Things You Should Know About Differential Gears

I made this video just before assembling my Ford 8.8 differential. I thought it would be a good idea to cover some of the basics before I dove into this part of the build.
One of the most important take aways from this whole thing is the difference between face hobbed, and face milled gears. They are set up differently and if you don't know what you have, you could make a lot of time consuming mistakes.
he best place for answers to your automotive questions: www.ericthecarguy.com
Camera: Brian Kast
Thanks for watching!
Discussion about this video: www.ericthecarguy.com/kunena/1...
Useful info
Ford 8.8 PDF: performanceparts.ford.com/dow...
A great book on Differentials: www.amazon.com/Ford-Differenti...
**Answers to your automotive questions found here: www.ericthecarguy.com/faq
Check out the series on my Ford Fairmont: • ETCG Gets a New Car! -...
A useful video on differentials: • Around The Corner - Ho...
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ETCG
Due to factors beyond the control of EricTheCarGuy, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. EricTheCarGuy assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. EricTheCarGuy recommends safe practices when working with power tools, automotive lifts, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video. Due to factors beyond the control of EricTheCarGuy, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Any injury, damage or loss that may result from improper use of these tools, equipment, or the information contained in this video is the sole responsibility of the user and not EricTheCarGuy.

[@spelunkerd]

I'm excited by this series. I have not found many good videos (yet) on the web showing how to adjust backlash and how to torque the pinion crush washer to specs. Great start!

[@ericthecarguy]

That video starts Friday. ;)

[@wingless95]

LMR.com has a good video on how to do it.

[@nick_callaghan]

Weber Auto youtube channel has good vids too

[@UndergroundTrev]

I can't wait to see your assembly video. I've had a set of 4.11's for about five years now and have yet to install them. I want to do it myself, but I'm nervous about messing it up. I haven't found many good videos about setting up rear diffs, but if anyone can give people the knowledge and confidence to do it themselves, it's you Eric!

[@joeconley1981]

This is why I'm a huge fan of this channel. Eric the car guy always has critical and very usefull info. Thanks Eric.

[@mybimmerspace]

As a formal greeting " Hello Eric The Car Guy" I can appreciate your dedication to educate; have seen quite a few of your videos . Just doing a Faced Hobbed 3.55 gear set on a Stang and came across your post. The original 5 cut faced milled gears versus the new edge 2 cut hobbed gear sets are pretty much the exact opposite when setting up patterns. I had to throw out everything I learned about setting up the face milled gears. Good point of figuring out gear ratio. Thank you for your dedication Take it easy...MBS

[@patw52pb1]

Nicely done. A lot of technical information in a concise format.

[@HsCSpanky]

Thanks for the PDF Eric. I'm not sure if I'll ever swap gears or axles but it's good info to have on hand.

[@korbenelements]

great info erick I loved it straight to the point no fluff.

[@Primer2toneGarage]

I like a little bit of fluff. 😁

[@StonnieDennis]

Great explanation!

[@TheStwat]

That's great info, Eric. Many thanks for that.

[@jayyoutube8790]

That was good...you have the rare ability of simplifying good info for all to grasp what you are saying... Liked the video too, gonna sub..

[@icurt06]

Thanks Eric. Great video short, concise and to the point. Great for us who suffer from ADD : )

[@ootdega]

I have a set of OEM Ford 3.08s on standby, and the ratio is cast into the side of the ring instead of the face of the pinion. Just wanted to put that out there. I learned a LOT from this. Both the video and the comments.

[@fooey88]

Learned a lot from this video. Thank you

[@greganagnostopoulos1958]

Great video Eric 👍🏻

[@adamcrombie]

Hey Eric! A helical gear set is made up of a ring (or crown) gear and pinion whose rotational axes cross. It looks like what you've got is what's called a hypoid gear set, since their axes are offset from one another. It might seem pedantic, but they are actually very different in their design... besides, we're all here to learn!

[@ericthecarguy]

It is. I got that part wrong.

[@youtubasoarus]

Awesome stuff Eric! :)

[@busilica123]

More videos of DIFFERENTIAL please. Interesting topic.

[@YXUHUNTER]

Great short video - GOOD Info! Thanks!

[@Adam-bw4lw]

LOL 13 hour ago WTF?!!

[@YXUHUNTER]

korai kiadás .... egyesek az tudja ... néhány várni kell ...

[@robinfocon]

well done Eric!

[@IntegraDIY]

Great video Eric

[@waltschannel7465]

Wow, excellent... especially the part about figuring out the ratios. I never got that but do now! 😁

[@24theMoney]

The road to hell is paved with good intentions. I watched ETCG epic 8.8 videos recently, what a battle! I paid a gear shop to install 3.55 gears into my 1992 foxbody. And you know what...decades later when I sold the gearset that was taken out...they turned out to be 3.55's all along! Hope Eric can feel better after hearing this. Cheers!

[@dozza202]

Great video Eric, I hope your planning on keeping the exterior and interior of the car stock, maybe a quiet exhaust, keep all that power a surprise lol

[@BurningRubberDC]

Hey Eric! Im loving the series and just got through all the videos from the beginning. Have you ever looked at MSD atomic efi? Its like a Carbeurator but its an efi system and im pretty sure it can be programmed for boost, diff stages of nitrous and so on.

[@CubasAutomotive]

from what I understand, ring & pinions should always be replaced in pairs. As in when replacing one, like the ring, the pinion should also be. Like shoes, they are a matching set.

[@ericthecarguy]

Yes, exactly.

[@LetsFixIT]

good info Eric

[@james072492]

MOAR of this differential topic

[@bleepinjeep]

Good vid Eric, lots of questions arise out of gearing! You said you bought those new but I hope you were confused cause they looked a little worn out, lol.

[@ericthecarguy]

True that. Yea, they were new, just covered with rust inhibitor is all.

[@theGAUSIN]

Just installed 4.10 on my n/a cobra and it made a huge difference. Woked the car up and it pulls hard .

[@HarryTwatter]

same here on my ls1 it's a world of a difference, pulls hard!

[@wyattoneable]

Thanks Eric.

[@spunkmire2664]

I just cleaned up and painted my nine inch diff for my '64 Tbird. Been really thinking of saving for disc brake conversion.

[@ericthecarguy]

Do it. It looks so cool when it's done.

[@spunkmire2664]

thanks for the vid!

[@godfreypoon5148]

You want to tell us all that about differential gears? Well that's just your pinion bro.

[@zx8401ztv]

Nice :-D

[@WreckDiver99]

I'll PINion him down for you!

[@TheBrokenLife]

WreckDiver99 These puns are really starting to grind my gears.

[@WreckDiver99]

Maybe you need to shift your thinking a bit.

[@TheBrokenLife]

WreckDiver99 Do you think that would have a *bearing* on my attitude?

[@j.r.3330]

Great vid

[@braydonlill9708]

@EricTheCarGuy im going to need a part number on that black t shirt... it just looks comfortable

[@duanebonney]

Thanks for that info, Eric. When I had a new custom Driveshaft put in, I noticed a whirring noise around 35mph. Do you think that my installer may have knocked my pinion out of wack, causing the noise?

[@UniB4ll]

Eric, I can't thank you enough, If I could give you more than one thumb up I would. Thank you for sharing your great knowledge and this and all your videos! Be safe, have fun and stay dirty my friend.

[@ericthecarguy]

You're most welcome. Thanks for the comment.

[@kcg795]

I had the differential rebuilt on my 84 Toyota Van at while back. Since then, it seems quiet when it's under load, but makes a whirring sound when I'm coasting.

[@justhes]

I had that problem with my ford 9" after I put my factory gear back in. I had to adjust the pinion depth by a hair and the noise went away.

[@kcg795]

The shop that rebuilt it said they put everything back into spec too.

[@superrodder2002]

I think the backlash is set a little to loose and that's causing the gears to whir when coasting.

[@DELTRANIO99]

Eric thanks for all your videos ,,BTW what brand ring gear and pinion do you buy ?

[@SmittySmithsonite]

A great way to remember that ratio formula in the correct order is, "Driven divided by drive". Say it out loud a few times - you'll never forget it. :)

[@CreateYourWorth]

awesome!

[@ComblessMan]

OK, I did my searching and now I have a question. I know about gear ratios from engine to transmission. I get that. I understand how they relate to the differential. What I don't understand is how the gear ratios of the differentials relate to performance. I don''t get the number. I think the number relates to the rotation of the drive shaft and I believe the top number, for example only, the ratio is 3:1, the top number is the rotation of the drive shaft the bottom the axle. And, if that is correct, how does that relate to performance vs just normal street driving. Would it be advantageous to have a say, 1:1 ratio for racing or for pulling tree trunk from the ground? Just wondering. I really couldn't find anything definitive. Thanks.

[@lemeister3032]

Hey Eric, my dad's 2006 Audi A6 has a problem with AC, driver side vents are heating while the passenger side vents are cooling... Any advice? BTW love your vids

[@jett4777]

Diff gears or just gears in general, are craazaay

[@MrA1Goku]

Good to know

[@billymonkey111]

Comment numebr 2! Cheers eric, no one will ever beat the 1950s Pathe film about diffs though

[@zx8401ztv]

That was a brilliant way to learn :-D

[@ericthecarguy]

That is a good film.

[@ericthecarguy]

BTW it's linked in the description.

[@Tugboatpb]

What would cause a differential to explode or be noisy? What aspect of setup would cause those results?

[@Unmentioned77]

Eric you said in the tear down video that high gears are stronger than lower gears. Cause then pinion gear is larger. What about with trucks and towing? Lower gears give you more torque. Usually trucks with lower ratio have higher towing capacity. Your thoughts?

[@ericthecarguy]

Trucks have larger gears to begin with.

[@mrsemifixit]

I thoroughly enjoyed this as someone who doesn't know much about differentials. Thanks man

[@iHaveBeenBaffled]

The 8.8 on my '96 f150 just leaked all the gear oil out, now she howls & clanks, already have a new rear end to throw under there when she goes

[@abhiramholla2221]

Hey Eric, I want to know..Will there be a loss in spider gear in differential due to it's free rotational movement?

[@sandman1624150]

QUESTION::::can you ever use the pinion with another ring or do the always have a set pinion and ring???.? Hoping for an answer...thanks

[@BruceWayne-kx5qs]

What gear pinion set would you recommend for a 94 Chevy Silverado 350 with a TBI, I need more power on the high end. At 70 MPH I am at about 1400 rpms.

[@laitha.m6888]

Thank you so much ...I have question please my car turn 120km and rpm 3,5 engine 3000 v6 manual ger Galloper what is sort of corona which high speed better once you advice ?????

[@robertporter6410]

Mr. Eric if you currently have a good pinion bearing in a 8.5 Chevy but have serious slack in your carrier bearings can you just change out those bearings and use same shims and your done or do you still need to set backlash?

[@TheOGMexicanMonkeyz]

Should I cheap out on a ring and pinion set looks like I can get one for my truck on Amazon for around 200 bucks or I can get one off summit they’re set up looks better

[@behelpful1435]

Why have these two manufacturing styles (milled/hobbed) of gears for differentials? Is there different applications/purposes for each type?

[@kavitamaraj1671]

Good day Eric, what is the ratio on a Toyota Hilux LN166 rear differential and on a Toyota YN106 4×4?

[@robgrune3284]

are aftermarket covers such as afe beneficial?

[@jesseduke694]

I am just now taking a interest in gears & diffs. I have a very good understanding of engines. And a general understanding of differentials. I have built engines, but I have never built a diff. I have had a couple built. I have taken apart c clip diffs far enuf to change all the seals. Just never built one. I have a couple old trucks & one has a 8.8 in it & the other is a 10.25. Im thinking of welding the spider gears so they are locked. Would it be best to stick weld or mig weld?? I wasn't sure if they were cast gears or not?? Im curious what the rear-end dous if a weld were to ever break loose??? Is just open or dous it leave me stranded??

[@7710747]

Eric, I need to know who makes the best pinion gear sets as i have to rebuild my 98 Dodge Ram rear end w 3.55 ratio. Who are your top 3 please

[@AnaAna-cj1xs]

Hi Eric, how to change gear ratio for higher torque?

[@cancer_stixx]

Id be keen to see a video about re shimming a viscous style LSD if that could happen some time in the future!

[@ericthecarguy]

I still have the old differential. I hope to to a break down video of that at some point.

[@franciscosotelo1866]

What brand do u recommend for a 2017 Gmc 3500 hd . Yukon, us gear , g2 etc.....iam putting 4.56

[@bojanglez4855]

Sooo what's way to go to go faster. Big question I need answered

[@edwintorres5850]

HI Eric, when you take the dial reading for backlash you take it on the drive side or coast side?

[@gavincline3581]

Tell us about the limited slip portion of it.

[@The88katana600]

nice thanks

[@MrNotorius5500]

Eric you said those were helical gears. Correct me if I'm wrong (which I usually am lol) but aren't those really hypoid gears?

[@jabawokidingdong1360]

I believe they're helical-bevel gears. But as with most tech as old as the cog itself, most combinations have been attempted. As a result, sets of varying gear types are labeled differently than the independent parts which make the set. Just as with a "rack and pinion" Basically 6 one way 1/2 a dozen the other

[@isaaccastillo2630]

helica gears are the teeth slanted at an angle (heel to toe aren’t inline if that makes any sense) the reason why they shape them like this is for noise reduction

[@Kevin-is-here]

Eric have a quick question, have an 87 f150 with a manual 4 speed & wanted to change the gear oil but I can't see a drain plug for the life of me, any advice would be greatly appreciated, thx

[@ronaldoswald1942]

Ratio is stamped on the ring gear.

[@micsor4121]

awesome

[@vetterfellow]

Very nicely done Eric. continue this great stuff. Stay DIRTY... Angelo

[@NebukedNezzer]

My father was a machine design engineer. He hated the Hypoid gears for the inefficiency they have(part worm gear). One of the good things about front wheel drive cars is NO hypoid gears.

[@rotekkable]

Hypoids are noisy as well within certain ranges. Ford's 3.73 and Toyota Tacomas have em and everyone bitches about bad differentials.

[@MOSTAFIZURRAHMANtungsten]

How to know the piston position in cylinder?

[@Ashroyer86]

If most gear sets are face hobbed then just about all of these instructions and charts online are misleading people. For instance the pattern on the drive side is high on the face towards the heel and the instructions say to add shims to the pinion to move it closer to the ring's centerline. Here's the issue, those instructions are correct, but correct for face milled, not face hobbed. And those instructions are what pop up just about every time you do a search on ring and pinion patterns. Therefore assuming that just about everyone is using face milled gears not face hobbed like you say most gears are. This is important to me because I set up my rear and the pattern should have been close enough but over a few drive cycles started getting more noisy, after tear down I saw where the pinion is riding too high and too far back on the drive AND coast side so today I had to spend a good amount of time learning the differences in milling so I can adjust accordingly.

[@kcube1000]

what if i use 1:1 gear ratio on ring & pinion gear ratio. ?

[@BigHappysPlace]

I don't recall. Was this the rear out of the pony? Or out of Oliver? 2.73 sounds more like what the fairmonts had in them.

[@ericthecarguy]

I got this differential from Pull-a-Part. Separate from both cars. The rear in the Mustang was hacked up pretty good and I couldn't use it.

[@adamelektronik21]

Could your watermark be smaller, Eric? Anyway, great videos, keep up the work!

[@ericthecarguy]

No.

[@mitchsfarm]

We make these at our plant! Both gears we process. We heat treat the pinion gear, and cut the ring gear. Thats funny ahah!

[@Mohamedseddek]

♥️♥️♥️♥️

[@victorpla16]

Can you explain to the public the difference in Gear Ratios and The Benefits and Disadvantages

[@ericthecarguy]

High gears=high speed at low rpm but slow take off. Low gears=faster take off but compromise top speed.

[@sldpf2113]

+EricTheCarGuy is there a sweet spot to get them both ?

[@nos1000100]

that all depends on the power output of your motor and what you want the car to do

[@camperpro482]

I have 3.42 common in gm

[@donaldhollums3278]

"Oliver"? Did you consult Richard Hammond from Top Gear UK about naming your car after the name he gave his car on the African road-trip episode? As a matter of fact Hammond's car was the same color as yours.

[@ericthecarguy]

That's one of the reasons I chose the name. I also chose it because I seem to have similar affections for my car. If I run into Richard, I'll be sure to buy him a beer and perhaps throw him the keys so he can take it for a drive.

[@archiguitarchi]

I'll be happy to share my personal knowledge about differential gears: They are a PAIN IN THE ASS.

[@bluecollarjose]

Oliver!

[@jevaughnbullard9203]

What does 8.8 refer to

[@bolognablake]

Eric, I've never seen a calculator that dirty.

[@Goriaas]

isn't a 2.7 final drive super low? like pretty much only good for coasting on the highway?

[@BigHappysPlace]

yeah provides low rpm for better MPG.

[@ericthecarguy]

2:73 is actually considered a high gear. 4:11 would be a low gear but you have the premise correct.

[@FrenchValleyAirport]

4:10s in my S2000 eric :)

[@randybehrmann5454]

I have had one vehicle with a 2.56 ratio and one with a 2.28 ratio. Those types of ratios were common before overdrive transmissions were the norm, outside of performance cars.

[@HarryTwatter]

had 4.40 in my old EM1 haha that thing was at 4k doing 70mph

[@SuperWishaniggawoods]

Literally just paid 1800 to have my whole differential assembly replaced. Now I’m still having issues when I break . The truck jerks and then when I was driving on the street it started to make that sound like it was about to break down again, I started pressing on the gas and it was going no where , so then I attempted to pull to the side of the road then it started working again. Call me crazy but I’m kind of pissed off right now

[@Brian-Burke]

Captain Obvious analysis here, but damn, Eric you know a lot about cars. Impressive.

[@ericthecarguy]

I could still learn a whole lot more, but thanks.

[@ABs70nova]

I know a wayyyyyyyyyyyy easier thing to when trying to figure out what gears you have in the back. Lift the rear end. Put vehicle into neutral Mark the driveshaft with a line. Mark the inside of your tire with a line. Spin the tire slowly Count the number of times the driveshaft does a complete 360 in relation to the tire Example. I have 3.73gears so my driveshaft spins 3.73 times for the tire to make 1 complete turn

[@Awayze]

Did you study engineering? As a mechanical engineering student, they didn't go into this much depth into gears.

[@David-yy7lb]

Another thing to mention is the lower the gear ratio the less teeth on the pinion gear and the weaker the pinion gear gets

[@joeysmama8701]

That was the dirtiest calculator I have ever seen..

[@ericthecarguy]

Still works. :)

[@Primer2toneGarage]

It's staying dirty. Lol

[@chrisdiana3525]

what do those ratios mean?

[@spelunkerd]

3.54 means that the drive shaft turns 3.54 times for every full revolution of the ring gear. The design of the transmission is based on those ratios so changing the diff ratios will change the ratio of engine rpm to vehicle speed at each gear. What I find intriguing about the design of the differential was how they offset the pinion to allow the cab to have a minimal hump where people like to rest their feet.

[@chrisdiana3525]

thanks for the reply. Makes sense.

[@fpvgtking]

Basically how many rotations the piñon does in order the cover one single rotation of the ring gear, it can be calculated using the number of teeth, diameter (which is a little harder in this case) or linear velocity on at the centre of the tooth diameter (which is also a little harder to do)

[@MrNotorius5500]

Yeah it's called hypoid.

[@Jacksonkellyfreak]

So no more tool reviews?

[@ericthecarguy]

I've taken a break from those for a bit to come up with something else.

[@Jacksonkellyfreak]

Oh :( Loved your reviews and was hoping to see some more air tool reviews since you got that awesome compressor. But whatever you come up with I'm sure will be great.

[@ericthecarguy]

I'm not doing away with them completely, I'm looking for a way to present them differently. I haven't sorted it out yet so in the mean time I'm going to focus on Fairmont Videos until I figure that out.

[@Jacksonkellyfreak]

EricTheCarGuy Ohhhh I gotcha now. Well that's gonna be awesome and I can't wait.

[@jett4777]

But they are interesting

[@MrToerman]

Eric, those are actually spiral bevel gears, not helical gears.

[@franciscargo321]

What combination transmision and deferential to 4dr5 engine.

[@maingun07]

So why is it called an 8.8?

[@itsnotan8]

I'm pretty sure that's the diameter of the ring gear.

[@maingun07]

Wesley Young Thanks

[@ericthecarguy]

Funny, I realized I missed that in this video and mention it in later videos in this series. 8.8 is the diameter of the ring gear. That's how Ford identifies their rear ends.

[@maingun07]

EricTheCarGuy Thanks. Look forward to watching the rest of the series.