vette951s

I'm trying to rebuild the limited slip in my Turbo Cup car; however my local P-car dealer parts guy says the only part listed for the inner disk is for a standard 944 turbo or part #951.332.551.00. This inner disk is only 2.0mm thick, not 2.5mm as installed in the Cup/AOR transmissions. The parts guy said he looked through all current PETs and Motorsports catalog with no luck. Does anyone know the correct part number?
On another note, does anyone know of a way or the parts necessary to increase the 40% limited slip standard ratio to something higher like 80% that the 911 boys appear to be able to do?



Thanks, John

Van

I'd like to know the answer as well... I would like to increase my lock-up, too.

gt37vgt

take 2 or three to a toolmaker have them carefully ground down to 1.3 ,1.2 ,1.3, and hardness checked.
also be aware a 911 is a completely different animal that benefits from asymmetrical load ramps and a 944 doesn't. Also go for a lock ratio according to the tracks go do the high lock for mid speed stuff is not so good for the realy high speed stuff.
And while we're here can anyone tell me the break out torque between the 2 axles for a given slip % ratio ???
other wise we are all fumbling in the dark

Van

The factory manual says that the Turbo S (40% locking) should pass a torque wrench test between 10 and 35 Nm (large range there...)

That's 7.3 to 25.8 ft. lbs.

Oddjob

The last time I looked into replacing/rebuilding LSD internals, the only parts that are still available from Porsche are the AOR guts. For anyone with a pre Turbo S LSD (-03 version), all the parts supercede to the AOR parts so you have to buy the Turbo S discs (which are thicker than the non-S LSD discs) and pressure cups/rings (which are machined to accomodate the thicker friction discs).

If the -04 Cup LSD uses dimensionally similar discs and pressure cups as the AOR (-05) LSD, then you should be able to get the replacement discs from a dealer. I dont have access to my part number info at home, but will track down the correct PN's at work next week.

I do know that lock rates can be changed by machining the ramp angles on the pressure cups. I have also heard of a shop that uses 930 LSD friction discs (and/or other components) in the 944 LSDs to increase lock, but I have no first hand experience with trying that. Be wary of recommendations of packing additional or thicker discs into this type of LSD, as this can possibly cause excessive friction/heat and premature wear and failure of the units.

George D

PM me if you want to talk with someone that does this fairly often. They can be adjusted.

Oddjob

951 332 551 00 is the thicker Turbo S/AOR disc. The earlier part# (for the regular 951 -03 LSD) is 917 332 551 00, which is no longer available.

boost feen

Just throw that cup car transaxle away for once John!

Bill

John,

Another good source for information and possibly parts would be Paul Guard from Guard Transmitions. He manufactures most of the motorsports diffs for Porsche. He makes the best diff for our cars, bar none. I have spoken with him, he is a great guy and very helpfull.

vette951s

OK, here is my book report on this subject.
First of all, many thanks to Mike at Guard Transmissions. Helpful does not even begin to describe his contribution to my education on Porsche LSDs.
After much research and communication with many people on the subject, it appears that Porsche indeed superceeded the part #951.332.551.00 to the later turbo S style 2.5mm thick friction disk, although I did not buy the friction disk from the dealer and measure it myself. Given this, I don't know what non turbo S transmission people will do when they rebuild their LSD as these will not fit! Guard Transmission may have some custom thinner external spline disks and cone washers to make up some of the difference, but .....? My problem was that although all my components measured up to be within factory tolerances, my breakaway torque still would not go beyond 17 ft lbs., or about halfway in the factory spec range. After many phone calls to Mike at GT and remeasuring and fitting, I ended up sending my unit to him. He indicated that although still appearing good, my friction disks were a little worn and since Porsche does not use the best material for the job, some GT disks were purchased. Also, my cone washers were weak (although still measuring 2.0mm), so some custom 2.2mm cone washers from GT were acquired to increase my breakaway torque. I just got everthing back a couple days ago and have not yet fit the new components.
Regarding increasing the lock up ratios, our LSD pressure ring ramps are designed with a 40/40% acceleration/braking ratio. The components wear somewhat quickly and become more slip than limited in short order. The only way to increase the 40/40 ratio, absent purchasing a new LSD unit with different ramps, would be to double the friction disks. However, there is no room for this using available factory components. Machining the pressure rings is out as this would remove the hardened surface. Similarly, the external splined disks need to be perfectly flat and hardened. GT is working on this and may in the near future have custom components available to achieve a higher ratio. However, doubling the friction disks may lead to a 80/80 ratio which may be too much for a front engined car - opinions?

John
Rothman Turbo Cup
'91 951S Cabriolet Clone
'92 968TRS Clone

nize

i think that 80/80 would indeed be too much. i'd be interested in a 60/60 or a 50/50 though.

boost feen

So I realize that the 968 G50 based transaxle weighs a few pounds more but why wouldnt one want to take advantage of the much more plentifull gear options available as well as the many different clutch and springs available to custom make any limited slip variables under power and on overrun. Take the 968 turbo S limited slip at 75% / 75% and I believe the turbo RS was a higher ramp. I would imagine its cheaper to build these trannys up and since they are heavier duty they can handle more abuse, lets not forget that having six gears is far more competitive in the vintage 951 or in some peoples case just plain faster times which is what were after here right!

333pg333

Then there's the school of thought that the 931 is the strongest of the lot...
http://www.porschehybrids.com/gallery/album22
Oh, and I have a Motorsport 80% lsd and I'm not sure of what the proclaimed downside is meant to be? Too much understeer, no. Too much lock on backoff, no. Fit straight into a 951 box, yes...

thingo

I've had a fresh 951 LSD, a 'shimmed' 968 LSD, and a 80/80 968 LSD, the shimmed 968 was better than the 951, but the 80/80 is better again,you notice it a little on the street,but it is not a problem, it is just better on the track, the car is more stable.

Airflite40

I have also read that before, but its only the G31 snail shell trans

edit: thanks for that link, lots of great info in there.