LSD Clutch Test

#1

Does anyone know what good numbers are for the torque wrench test? I want to know if my clutches are worn out in my diff. I have no idea how many miles my diff has on it or the condition of the clutches. I had a friend drive my car at an event this year and he felt the diff clutches were worn out. I was on the fence and felt the curb paint was just slippery.

To help evaluate I did the standard test (or only test I know) starting with a cold car. Jack up one rear wheel. Put car in neutral. Put torque wrench on axle nut and keep increasing torque until it breaks free. Mine broke free at 53 ft lbs. I don’t think that’s all that bad but not sure how much more hold fresh clutch disks would have. If there is no need for a rebuild that’s one less thing on my list this winter.

Anyone know what good numbers should be? I know this is somewhat relative due to differences in torque wrenches but I am looking for a ball park.

Thanks,
Jason

#2

Anything above 50ft-lb is good. The highest observed for a freshly rebuilt diff would be around 65ft-lb, as I recall.

#3

mahoneyj wrote:

[quote]Anyone know what good numbers should be? I know this is somewhat relative due to differences in torque wrenches but I am looking for a ball park.
[/quote]
There’s some good old threads on this. Yours is a lot better than mine, and I’m not spinning a wheel at turn exit. Car, sometimes. Wheel, no.

#4

Mine was also 53 ft/lb.

#5

Thanks for the info guys. I will remove the diff rebuild from the To Do list this year.

Thanks,
Jason

#6

Does the break away reading go up or down when the diff is hot?
Anyone test it before and after?

#7

[quote=“jlucas” post=58068]Does the break away reading go up or down when the diff is hot?
Anyone test it before and after?[/quote]
I tested it hot and cold and didn’t find a difference worth mentioning. The accuracy of a torque wrench is, what +/- 5%, and the difference was 1 ftlb.

I was in an interesting discussion a couple months ago about the ideal LSD set up. One extremely experienced person said that the ideal LSD is just strong enough to prevent the rear wheel from slipping, but no stronger than that. If, so his arguement went, the diff is stronger than it needs to be, it causes understeer at turn-in because the diff doesn’t want to “break”.

Not everyone in the discussion bought this theory but to me it makes a lot of sense. My diff breaks at ~45ft lbs and my rear wheels don’t spin in turn exits that I know of. My worn diff might well be better then your cherry diff .

#8

I had the same problem coming out of 10b @ RA coming up the hill. I rebilu mine about 4 events ago and I was the random car through tech at the NASA June Jam. When Patton checked my diff it was EXACTLY 65ftlbs. Now the problem is me going around RA and not the diff. lol