kary993

Well, I knew the day would occur when the LSD would completely give way, but yesterday during the timed run session at the California Speedway, my LSD was completely slipping in the decreasing radius right hand hairpin (turn 9). There are some bumps in there as well making it worse. Since I have not driven the car without LSD I am not entirely sure what it feels like. The feeling I was getting was the car was going no where when I pushed on the throttle. I thought I heard some spinning but nothing was happening. I thought at first I had mis-shifted from fourth to fourth (duh) but found that I was in second but had to lift off the throttle and then slowly get back on it. As a result I have been slowly over heating the right rear tire causing a delaminating of the tire (not good at 140mph on the left hand banking since it is the outside rear tire!). This situation (tire failure) happened at the Speedway a few months ago which I attributed to too much camber in the rear. I subsequently reduced the camber by 1.5 degree to help with the banking situation. Now with less camber I still had a tire failure but now the limited slip is really slipping. I did not experience this LSD feeling a few months ago.

So my question is this, what does no LSD feels like or a failed LSD feel like?

Also, do you think this is why the tire over heated because of the slipping or because of the camber on the banking or both?

I'll post over on the race forum as well....

TrackJunke

You described exactly what it should feel like.

chris walrod

A worn LSD will also be noticeable on the brakes as well, typically the most obvious as Porsche used 25/65 ramps, 65% lock being on the decel side. Have you noticed the any more twichty or nervous while decelerating?

Was the track layout the typical one used for CFoS? IIRC, there were only 3 or so right-hand turns, other than the medium speed chicanes.

If you had clutch slippage, you sure would have smelled it. Very well could be the the diff clutch plates have given up the ghost.

There has been more than a few reported gearbox problems caused by pitting spider gears coming apart. You may want to at least drain the oil into a CLEAN pan, then filter it with a paper paint filter and see what you had in the oil...

Let me know if you need help!!

kary993

Chris,

I did notice some twichy movement coming down from 145 mph to 50 mph turning into the infield. Likely could be another sign. I did not notice any clutch smell at all. I just put in the new lightweight flywheel/clutch in January.

The engine was running very cool but could the tranny/differential possible gotten too hot now that I could run the engine so hard?

chris walrod

Kary, I could never get to even 135mph on exit of the oval turn two, right before the braking zone.....not enough cajones in my case. 145mph is awesome! That is a fun track layout, I must admit.

Anyhow, just sent you a PM..

kary993

Chris, that was my fastest, usually around 137 to 142. The good thing about a wing is the stablility, the bad thing is the drag!

Greg Fishman

Unless you run a 993's tranny for over an hour or more on the track you will not get it near hot enough to cause the fluid to break down.

Just did a search (novel concept!) and here are a couple good threads with info from the head guru himself.

https://rennlist.com/forums/showthre...+differentials

https://rennlist.com/forums/showthre...+differentials

kary993

Greg, thanks for the search however I already understand how they work. Maybe I missed something in those threads but I did not see the answer to my questions there.

Greg Fishman

"So my question is this, what does no LSD feels like or a failed LSD feel like?"

While I think it would be hard to tell someone exactly what it would feel like, I figured the best way to know if it was working or not would be to test it. I think Steve gave some good advice about that.

My experience in a car that had no LSD (not a worn out one) was that the inside tire would spin in low gear, slower turns. It was pretty obvious as you could hear the tire spining and from the amount of smoke coming from the rear of the car, if you got on the gas way too early. If you were getting a lot of wheel spin then that certainly could explain the overheating and failure of the right rear tire.

kary993

Thanks Greg. It was particularly surprising to me to have lost the LSD during the session in such a big way. I had been having issues with it on bumpy surfaces since I changed my suspension out so I just thought it was the stiffness of the new suspension causing the slippage. It would always catch rather quickly even over multiple bumps. Kind of like a catch, slip, catch, slip, catch sequence. So in this situation it completely went away and in the heat of competition timing I was perplexed as to what was actually happening.

That is why I was asking how it might have felt without LSD or with a failed one. I appreciate the feedback as it confirms my thoughts. BTW, I did jack up the rear end and try spinning the wheels, nothing happened on the opposite side; however, I recall someone, I thought it was Steve, mentioning that that test is not always accurate. ??? Not that I care to try and save this LSD as I do think it really is shot and I would like to get a motorsport clutch based LSD.

Anyone happen to have the part numbers handy for the Porsche motorsport clutch type LSD? I do not want to get in trouble with Pheobe!

viperbob

Why not go with the Guard LSD?

kary993

Well, Bob, that is a good question. Which one is best? Is the Guard clutch type LSD as good at the Porsche Motorsport version?

Coleman

The guards has a billet machined body and the P_Motorsport one is cast... the Gaurds will set you back 2K though....

Coleman...

Steve Weiner-Rennsport Systems

You get what you pay for,.....

The Guard LSD's have a 4340 chrome-moly case and you NOT break those,...

I've seen enough Motorsport LSD cases snap on the ring gear side that I recommend the GT ones, hands down. Guard LSD's come set at 80% so you might want to restack the plates to 40% for less understeer at low speed. Its a personal preference thing.

clubsport1

A couple of months ago I had to replace the clutch plates in my lsd. The mechanic contacted Porsche motorsport to get the replacement M/sport parts.
Unfortunately they no longer had the G50 versions on the shelf and provided GT3/RS plates instead which somehow were the equivalent of $300 cheaper.
The lsd works fine now on road and track...I am led to beleive once you go down the motorsport route, the lsd is more or less good for the life of the car.