How does an LSD work then?

[schueymcfee]

Had a big bang from the rear last month and lost all drive.

Finally got around to having a look and its a broken half shaft rather than a knackered diff.

But my understanding of LSDs was that even with one side broken the other side should still drive the car.

I lifted the car up onto jacks and started it up - the side that was okay the wheel spun round, but you could get hold of it and stop it.

I thought this couldn't happen?

[Phil Durn]

My understanding is the same as yours, there should be some slippage between wheels otherwise you couldn't turn. I suspect that your the LS part of your LSD is knack'd, sorry, not working.

[victormeldrew]

In my experience they work rather well, you just pop them in your gob and swallow. Er, oh, not that sort of LSD. Sorry.

It does sound like you have a USD there - unlimited slip diff. Maybe thats why the half shaft broke, it was doing all the work. Just a thought.

>> Edited by victormeldrew on Sunday 30th October 21:44

[tahiti450]

schueymcfee said:

But my understanding of LSDs was that even with one side broken the other side should still drive the car. I lifted the car up onto jacks and started it up - the side that was okay the wheel spun round, but you could get hold of it and stop it. I thought this couldn't happen?

This is not inconsistent with an LSD. Bear in mind that the degree of locking is proportional to the amount of torque being applied. So in operation the more power you put through the input shaft the harder the clutches inside the diff bite and progressively lock the output shafts to eachother (in effect).So on the stands with the engine idling and the wheels off the ground , there is virtually no resistance to the wheel turning so almost no torque being applied (only that needed to overcome internal friction in the diff and rear hubs), so if the LSD is working properly there should be little limited slip effect. tryinhg to drive the car with a broken halfshaft is like having one wheel off the ground- so no resistance to rotation on that side so no torque reaction and little if any locking up of the diff.
Stopping the spinning wheel should just make the other output shaft double its speed, like on a normal diff. Depending on the type of limited slip mechanism and the amount of wear / mileage on the diff there may be some pre-load or residual stiffness / drag in no load conditions (the Jag' Salisbury diff on my XJS is quite stiff if you try turning one raised wheel with the other fixed or on the ground). Your diff would have to have a massive amount of preload to be able to make the car move as above, i think I'd be more worried if it did!
Incidentally which diff have you got GKN, BTR or even Hydratrak! ?
PS see p231 in the Bible.

>> Edited by tahiti450 on Sunday 30th October 22:22

[schueymcfee]

That sounds like good news then!

Mine is the earlier GKN.

Thanks for the info.