How do I test an LSD?

[Lee]

Dealing with Jeeps for most of my life and I have installed lockers of various styles. None of them would be damaged by Mot brake tests or rolling roads.

If you do remove the LSD or ring carrier and change bearings you just need to make sure the backlash is correct after installation. A magnetic base and dial gauge make this easy. I am not sure if the BMW cases are adjusted with shims or adjustable preload nuts.

I have built a lot of diffs and as long as you understand the settings and have access to the tools they are not difficult.
Anyone can find alot of information from Randys ring and pinion, A US company that specializes in different diffs.

Reading it all makes it look complicated but there is a lot of very good information that can be transferred to any rear end.
https://www.randysworldwide.com/resource-center/?fwp_resource_center_categories=gears

Beat me to it, I was going to say just this.

The Z3 diff preload is done with that crush washer, easy to do with the torque angle gauge 25nm of load if my memory serves me well. The LSD unit is done with shims either side you'll need some engineers blue to know that the teeth are meshing central. That first video you listed is the guide I followed.

 

[Delk]

I dealt with Randys for years with off road stuff and their assistance and service is excellent. They dont do BMW gear sets as far as I know but the basic principles are the same.

The only downside to crush sleeves on the pinon is they are one time use. With shimmed pinions you can change seals and items without needing to replace anything else.

 

[Brian H]

Love this place, everyday a school day

 

[Dino D]

Love this place, everyday a school day

Sounds very serious and proper engineering like, I’ll best stay out of it in case I lose a limb or something

So for Health and safety reasons I’m going with TIFF’s technique to test a a diff:

View: https://youtu.be/Vocpe0eZUWg

 

[t-tony]

Last one I did was in a Transit, not the type where you could pull the Diff. out of the axle. This was the twin wheel rear axle and you had to build the Diff. (including shimming it) in the axle casing on the vehicle. A right PITA to be honest.

Tony.

 

[motco]

Chaps, I had quite forgotten that I had consulted the manufacturers on this matter two years ago and their advice was to play safe. Here is the text of the reply:

The Torsen differential is similar to other types of LSD in that it generates internal friction in order to resist wheel spin. The reason that the “safe” test exists is that if the dyno forced differentiation at load conditions that the LSD normally prevents. Doing this can burn up the friction surfaces, usually clutch plates.


However, the Torsen does not use clutch plates, and the amount to friction that its gearing creates is proportional to the amount of drive torque is applied to it. This allows the Torsen design a little more flexibility under these conditions. So, if the test applies a load with a roller to the tire, while the other tire is free to spin the opposite direction, it should not cause too much concern. This assume, however, that the torque it applies is relatively low, with a differential rate less than, maybe 100 RPM difference from side to side, and the other tire provides no resistance to differentiation. This is somewhat comparable to making use of mini-spare tire, which Torsen allows but most LSDs do not.


However, if you have any concern about the test being more severe than described, I would suggest defaulting to the “safe” test. The Torsen-type design allows greater tolerance of these types of situations, but there are limits to it.

There is no doubt in my mind that there is a risk of damage to the diff by testing on the brake rollers because there is an artificail situation wherein the driven wheel rotates infinitely faster than the opposite wheel because the non-driven wheel is held stationary whilst its opposite number is being tested.

 

[DiffManDave]

Don't know much about LSDs. Currently scrubbing one up to put back on my rear end refresh.

Found this article which sounds quite informed. Could anyone comment if the advice & checks are reasonable. Anything else I can do?

https://e28goodies.com/buying-a-lsd-you-better-read-this/

It makes a bit of a grouching noise on one side. It sounds the same as debris caught between a brake disc and splash-guard. So I'm hoping it's just a dislodged rust flake. Otherwise I might have to look at replacing a bearing.

Started having a look at procedures. This is a good one on youtube.

View: https://www.youtube.com/watch?v=qeMIh9mGwRY

It sounds like there is rust behind the dust cover. You can just tap them off with a screwdriver and replace them. They are still available from BMW approximately £15 each last time I bought some

 

[mrscalex]

I contacted @DiffManDave via his listing on eBay for rebuilding BMW LSDs. And he joined up after asking about the forum.

Dave, feel free to create a post advising of your services. I think people will welcome that as it’s a bit of a gap in collective knowledge on the forum though you’ll see a determination here to catch up.

 

[DiffManDave]

I contacted @DiffManDave via his listing on eBay for rebuilding BMW LSDs. And he joined up after asking about the forum.

Dave, feel free to create a post advising of your services. I think people will welcome that as it’s a bit of a gap in collective knowledge on the forum though you’ll see a determination here to catch up.

Thanks mrscalex.

So I run a company called Heasman Differentials, I specialise in building / modifying and setting up BMW differentials for both road cars and race cars.
I can setup your lsd for your particular driving style, race track and also correct handling problems providing you have an adjustable LSD such as Gripper, Drexler etc.

I am also a dealer for Quaife, Gripper and Wavetrac.

www.heasmandifferentials.co.uk

 

[the Nefyn cat]

Thanks mrscalex.

So I run a company called Heasman Differentials, I specialise in building / modifying and setting up BMW differentials for both road cars and race cars.
I can setup your lsd for your particular driving style, race track and also correct handling problems providing you have an adjustable LSD such as Gripper, Drexler etc.

I am also a dealer for Quaife, Gripper and Wavetrac.

www.heasmandifferentials.co.uk

So, stupid question number one, being as my Z3 has a Torsen diff, do I need to use an "LSD" diff oil, or is it alright with a normal diff oil? Not the sort of thing I change that often, but I've often wondered.

 

[DiffManDave]

So, stupid question number one, being as my Z3 has a Torsen diff, do I need to use an "LSD" diff oil, or is it alright with a normal diff oil? Not the sort of thing I change that often, but I've often wondered.

Normal diff oil because it’s only gears inside. A plated diff needs the thicker LSD oil because it has moly coated clutch plates inside that would wear out very quickly with normal viscosity diff oil.
Plated diffs also need regular oil changes because the moly coating wears off the plates , contaminating the oil and getting into the bearings causing premature bearing failure

 

[the Nefyn cat]

That's what I was thinking, nice to have it confirmed by someone that knows about these things.

 

[DiffManDave]

That's what I was thinking, nice to have it confirmed by someone that knows about these things.

No problemo

 

[mrscalex]

Normal diff oil because it’s only gears inside. A plated diff needs the thicker LSD oil because it has moly coated clutch plates inside that would wear out very quickly with normal viscosity diff oil.
Plated diffs also need regular oil changes because the moly coating wears off the plates , contaminating the oil and getting into the bearings causing premature bearing failure

Thank you. So what product for the Torsen would you consider a) good, b) better & c) best?

 

[DiffManDave]

Thank you. So what product for the Torsen would you consider a) good, b) better & c) best?

Coming from a BMW background, I only use Castrol.
Syntrax 75-90 for torsen, 75-140 for plated. You can’t go wrong

 

[mrscalex]

Coming from a BMW background, I only use Castrol.
Syntrax 75-90 for torsen, 75-140 for plated. You can’t go wrong

Nice and straight-forward Thank you

 

[motco]

I had a 1985 Capri 2.8i Special as a company car once. Soon after I got it I noticed a sound like distant barking dogs whenever I made a tight turn in a quiet environment such as an underground car park. As it was silent when running straight ahead I assumed it was the LSD - which my earlier 2.8i (1983) did not have - making the noise. Thus it proved to be and it was changed under warranty. I used to drive 50k miles per annum so 'a short time' could have been 30 - 40k I suppose.

 

[DiffManDave]

I had a 1985 Capri 2.8i Special as a company car once. Soon after I got it I noticed a sound like distant barking dogs whenever I made a tight turn in a quiet environment such as an underground car park. As it was silent when running straight ahead I assumed it was the LSD - which my earlier 2.8i (1983) did not have - making the noise. Thus it proved to be and it was changed under warranty. I used to drive 50k miles per annum so 'a short time' could have been 30 - 40k I suppose.

That’s the sound of the friction plates rubbing against each other. Nothing wrong with it, just a noise.
I liken it to dragging a chair across a floor, sometimes it makes a noise, sometimes it glides smoothly.
It’s fixed easily with an oil supplement called Friction Modifier which allows the plates to slip smoothly rather than “slip, stick,slip,stick”

 

[Nodzed]

Normal diff oil because it’s only gears inside. A plated diff needs the thicker LSD oil because it has moly coated clutch plates inside that would wear out very quickly with normal viscosity diff oil.
Plated diffs also need regular oil changes because the moly coating wears off the plates , contaminating the oil and getting into the bearings causing premature bearing failure

Good to know luckily I have done my M diff twice now in 50k, think I'll do it again over the winter

 

[Nodzed]

No issues roller testing LSD equipped cars at roller speed.

Tony.

Are we sure about this? would really like a definite answer not that I don't trust your experience Tony its just the M diff is not Torsen @DiffManDave can you advise?