Testing LSD out of car

[Earendil]

First off, I've found plenty of info for testing the LSD and the break away torque for when the LSD is in the car. 55 ft/lbs is the most often quoted number. But I'm not here about the number and how to test it while it's in the car.

What I'm wondering is if the LSD can only be effectively tested when it has the pressure of the axles against the output flange?

I ask because I have a 4.10 LSD in my possession that I bought from a guy here on R3V (nameless for now). He seems the honest sort, and when I picked up the diff we had a friendly 45 minute discussion about E30s :)

Anyway, it was obvious the LSD was an LSD, but it also seemed to slip easily. The seller claimed this was because the oil had drained away from the clutch having sat for over a year, and that the oil was probably nasty old.

I drained the oil, added Redline 75w90, and started turning the output flange by hand (by which I mean using a pipe). It started to stiffen up, but I could still break it loose just using my hands (and I'm not on the stronger end of the male spectrum). However, and the reason I ask, is that I can not break it loose with my hands if I apply some pressure on the output flange. Is this a fluke? Did I buy a junk LSD that can't hold shit?

[jlevie]

The torque test is valid whether the differential is in the car or not. Hold or rig up a lock for one output flange and bolt a plate with a nut welded to it to the other flange and test with a torque wrench. Before doing that spin the input shaft a number of times to coat the internals with lube.

[shiboujin]

With a diff out of the car and nothing bolted together, you should be able to hold one axle stub and spin the other axle stub freely. Rig up something to hold the output shaft and one axle stub, then hook up a torque wrench to the free axle and THAT is your break away torque figure.

[Earendil]

With a diff out of the car and nothing bolted together, you should be able to hold one axle stub and spin the other axle stub freely. Rig up something to hold the output shaft and one axle stub, then hook up a torque wrench to the free axle and THAT is your break away torque figure.

Could you clarify that? I'm thinking that an "Axle stub" should be the same spinning assembly as the "output shaft". Do you mean input/drive shaft?

[shiboujin]

Um yea I mean input shaft not output shaft.

Make device that:
Holds input shaft
Holds 1 axle stub

Take torque wrench and rig it to the non bolted down axle stub. Where the stub starts to move is your break away torque.

Now, remember, this has nothing to do with lock up %.

[Earendil]

Um yea I mean input shaft not output shaft.

Make device that:
Holds input shaft
Holds 1 axle stub

Take torque wrench and rig it to the non bolted down axle stub. Where the stub starts to move is your break away torque.

Now, remember, this has nothing to do with lock up %.

Got it!

I was concerned because my 3.73 turned in step without touching the input shaft, but this 4.10 could easily be turned in opposite direction by hand. I'll try locking down the input shaft and see if that changes things. Thanks!

[shiboujin]

An LSD will act open under the circumstances you mentioned. The real way to test the health of your LSD is to test its break away torque.

Maybe take a look at my write up on LSDs. http://e30performance.info/viewtopic.php?f=22&t=1311

[Wanganstyle]

Anyway, it was obvious the LSD was an LSD, but it also seemed to slip easily. The seller claimed this was because the oil had drained away from the clutch having sat for over a year, and that the oil was probably nasty old.

Oil no oil, the item will still lock. LSD units completely dry will lock simply based on the fact that the LSD center unit has springs inside that make sure there is pressure on both sides. IF your LSD unit is destroyed, worn out, then this could be possible.

fresh rebuilt units with 0 oil still spin and lock...

you need to fix one output axel flange and add torque to the other one to see if it locks - otherwise you cannot check.

LSD internals in the cartridge can wear so severly that an LSD = open. I have done this with carnage to my prior E36M oem LSD, it was useless.

also, you should remove the back plate and look at the center to make sure its a LSD, looks like a big cylinder - NEVER trust sellers or plate tags for this...

also, the LSD cartridge has 8x 6mm allen bolts that often back out or get damaged causing serious issues- you should check these and add lock tite if you really care about your car :)