Understanding Differences in Automotive Differentials

See 11 different types of automotive differentials and learn how they work. This video is intended for students in the AUSV 1220 Manual Drivetrain class at Weber State University with Professor John D. Kelly.

CORRECTIONS:
1. The differential I called a "Detroit Locker" is not a Detroit Locker. It is just an Eaton Posi Limited Slip differential. A Detroit Locker uses dog teeth and is a truly locking differential. Thank you goes out to Keith MacDonald for catching my error.
2. I did not adequately explain how the clutch packs of a limited-slip differential are applied. The simple rotation of the side gears versus the differential pinion gears does not cause clutch packs to apply, otherwise, the clutches would apply when turning corners at low load (low torque). Torque from the engine (or another propulsion source) is necessary. The more torque you supply to the differential side gears the higher the force on the angled (ramped) teeth, the higher the force on the clutch packs. Thank you to several viewers for pointing out my omission.
4. I incorrectly described the operation of the original 1956 Dana limited-slip differential. The pinion pins on the original Dana differential have tapered ends. The pins sit in four V-shaped ramps in the differential case. Under a load, the differential case applies rotational torque to the pinion pins causing them to slide up the V-shaped ramps. This action applies outward force to the side gears and the clutch packs. Thank you to several viewers for pointing out my error.

TIMELINE
0:00 Start
0:08 Introduction
0:32 Open Differential
3:55 Power flow through a differential
6:51 Side gear backlash control
9:09 Differential Demonstration
10:21 MUST SEE Differential Equations
13:12 Automotive differential history
14:44 Dana Corporation's 1955 invention of the automatic locking differential
15:33 Various names for Dana's locking differential
17:23 See a 1963 Chevrolet positraction differential with clutch packs
24:00 How rotating gears apply a clutch pack
26:35 Why limited-slip additive may be required for a clutch-type differential
28:46 See a 1970s era GM positraction differential with clutch packs
29:40 See a 1984 Chevrolet Corvette Limited-Slip differential with clutch packs
30:02 See a 2012 Eaton Posi Limited-Slip differential with clutch packs
34:00 MUST SEE See a worn out 2010 Chevrolet Camaro SS Limited-Slip differential with clutch packs
38:00 See a broken 2005 Jeep Wrangler Rubicon Torsen Type B style limited-slip differential with an air locker
43:51 MUST SEE See the pieces of a Torsen Type B style differential and see how it works
48:03 See a 2002 Toyota Tacoma Electric Locking Differential
51:00 See the Eaton Detroit Trutrac (Similar to the Torsen Type B differential design)
49:55 See a spool with no differential action
53:40 See a Mini-Spool and how to install it
56:35 See the Eaton Locker and learn how it works
1:00:45 Final wrapup

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[je]

My Dad retired from Dana as an engineer and I never thought that was cool until now. This video was fascinating. Thanks for teaching.

[kmgb]

A truly excellent instructor. His students are privileged to have the opportunity to learn from him.

[karlx-]

No matter how much I think I've learned, The Professor always teaches much more, and in-depth. A natural teacher with great pace for complete absorption.

[smid]

It's a pleasure to watch a video by someone who knows WTF they're talking about. Even though it's over an hour long, it seems much shorter because he makes it interesting and informative; no stupid music or attempts to be a comedian. Classy and well done +++

[pierrec]

Man, this channel can't ever be boring with this much knowledge shared to you.
Some of my friends find it funny how I talk about differentials a lot but they don't know how much goes into it 😂

[kahnfused]

60 years this has been a mystery to me. This was the most comprehensive explanation I've ever seen. I still don't own a thorough understanding but it makes more sense. Thanks for taking a great deal of your time to share this.

[TheTexican]

Can we all pause to appreciate how lucky we are to have this content available, any time, for free? 🙌

I wish I’d known about this channel long ago. It would have allowed me to better educate friends and customers in the car world.

Thank you to the crew and Professor Kelly for putting these videos together. 🍻

[mikemidulster]

All of the animations on the internet put together would not substitute for a great teacher like this. Professor Kelly predicted every possible question of how differentials work and left no ambiguity.

[Wuffenberg]

That was an EXCELLENT tutorial! No stupid music, perfect camera, lights, mic sound! And very sympathicly presented. Many thanks from Germany! I learned a lot from it.

[Slider]

I love these videos. I've spent years (~35) trying different differentials in street cars, road racing cars, LD trucks, HD trucks, snow plows, off-road vehicles, etc. and it is nice to see someone who understands how they work.

I don't know if you noticed though, the different ways that the clutch packs are applied in the limited slip differentials (LSDs) shown. In some LSDs, like the 1st one shown from the 1960's, it is the torque applied to the ring gear and the pinion cam profile that proportionally clamps the clutch packs together. For racing this is preferred over the spring preload LSD style. On the other hand for street use in icy and snowy conditions a spring preload LSD tends to perform better. Both the driving experience and how they function is unique to each LSD style. I'll explain below why.

If you look carefully at the 1960's LSD you have and pay special attention to way the spider or pinion cross shaft sits in the differential housing you'll notice it rides on an angled cam machined into the housing. As torque is applied to the ring gear (and hence the differential housing), the pinion cross shaft rides up the cam and this creates the separation force that clamps the clutch pack together. There is still a separation reaction force generated by the spider and side gears, but the majority of the clamping force is due to the cam.

These cam or ramp based LSDs can typically be purchased with different cam angles (not sure about the one from the 1960's). Some have replaceable cams, while others you have to machine (or purchase) the housing with the angle you want. The purpose of this is to adjust the amount of differential "lockup" you get per amount of torque applied. You can also create a different amount of lockup for the forward torque (acceleration) vs reverse torque (deceleration) by using different cam angles for each direction.

The Torsen style differential bahaves functionally similarly to a cam applied LSD, but the downside to a Torsen is the forward and reverse torque induced differential coupling cannot be individually tuned as easily. Most people claim Torsen's can't wear out, but I can confirm they definitely can.

Many modern limited slip differentials used in street cars (like most of the LSDs in the video) do NOT use a cam profile to apply the side clutch packs. Instead they use a less expensive spring's preload to create the majority of side clutch clamping force, combined with the spider/side gear separation reaction force. If the driver simply wants to be able to perform 2 wheel burnouts or drive in the snow, this style can work well.

Detroit Lockers are another story (note in the video the LSD labeled Detroit Locker was not a Detroit Locker). They are not really differentials in the classical sense, nor are they LSDs. If you imagine taking a pair of ratchets from your toolbox, cut off the handle, and weld them to each side where the side gears normally go in a differential, you have created the function of a Detroit Locker. For straight line driving, both wheels turn at the same speed so the ratchets work fine. When you want to corner in good traction, the outside wheel wants to turn faster so that side's ratchet will allow this to happen while going "click, click...". The coolest part of the Detroit Locker is when you switch from drive to reverse and vice versa there is a bit of a clunk (and the driveshaft will turn 1/4 to 1/2 a turn). What this is doing is switching directions for the "ratchets". The direction of torque applied to the ring gear is what selects forwards or reverse for the ratchets.These work great off-road, in snow plowing trucks, and in heavy, long wheelbase vehicles.

Eaton Gov-Loc's are a bit controversial and are poorly understood in general (the video did a great job explaining them). Most people I know hate Gov-loc's because if you rock the vehicle from forward to reverse to forward to reverse to..., spinning the wheels each time, you'll destroy a gov-loc in no time at all. Where I've seen them work very well is when used in a heavily loaded truck and one tire is on ice and the other is on pavement. No common LSD will lock up enough to get anywhere close to spinning the wheel on pavement. With a gov-loc, if you are gentle on the throttle, the governor will engage, the clutch packs will tighten more and more until the differential is effectively locked up, and the truck will simply drive ahead (or will start spinning the tire on pavement, even burning rubber with a heavily loaded truck, if it is stuck badly enough).

With modern vehicles there is another option that most vehicle manufacturers are starting to implement with varying degrees of success (sometimes combined with viscous coupling differentials). This option is to use the ABS system to create a virtual locker. The software monitors steering angle and relative wheel speed (all 4 wheels). If programmed well, the instant a wheel starts to spin, that wheel's ABS engages and slows the spinning wheel down to the speed it should be turning. What I like about this option is every single vehicle sold today has the ability to include virtual lockers, essentially for free. All it takes is a bit of software to use the already present ABS system as a locker and by including drive by wire it becomes a seamless addition.

[partykeeps]

We live in a fascinating era with amazing new technologies but looking at automotive inventions of the past is equally amazing.

[flatus]

Instructors like him make things simple and interesting… I bet his students go out to be excellent mechanics…. Thank you Professor Kelly!!!

[julianharms]

I probably shouldn’t have started watching this when I had work to do! Such a clear explanation and I now properly understand how locking differentials work. Lucky students - you have a great teacher!

[WeberAuto]

CORRECTIONS:
1. The differential I called a "Detroit Locker" is not a Detroit Locker. It is just an Eaton Posi Limited Slip differential. A Detroit Locker uses dog teeth and is a truly locking differential. Thank you goes out to Keith MacDonald for catching my error.
2. I did not adequately explain how the clutch packs of a limited-slip differential are applied. The simple rotation of the side gears versus the differential pinion gears does not cause clutch packs to apply, otherwise, the clutches would apply when turning corners at low load (low torque). Torque from the engine (or another propulsion source) is necessary. The more torque you supply to the differential side gears the higher the force on the angled (ramped) teeth, the higher the force on the clutch packs. Thank you to several viewers for pointing out my omission.
4. I incorrectly described the operation of the original 1956 Dana limited-slip differential. The pinion pins on the original Dana differential have tapered ends. The pins sit in four V-shaped ramps in the differential case. Under a load, the differential case applies rotational torque to the pinion pins causing them to slide up the V-shaped ramps. This action applies outward force to the side gears and the clutch packs. Thank you to several viewers for pointing out my error.

[TheTravellingHobo]

Probably the best and most educational video out there for automotive differentials

[Filmpilot]

You’re obviously teaching a trade school how lucky are your students to have somebody who can explain this so succinctly bravo sir.

[MrPatdeeee]

You know John, that in 1947 I learned differentials in auto shop. And of course, the teacher told us they were "spider" gears. And it always happens that when you learn something when you are young, it tends to cast into cement. If'n you git me drift! LOL

Thus, for 70+ yrs now, I always had a problem when someone says other than "spider" gears when talking about differentials..

But I will tell you this kind Sir; since I believe truly that you are one of THE greatest teachers I have ever had; so I will stop having" that problem"; and say something I would never have said, if I had not met you. LOL

Thank you John. You are truly a cut-above. As an 89 old man, I love your YouTube video's. Among THE best IMHO. Keep up the great work.

[Calico_on_oaw]

Finally making it to 65 years has me relearning anew. Professor Kelly, you remind me of one very special mentor, Scott Towsly, who helped me as I struggled during my early learning years. Thank you for being so thorough. I did know some of this lesson was not exactly the correct terminology but knew viewers would be helpful pointing to that. Just the amount of info you brought was plenty tough enough. I'm impressed.

[donnlowe]

I'm 75 years old and I've heard of all these different types of positraction rear ends But it is really nice to have the differences Explained in such detail.. Thank you.

[tomrandall]

Nice refresher course for us old school guys! Oh the tales of the stuff we did in our youth!!! 🤣