Beantown Kman

The way you drive? Yes! What are you going to do about it?

Bill Lehman

I'm considering a Guard, It was one of the best mods I did to my 987. I'm thinking that if my 3rd gear was going to fail, it would have by now.

James88

l'm guessing this with gear in neutral, yes ?
Edit; just found the answer, yes in neutral.

bhk1004

If there is no preload won't it freely move regardless? I don't fully understand the mechanics so definitely just asking to know. Just from what gtgears posted saying no preload on the gt4. Maybe it loads when 1 tire spins?

chillindrdude

I am not sure what the break-free torque specs on the GT4 lsd. But with the one rear wheel on the ground, if you try to rotate other rear wheel that is in the air, it should be hard to rotate. If it is easy to rotate, then your lsd is worn.

GTgears

It is zero, as I stated earlier in the thread. Theres no resistance and if both in the air it will spin opposite like an open diff.

chillindrdude

Forgive me, I missed the comment.

But I'm alittle confused. Correct my misunderstanding, I thought the definition of a LSD, is that with no load, its like a locked/closed diff. Once a certain "breakaway" torque is reached, it opens. If the breakaway is 0nm, it's essentially an open diff right?

GTgears

You are mixing preload with the actual locking of the LSD. When the LSD activates, the pins the spider gears ride on push against the ramping on the pressure rings. The pressure rings put force on the clutches, locking it. How much is locks, which Porsche expresses as a percentage, is dictated largely by the angle on the ramps.

With a zero preload LSD, it does behave as open when there's no wheel slip. There's no belleville washers to clamp the clutch pack in normal use, and if you go around a corner, there will be no load on the clutches. But if you went around a corner and gassed it hard, making the inside wheel spin, it would still kick the spider gears into play moving the pin up the ramps and locking it.

The stock GT4 LSD is deliberately very anemic. 22% on throttle, IIRC. What that means is if your inside wheel is free spinning, no more than 22% of power can be transferred to the outside wheel. Porsche has never produced a full 100% locking LSD except the braking side on the 930/964T models.

I'm sorry I wasn't ever able to post my Cayman LSD article. It's still on Planet9 but due to photobucket's new pay policy the pictures are gone. Since I have changed computers over the years I no longer have original photos I can upload and post.

James88

Thanks for the explanation GTgears.
So there's no simple way of testing the GT4 LSD to work out if its worn, is that correct?