How Clutch Type Limited Slip Differentials Work

[@CosineHyperbolic]

Awesome video- probably the most detailed I've seen on clutch LSDs. That said there's a few things I would have touched on- just in case you ever do a similar video, maybe elaborating on differentials: It helps to consider four cases when thinking about the behavior of [helical and clutch] LSDs (viscous coupled LSDs are indeed as simple as you describe, so there's no need for elaboration)- engine acceleration, engine braking, wheel braking, and coasting in neutral. Thinking about LSDs through this lens helps clear up some confusion; if I understood correctly, you seemed to imply clutch (and maybe helical) LSDs lock due to wheel speed differential, but that's actually only true for viscous coupled LSDs- for example clutch LSDs experience lockup on acceleration regardless of wheel speed differential (like the picture at 4:50 shows; the torque from the engine rotating the case pushes the cams apart, compressing the clutch packs), and they won't lock up at all if you're coasting in neutral, no matter how tight you turn. The boiling down of these four cases into two (accel/decel) is what causes the most widespread confusion of all regarding clutch LSDs- what happens under [wheel] braking. A 1 way clutch LSD does not lock under engine deceleration (engine braking), but it DOES lock under WHEEL braking (yes, 1 way!); this is because the relative motion of the parts involved in lockup actuation is identical whether accelerating or [wheel] braking, so there is no possible way for the device to lock on acceleration without also locking under [wheel] braking. What 1.5 and 2 way clutch LSDs add with the second ramp angle is locking under ENGINE braking specifically. I couldn't quite tell if you were aware of that- though the vehicle behavior you described does line up (like you said, a 2 way clutch LSD will basically always be locked up, because in the context of racing, you're always in gear, either accelerating or engine braking). One more nuanced subject here is the difference in lockup between helical and clutch LSDs. You clearly mentioned how helical LSDs don't really interfere as much as clutch LSDs tend to in terms of understeer, but as I mentioned above, they do actually activate in response to engine torque, not wheel speed differential- so why are they so much "calmer" compared to clutch LSDs? Two reasons. One reason is that even the more aggressive helical LSDs have a torque bias ratio (4:1) capable of only a 20:80 torque split (that's equivalent to reducing the clutch LSD friction surfaces down to 80% lockup), so they can never lock as much as a common clutch LSD (which you mentioned); the other reason is that, while I mentioned all clutch LSDs actually lock under wheel braking, helical LSDs do not (though on that note, they do unavoidably lock under engine braking the same amount as under acceleration, meaning all helical LSDs are "2 way" LSDs, in a sense). Here's a random cheat sheet on differential lockup activation scenarios (I posted it in the context of WRXs): i imgur com/OCI6wpY png Differentials are absolute BLACK MAGIC and I love it. Hope this doesn't come off rude; I wanted to write things in a way random people who find themselves here may be able to follow. Keep up the awesome educational content! [edited to improve clarity]

[@justwant2watchvids]

Was wondering if you could update the imgur link as I couldnt open it with a google search

[@dontwatch1227]

This is what I was wondering. I prefer increased lock during engine breaking to increase exit speed

[@187Burks]

Keep making content!! PLEASE keep the videos long and informational. Love the mechanics and engineering behind products like this. EXCELLENT VIDEO

[@FlatironsTuning]

Thanks very much! We are short on time here recently but we definitely have a lot more that we want to touch on. Stay Tuned!

[@dhwin5709]

Now I finally have a full understanding of how the CLSD works! Much appreciated. Thank you for making this video

[@FlatironsTuning]

Very glad it was helpful! Thanks for watching and Stay Tuned!

[@ITProjectManagerMan]

I found this very helpful to understand how I could solve a setup issue for sim racing (Project Cars 2). Was having issue with getting around slow corners in a Porsche 917/10 (1972 Can-Am Car) at Spa. In real life the car has a Locked Diff that is great at putting the cars 1100 hp to the ground but not good for getting around slow corners, I changed to a Clutch LSD with 10 Clutches, Preload 80nm, 75 deg power ramp, 45 deg coast ramp. I was immediately a couple seconds quicker and with more consistent lap times. Thanks for the tutorial.

[@FlatironsTuning]

That is awesome Jeff. Glad that this was helpful for your understanding. Thanks for watching and Stay Tuned!

[@cosmic_gate476]

I am so glad the new Z is coming with a clutch type rear diff. I'll be driving it year round in Canada. Thanks for explaining the difference.

[@FlatironsTuning]

Glad that this video was helpful. Thanks for watching and Stay Tuned!

[@yowie0889]

Great video. I can also confirm that the podcast is great with its perspectives from people who build & race cars on limited budgets.

[@FlatironsTuning]

Thanks for the comment, and thanks for listening. Stay Tuned!

[@jamesleahy3048]

Excellent information thanks so much for making this.

[@FlatironsTuning]

You bet! Glad it was helpful and thanks for watching. Stay Tuned!

[@1974mazdarx3sedan]

nice one, thanks. fully understand the 1/1.5/2 way, ramp angles and the pre-load now. it may as well have been wizardry before. i have a 2008 Sti r180 lsd on the rear with a clutch pack that i've broken on the same tight corner twice. i've been recommended to go for a Cusco. i have questions now for my shop for how we're going to setup the Cusco. if i can stay on the track with this i'll start looking at the front lsd.

[@FlatironsTuning]

That is fantastic to hear. Very glad that the video helped! For the rear, generally speaking, a 1.5 way with full lock is a really good starting point. The front, that is another story all together. Lots more to consider there. Thanks for watching and Stay Tuned!

[@xtangent1846]

Excellent

[@FlatironsTuning]

Thanks for watching and Stay Tuned!

[@crpreludeh22]

Wwwoooo, this video is really good, there was a lot of info that I didn't know. Thanks for this awesome video 👍😀

[@FlatironsTuning]

That is great to hear. Thanks for watching and Stay Tuned!

[@johngraham1037]

Yet again Jon, another very informative video. LSDs always make my brain hurt and I could never see how they worked. This definitely cleared a bit of the fog. It's now just hiding behind some mist.

[@FlatironsTuning]

That is awesome John. Glad to shed some light and Stay Tuned!

[@jeffersonrodriguezvera2732]

this help me a lot this video right now im trying to setup my clutch lsd for my personal use thanks

[@FlatironsTuning]

That is great to hear. Glad you found this video and thanks for watching. Stay Tuned!

[@AlexMotoCy]

Great video great content keep them up I love them and so helpful

[@FlatironsTuning]

Thanks for the comment. Lots more to come so Stay Tuned!

[@miguelgerardtan7319]

Hi there, very informative video.. i drive a daily altezza with cusco rs setup 1 way at 100% but under corner liftoff it jerks.. question is with minimum of 6 springs for preload will it solve the corner deceleration lockup when I liftoff Or am i better off with a torsen 🤭?

[@umutooo]

Great video. What is your suggestion about Sg5-Sg9 Forester XT 4eat-VTD Transmission with Rear Viscous Lsd? Stock Lsd is weak. What type of lsd is best for my XT? For use mostly on the street and in slippery conditions.

[@devbhavsar5113]

hey very nicely explained, can you tell does the pre load or the pressure springs are always needed in this differentials or it can run without it also properly, and also does the gear ratio also affects any things ( the main axle shafts gear and the pinion gears ) like should it always be in 1:1 or it can differ

[@djthombomb7554]

Funny Freudian Slip at 8:40! 😁

[@benjaminhowe4290]

I believe on the 06 STI the rear diff is a clutch type LSD.

[@FlatironsTuning]

I just double checked, and you are correct. Was off by a year on the rear diff :-) Stay Tuned!

[@HeidiFegles]

I will be doing some serious experimenting on the 07 jdm 4:44 wrx trans with lsd read and open front. And center diff is not strong enough lol. So I will be shimming the clutch packs by .020 at a time untill I achieve almost locked

[@RobHTech]

I don't understand what exactly happens in a 1.5 or 2 way under deceleration/braking. I suppose that if a 1.5 way, under braking/decelerating that if one wheel is slowing down faster than the other that the diff will then equalize the braking torque between the wheels? But, wouldn't that upset the car? Or like why would you want a 1.5? And, if it's say a street car, does it even need a 1.5 or 2 way? Except I'm interested in the VB rear diff, not the front. I'm thinking to put the Cusco RS into the rear and keep the front and center diff the same.

[@FlatironsTuning]

Thanks for watching and thanks for your question. Yes, with the 1.5 way or 2 way, the diff will lock up if there is wheel speed differential. The 1.5 way will do it slower, but the 2 way will do it faster. In the rear, it doesn't upset the car, it actually helps keep the car going straight. Now if you are turning and let off the throttle aggressively, that can cause the rear to start to step out. This is more the case with the 2-way, and that can be one of the reasons that you would put a 2-way diff in your car, so that you can get the car to rotate by coming off the throttle. For a street car, I'd say the 1.5 way would be better than the 2 way. In the rear you will miss out on some rear stability under braking, so the 1.5 way does tend to be the best fit. Hope the helps and Stay Tuned!

[@jcasey460]

nice informative vid. Thanks

[@FlatironsTuning]

Thanks for watching, and glad you liked it. Stay Tuned!

[@flyingmr2]

Any input on a clutch lsd in a synchronized transaxle? I was told that it’s asking for trouble.

[@FlatironsTuning]

Thanks for your question. We have been running clutch diff's in synchronized transmissions for a number of years with no issues. The main thing you have to consider is the fluid that you use. You need something that works with the synchros and the clutch diff, but companies like Cusco have oil designed for that. Hope that helps and Stay Tuned!

[@flyingmr2]

@@FlatironsTuning thanks for your reply! I just purchased a Kaaz unit for my MR2. I will consult Kaaz on what fluid/additive they recommend for my application.

[@FlatironsTuning]

@@flyingmr2 That is the best place to start. And I think that Kaaz has a recommended fluid.

[@rikomanaro]

What would be a good preload and lock setting for a rear sti cusco type rs lsd, if you’d only like the car to have a controlled shallow angle slide behavior after initial breaking and turn-in?

[@FlatironsTuning]

Thanks for your question. Generally speaking, in the rear, you want as much lock as possible, so we typically leave the Cusco rear diff's set up as they come from the factory. The front diff is where the set-up changes make the most difference to the behavior of the car. Hope that helps and Stay Tuned!

[@gerik3343]

for thr clutch plates locking do i need to do both sides? or just one side when adjusting it to a 80% locking

[@FlatironsTuning]

Thanks for your question. If you are stacking two clutch plates together to reduce the amount of locking that they provide, you would need to make that change to both sides of the differential. Left and right equally. You would not want one wheel to have more lock potential than the other. Thanks for your question and Stay Tuned!

[@gerik3343]

@@FlatironsTuning thank you and very good detailed video!!!

[@ManuelGonzalez-ez5es]

I had a Cusco LSD MZ. I fixed this pulish the plate cluch but the problem continues. Does exists repair plate Cutch Kit?

[@FlatironsTuning]

Thanks for your question, yes there are repair kits or re-build kits available for the Cusco differentials. Thanks for watching and Stay Tuned!

[@gghiannabil4634]

Hallo... i have one question ...what happen when my oil for 1.5 way LSD not enught ...becouse when i drive in then stright road some time my traction tire lose and slide to left some time right way ...is that posible becouse the oil not support for prasure on the plate LSD.tq.

[@FlatironsTuning]

Thank you for your question. If there is not enough oil in the differential, typically there will be more chattering when the diff engages, and there may be more heat and accelerated wear on the clutch disks themselves. If you haven't changed the oil out, that is most likely a good starting point. Drain out the old oil, and fill the diff up with a good quality oil and see what if any difference you notice. From there, if you have a fair amount of mileage on the diff, it may then be a good idea to inspect the clutch disks if you are still having the same issue. I hope that helps and Stay Tuned!

[@jasonhugh7488]

I have a JDM STI STI type R I use as a circuit car with cusco rs in front and rear, I currently have them at 80% and front is 1 way and rear is 2 way is this correct

[@FlatironsTuning]

Thanks for your question. Basically, there isn't just one way to set these diff's up. The biggest advantage of them is that you have a ton of ability to adjust the differentials to work the way you want them to. If you are happy with your set-up, and your car works the way you want it to, then you are set. If there are any issues with how the differentials are working, you can make adjustments to improve the way they work. Hope that helps, and Stay Tuned!

[@JRICKYG]

What oil is recommended for a differential lint that?

[@FlatironsTuning]

Thanks for your question. I'd recommend the Cusco Diff oil, Motul Gear 300 LS, or Redline Lightweight Shockproof. Those are our Go-To options. Thanks for watching and Stay Tuned!

[@thespoolybois6]

He i was wondering does D25 heads on a Subaru have air injection an b25 doesn't?

[@FlatironsTuning]

Thank you for your question. Yes, none of the B25 heads had air injection. Hope that helps and Stay Tuned!

[@thespoolybois6]

@@FlatironsTuning yes that helped a lot

[@axelriet]

Changing the stacking varies the number of friction surfaces exactly as you said and ABAB is twice as much as AABB but it’s not “50% lockup” it’s 50% of the friction that you would get if you used all surfaces, which is the normal case. The terminology is very confusing and you did a great job but percentages of lockup is a terminology that was introduced by Porsche to try and make it simpler and they said 40% for the road and 75% for the track but it’s does not make any real sense other than making it easy for customers to reason about. The 1, 1.5 and 2 way terminology used in the US is another attempt at simplifying but everyone (I mean us the euro-guys who make all rally cars ;)) talk in ramp angles exclusively. Accel/Descel in degrees and preload in Newton/meter. A decent real-world tarmac diff setup on a 4x4 could be 45/60 with 40Nm at the front and 45/60 with 80Nm at the rear. You always want significantly more preload at the read for faster diff action on throttle opening, which helps the car turn, and also helps a little during tail-braking, but nothing too strong. Those numbers are pretty mild and appropriate as a starting point for a production car. For an RWD drift car something like 30/45 with 100Nm preload will lock a bit on liftoff which helps corner entry and instantly lock hard on acceleration. For a drag car you can do 20/90 with no preload and it will lock solid during launch.

[@FlatironsTuning]

Thanks for the detailed reply. There are a ton of variables when it comes to setting up a clutch-type differential for sure. More than anything, I wanted to try to communicate how many options there are when it comes to setting up a clutch type diff. Working with a shop that has a ton of experience will most likely help to get you closer with the initial set-up, but it may be necessary to adjust them to get them to work exactly the way that you want them. Thanks for watching and Stay Tuned!

[@yjudge1234]

Hi mate I’m out the process of getting LSD Cusco type rs front and mz rear 2way. Not sure if should get 1 way or 1.5 front? Car is going set up for Drag

[@4csguess19]

How do you simplify the 20/90 an so on cuz I'm having a serious noise problem wen moving slowly and turning

[@HeidiFegles]

Key words having enough power to break traction lol. I’m trying to get my center diff to actually feel good and not slip and spin the fronts. I though I had a bad clutch at first but no to much power and not enough diff to handle it lol. How to make the rears stay locked under power and not weld the center diff and ruin how well my car handles I think if I put 100 dollar bills between the clutch discs to shim them maybe I will get some performance lol 😂

[@RockJusticeVids]

11:17 he gets to pre-load and ramp-angles.

[@ImBackMan123]

The video is informative for beginners. BUT it has a lot of over simplification and could lead to bad decisions, which you want to avoid, right? I think you over glorify clutch type LSDs while underselling torque biasing ones. Torque biasing diffs (aka Torsen, Helical, etc.) do not revert to being an open diff when one wheel breaks traction. There is a set ration in which the diff can transfer power from the wheel with less traction to the wheel with good traction. This becomes less effective (as in acceleration) when there is a total loss of traction on one wheel, but it still will be far from an open diff. I got a Torque biasing lsd for my Z4 and it behaves mostly like you described: A lot of traction when accelerating out of a corner. BUT when I upset it (on purpose) it will drift (both wheels slip) properly and generate a lot of acceleration while doing so. It is definitely not behaving like it used to when the diff was open, where only one wheel was spinning and the car was loosing speed while doing so. Especially on rain it turns into a well behaved and fun drift machine. Another remark regarding your comment on how you can not setup a torque biasing diff: This is at best very over simplified. The ratios of the internal gears has a tremendous effect on how those diffs operate. Though you are right in a sense that there are more parameters and options to influence a clutch type lsd (ramp angle, number of clutch packs, preload, etc. My take on it: Get torque biasing diffs for RWD cars that you use on the street and want to track (BMW non M models) Only go for clutch type when you want absolute performance on the track or rally etc. Do not rebuild viscous type lsds, instead try to replace it with a clutch type (BMW E46 M3, E92 M3, etc.)

[@Iseenoobpeoples]

This video is wrong, the wheel speed difference from side to side has nothing to do with the locking action. The engine torque is transferred to the pressure rings, the cross shafts are resisting this force since they are connected to the wheels. The two opposing forces (driving torque vs loading torque) is the reason why the cams are sliding into the locking slopes.

[@douglasweaver6783]

I'm very interested to hear the response to this comment. The only part of the how the diff works that I did not understand is what causes the cam to move/apply force.

[@JamesLivas]

Thank you, I came looking for a comment like this. If it was purely wheel speed difference then doing circles in the parking lot would lock the diff solid. Locking would be directly proportional to steering angle, and this is not the case.

[@bv2010]

One unintelligent embarrassment disliked this video.

[@FlatironsTuning]

Thanks for the comment. It's all good. Thanks for watching and Stay Tuned!