernum3816]

I like the custom snap ring tool. Did you make it, yourself? If not, where can I buy one?

[@speedkar99]

Canadian Tire

[@speedkar99]

Canadian Tire

[@historydude2743]

I’m looking at getting a 2019 VW golf sportwagen with the 1.8T FWD. any problems I should look out for?

[@speedkar99]

Maintenance and rust

[@calyodelphi124]

DSG is an initialism for DirektSchaltGetreibe, which is German for... Direct-Shift Gearbox. ;)

[@speedkar99]

Yes, direct shift gearbox

[@ganirao1980]

hello what will happen to the Dual transmission when drive is disengaged and moved to Neutral in around 90MPH speed ?

[@nikoz4841]

I own Acura TLX with 8 speed dct with torque converter. I do get confused moments on very low speed sometimes, but I love that transmission. Especially on the s sport mode when when it does rev matching downshift. It shifts faster then anything. Every time I drive my other cars, I realize how boring planetary based automatics are. And manual in no match either.

[@speedkar99]

DCT sure shifts fast! I wonder how different Hondas DCT is than this VW

[@trickster8635]

Where can I get one of those circlip removing tools?

[@speedkar99]

I got mine at Canadian tire, like 10 years ago

[@daviddillon172]

Dual cluch flywheels seem to fail quite often on manual VW's here in the Uk.

[@dantevito1193]

Then why do people use dual clutch flywheels on manual cars?

[@sergeantpeppers8858]

Engines AND transmissions? Is there ANYTHING the pointer brush can't tear apart?

[@liudas5377]

Can these dual clutch handle higher power?

[@waheedali2429]

Have you done teardown for Austrian ZF transmission

[@speedkar99]

Not yet

[@waheedali2429]

@@speedkar99 i hope you do it that will be a legendary teardown I heard ZF transmissions are the top notch best of the best

[@mustyali9529]

Please, I have a low speed whine when coasting from about 40mph down to about 20mph which i believe is coming from the transmission. What could it be? It's a 2006 Acura TSX auto. With 155k miles.

[@Cless9886]

You should do the infamous power shift dct from the Ford Fiesta

[@speedkar99]

I'd love to get a fiesta or focus DCT. I got a focus engine teardown coming soon though 🙂

[@joevignolor4u949]

Ford Powershift DCT's actually work pretty well and are reliable once the leaky input shaft seals are replaced with the updated ones and the oil soaked dry clutches are replaced. Ford created a nightmare for itself by manufacturing these transmissions and putting them in cars when they knew about the problems with the leaking shaft seals. I rode in one of these just today that was fixed at a Ford dealership three years ago and it works perfectly.

[@hedydd2]

The speed and frequency of shifts is far higher/faster than any normally driven manual gearbox. The shifts are done in the background up or down depending on the mechatronic logic, only actually engaging when the clutch on that shaft is engaged and on the old ratio’s shaft clutch disengaged. So there’s never a load on the shaft and synchroniser that are idle even though the synchroniser may shift several times before finally the clutch is used to engage drive on that shaft. The mechatronics working the piston that shifts the selector and therefore the next ratio up or down has no damper and the ram works extremely quickly and forcefully. I’ve bench tested these things using compressed air rather than hydraulic fluid and the changes are what most mechanically sympathetic people would call ‘brutal’.

[@jacobrobbins6181]

"It's not winter yet." LoL

[@speedkar99]

When it's winter I'm sure she'll be looking

[@matdcooke]

"It's not winter yet!" - PMSL! You have the driest sense of humour!

[@speedkar99]

Lol it's true... today was 18*C

[@Enigmaafk]

Nice 😊

[@speedkar99]

Thanks

[@dr.alangrant8969]

So where in the transmission does the power disconnect when sitting stationary but still in drive

[@speedkar99]

The dual clutches disengage

[@dr.alangrant8969]

@@speedkar99 so then the clutch engages again when releasing the break pedal?

[@joevignolor4u949]

@@dr.alangrant8969 That's correct. When you put a DCT in drive you don't get the usual lurch that you get when a conventional automatic transmission engages. Instead, as long as you keep your foot on the brake there is no power at all being coupled from the engine to the transmission. Then when you take your foot off the brake pedal the computer engages one of the clutches a tiny bit and the vehicle will start crawling along very slowly. Then when you push down on the gas pedal the computer gradually engages the clutch until it is fully engaged and the vehicle starts to accelerate.

[@simeon2851]

It just occurred to me you use everybody's old clothes to clean up the mess but yours.🙂🙂

[@speedkar99]

Yep that's how it works around here 😉

[@simeon2851]

@@speedkar99 Hahaha. Sneaky.

[@tossmonkey1]

Wish I was built as well as a dsg transmission

[@waifuracer6516]

Those clutches are likely original. These DQ250 gearboxes are very robust. My passat tdi just hit 193k miles (300k something km) and scantool reports plenty of clutchlife left. Car has full service history, the transmission is all original, even the dual mass is!! Which was shocking to see for me, having had multiple dmf failures on manual vws before. I drive my car very spirited and this gearbox is amazing. Never ever had any problems with it. Sometimes it can jerk a bit in heavy traffic, but its very occasional and only when you are messing around with the pedals, you kinda have to drive it with purpose lol. I loved driving manual but eversince i got a dsg i dont think ill ever go back. With flappy pedals it feels almost like a sequential. People are scared of these because "they fail a lot". The thing is, they only fail if you dont change the fluid. That will kill it for sure.

[@speedkar99]

Agreed. I think it's well engineered except for maybe the Mechatronic unit that might fail. But that's better than replacing the whole CVT 👀

[@waifuracer6516]

@@speedkar99 For sure :D

[@hamentaschen]

Dude. Like, Dude.

[@daveunbranded]

Is there a throw out bearing?

[@speedkar99]

No, because there's no clutch moving in and out like a manual transmission

[@daveunbranded]

@@speedkar99 the dual mass flywheel .. how does it know which clutch to use? 1 clutch needs to be released for the other clutch to engage and vice versa. How is that done? With the mech only? Neighbors car has a S4 Audi with shutter when he stops and in reverse. He doesn't get it when he shifts to neutral while stopping. Was not sure if it is his flywheel or mech unit.

[@Akotski-ys9rr]

Is there a difference between a dual clutch and a automated manual transmission? I thought it was the same

[@supersabrosinho]

Thought I was the only one who used an angle grinder as much as my 10mm socket

[@speedkar99]

I love my grinder too haha