LSD question

dfink · 05-10-2007, 06:44 AM

In searching I think I already know the answer but am looking for opinions anyway. I seem to not be able to put the power down at auto-x anymore. I get alot of wheel spin coming out of corners hard that I didn't used to get but I did re-do the suspension so that could be a factor. I used to have horrible under-steer and since the suspension now have horrible oversteer.
Anyhow when I rebuilt my tranny I was suprised to find it had an LSD unit. If I jack up the rear end, take car out of gear and turn the wheels they go the same direction. If I put the car in gear and turn they go the oposite direction. It does not take much to turn the wheels with the car in gear.
I have not done the burn out test but do get considerable wheel hop when launching hard at auto-x. Car has 80,000 miles on it and I doubt the LSD would have been serviced.
Is the ease I can turn the rear wheels the indication that the clutches in the LSD have long gone south.
In reading it didn't look like they should lock up until torque is applied and a plate pushes on the clutch pack. But there should still be some preload to the clutches. I did not remove the LSD when I rebuilt the tranny last year.
I am not quite sure on the test procedure I seem to find conflicting methods. When testing out of the car at the flanges is the tranny is gear or open. The on car test says to put gear in first do not block wheel then test torque. The in car method has one flange blocked but did not say where it is in gear.
It seems you should have it in gear and one wheel blocked to emulate the in car test. I hate to pull the LSD only to find it was OK. I also would like to have it working.

dfink · 05-10-2007, 07:08 AM

A little more info.
It takes 25 ft lbs one direction
It takes 15 ft lbs the other direction
Tranny does have the 12 designation

Perhaps on an old tranny 25 is not so bad.

Bill Verburg · Bill Verburg's Garage

Your lsd stock was a 40%, but w/ reduced # of friction surfaces form previous 40% lsd's.

They are prone to quickly wearing out and even when fully functional aren't the best from a performance perspective.

In any event if A/X is your thing a Quaife gear type is preferred because it doesn't induce the trailing throttle understeer that the clutch type do.

dfink · 05-11-2007, 05:17 PM

So where does one find parts for the LSD I can't seem to find them anywhere. Probably not gonna spend $1700 on a quiafe.

Tom Oxner · 05-11-2007, 05:54 PM

Have you tried Gary Fairbanks 1(203) 866-2466? He is a good guy and really knows Porsche transmissions.

Tom Oxner