coilbox

Got myself a stock LSD gearbox, the car reads 150.000miles. Got time to open and inspect it, before installing it on my car.

Any way to test de LSD for wear?

Any source of the friction plates if needed?

Thanks!

Ben951S

Try searching here and on pelican. I *believe* some one did a full teardown with great pics... probably covers some of your questions! IIRC some special tools/presses needed, but if you have time, can bring it piecemeal to a place to press.

rlets

I'm in exactly the same boat. I'm thinking about just hiring the LSD rebuilt and the 5th gear swapped instead of sciencing it all out myself.

Here's the rebuild thread Ben951S mentions:
https://rennlist.com/forums/996-gt2-...d-rebuild.html

Rich

Richgreenster

How much does this cost?

Droops83

With that kind of mileage, it is guaranteed to need a rebuild. The factory manual shows a procedure for checking breakaway torque with the diff removed from the transmission, but the spec is pretty wimpy, and breakaway torque is not the most accurate means of gauging wear (when you first rebuild the diff, the breakaway torque will be higher than it will be after a few track weekends, etc). Rebuilding will make a big difference.

Matt at Guard Transmission has everything you need to rebuild your LSD. Note that removing the 944 diff is more involved than the GT3 diff referenced in the link above. The 944/951 trans is facing the opposite way that the transmission in the rear engined 911 does, so the input shaft blocks the ring gear on the differential. Simply removing the side cover with the trans in the car is not possible as in 911s The transmission needs to be removed from the car and the shifter assembly, tail housing and gear cluster need to be pulled in order to remove the diff. If the carrier bearings need replacement like mine did, this makes it a pain as you will need to remove/reinstall the gear cluster several times when checking bearing preload/ring gear backlash. Also, the 944/951 diff comes apart a bit differently, in that there is a cap on top of the diff housing that comes off; you do not have to remove the large ring gear bolts to disassemble as you do with a 911 diff. Once apart, it looks similar to the GT3 unit in the pics except there are only 2 plates per side instead of 4. Guard can set yours up as a 4 plate if desired, provided there is enough clearance.

TonyG

If the transaxle is on the bench, I can get the diff out in less than 5 min.

The shimming is done on the pinion bearing race back side. You don't need to R&R the gear stack. You seperate the gear box from the transaxle housing, and adjust the shims on the back side of the pinion bearing race, then bolt the gear housing to the transaxle case and recheck the R&P mesh.
TonyG

Oddjob

What model/year LSD?

The discs for the early LSDs are no longer available from porsche. They have been replaced w/ the Turbo S/AOR discs, which are thicker. Problem is that you also need to use the Turbo S/AOR pressure cups. So its about a $400-500 upgrade just in factory parts to rebuild a non-S LSD.

Other option, as mentioned above, is to contact Matt at Guard. He can rebuild the early LSD using Guard discs. But this is not going to be any cheaper to have done.

The break away or slip torque test shown in the manual does not really give a direct indication of the condition of the friction discs or the LSDs ability to lock-up. Its a measure of the pre-load on the disc stack, which is induced by the disc thickness and the thrust/spring washers. Sure, as the components wear, the total stack height is reduced and the pre-load will decrease - but that does not mean the LSD will not lock up.

Best to open up the LSD and inspect the condition of the discs. They have a sintered type frictional surface on them, similar to a synchro. If they have worn thru the friction surface, galled, or burned, then they should be replaced.

rlets

Thanks for the info on the 951 tranny differing so much from the GT3. Mine is an AOR box so was planning to just replace the friction discs with OEM. My local tranny guru won't give me an estimate until he gets things apart for inspection.

Rich

Techno Duck

Anyone have an estimate on how many hours to rebuild the LSD? I also have an AOR Turbo S box that i was debating rebuilding. My local Porsche guru said he can do it, but i neglected to ask him for a 'quote'. The box has 120k mostly track miles on it..havent checked the breakaway torque but figure its worthwhile to do now while its out of the car. I have read that even with high miles, it doesn't mean the LSD is worn out, but i figured with the track mileage it might be.

Makes me wonder, 'while im in there' if i should have the synchros replaced also..

coilbox

Great info, thanks.

Is the Diff made by Porsche or by another brand?

Its an AOR gearbox, so parts are still available and only need fresh plates, from what I understand. Good news.

Also read that BMW´s E30 diffs have similar components, so that can be another source for the discs/plates.

http://e30performance.info/viewtopic.php?f=22&t=939

Oddjob

ZF


Do some homework on that before assuming it to be true. Since the discs have porsche part numbers (including 917, which is interesting), it is less likely they are a generic part used by an OE supplier on other brands. Often the generic parts have 477 part numbers or 016 (for VW/Audi transmission parts).

coilbox

I´ll try to confirm this.

Its good that ZF is the suppier, that means other brands could have similar diffs or replacement parts.

Thats includes cousin Audi, according to quaife the 944 diff is equal to the ones on the 4000 series. In fact the whole gearbox case is almost identical to that found in Audi 80. Too bad there all Torsen not plate diffs!

rlets

The 4k and 80 front differentials are open. The center diffs are manual lockers or torsens in transmisions that have a 3rd output flage at the tail. So it's really the other way around, the monster 4kq cars use the 944 LSD as the front diff. Makes for some odd handling but it does control the wheel spin. BTDT

Rich

Droops83

Perhaps I should have clarified, you need to remove the gear cluster from the bell housing as an ASSEMBLY to get the diff out. I agree that if you know what you are doing you can get the diff out fairy quickly, but it becomes a bit tedious when you have to do it several times back and forth when checking backlash after changing components.

If all of the bearings are good and nothing is being replaced (should be the case if you are rebuilding your stock diff w/ the same housing , make sure the shims remain in the same place and you will be OK). But, if either of the pinion shaft bearings are bad and are replaced, or if you are for some reason replacing any of the transmission case pieces, the bearing preload and pinion depth need to be checked and adjusted. Same goes with the carrier bearings for the differential. The ring gear backlash needs to be verified if any of the above are replaced. If you are installing a different differential (always wanted to say that!), it is also a good idea to replace the carrier bearings and set backlash.

Bottom line is, setting up these transmissions can be time-consuming if anything needs to be adjusted.

TonyG

I agree... I was only commenting on how easy it was to get the diff out.

TonyG