Have a 87 LSD that I think needs rebuilding. How many ft lbs of torque before breakaway? Anyone have any old disks after rebuild? Want to experiment. I only have 15 ft. lbs before it slips.

Thanks, evlu

 

The 89-91 US models that came with a LSD (the 89-90 GTUs (note the small "s"- don't confuse with a GTU)) and the 89-91 Turbo used a viscous LSD that never wears out.

So the only way you would rebuild a LSD from one of those two models that came with it, would be to replace it.

and how did you measure that it lets go at 15 ft lbs? You do know that viscous LSDs need about a revolution or two of separation to lock?

 

Sorry, mis-typed. It's an 87 non-turbo with discs. measured breakaway with torque wrench and fixture.

evlu

 

That is completely wrong, a viscous LSD does "wear out". The special fluid inside breaks down over time and becomes less and less effective to the point that it ceases to limit slip at all. Sure there's no parts that wear, but it still stops working as an LSD, so yes, they do "wear out".

 

Yeah, I keep hearing people say that, yet every single one that has had regular gear oil changes that I have seen with 200K miles + on them work just as fine as they do when new. Maybe you have to have 300K miles on them to wear out? Either that or overheat it by never changing the gear oil.

I suspect that people that claim they wear out just don't know how to test a VLSD as they don't lock up like a clutch plate or Torsen based LSD will.

Now burnt out because the owners suck forgot to do regular maintenance and overheated the rear end... well I guess someone would call that wearing out. But that really wouldn't be worn out... it would be burnt up.

 

I know in the miata community it's widely reported that after maybe 70k miles the diff's ceased to be useful in limiting slip, even when it's not been abused. In an SCC article about their 350Z project car they noted how the VLSD was behaving very badly and not locking up as it's supposed to (it had been abused though).

Now what to call it is sammantics, but the point is that it's not guaranteed to still be working just because it "can't wear out". The diff fluid that's replacable isn't the working fluid for the limited slip that breaks down over time, and old fluid has nothing to do with overheating the inner workings, you could do that with new fluid equally easily.

My open diff only once gave me one wheel spin, and that's when the front swaybar came undone from one endlink. I don't know what you mean by they still worked fine, but unless you tested it, there's no good way to judge if it's still ok or not.