Kaosii

Anyone have any experience rebuilding their limited slip diff?

I autocross my 1985/2 944 regularly, and have been noticing some inside wheelspin on slow corners.

I pulled my trans apart, and my diff apart to have a look. The clutch discs do not appear to be severely worn. Anyone ever torn apart a limited slip that needed to be rebuilt before? What does a bad one look like? What should I replace while I'm in there?

The porsche parts catalog lists different thicknesses available for the external spline steel disc 917.332.552.11 (1.9mm 2.0mm 2.1mm). It seems that mine has the 2.0mm disc. The surface looks polished from wear, but there is no measureable wear groove. If I purchase a new 2.1mm disc, will this increase the spring pre-load and hence lock-up?

Also, the internal spline disc 917.332.551.10 - what kind of material is this? I have rebuilt a Ford trac-lok LSD before, and the Ford discs have a friction material bonded to them similar to a clutch. The Porsche disc does not seem to have any bonded material. Does this mean it has worn away completely? Or is the disc made of some sort of wear resistant material? (kind of looks like powdered metal to me)

The porsche parts catalog also lists part #951.332.551.00 as a replacement for the 917.332.551.10, along with a new pressure ring (951.332.511.00). If I use the replacement 951 part number, is a new pressure ring absolutely necessary?

I'm hoping to find some experts here.
Any help here would be appreciated.

Jon

GOBOGIE

Bump

Ben Z.

Jon-

I'm surprised nobody has offered any opinions yet. Maybe people are shocked that a new poster would ask something other than "Where do I buy the parts I need to beat my friend's civic in a drag race?" Anyways, welcome to Rennlist!

Sorry, I know next to nothing about these differentials. I do know that people have replaced them with gear-type LSDs, they are pretty pricey, though. A search on LSDs might be useful (upper right hand corner).

944S2NUT

www.quaifeamerica.com Try these guys.

pametnikurac

Ok, you have to take yours appart, and mesure the plate that has 4 protruding squares on the outer diameter, you have to measure this 2 plates for thickness, they will probably be 1.9 mm, you can buy thiker plates directly from porsche up to 2.2mm i believe, plus is aldo important to change the disks (2) that go next to these plates , the sping (diafragm) and the trust washers, I hope this helps, i am doing this wor on a diff to put in the back of my audi s4, (yes your diff and my diff are the same) and iI had to strudle to find this info....

pametnikurac

yes i forgot to mention this increases the preload thus increasing the lokup i have been tol that with the thickest plate you can accieve a 60% lockup

Bryan

You might also want to consider taking a step back and considering just buying a clean, used LSD transaxle from a car that hasn't been autocrossed. There are an awful lot of 944s from that era in the junkyards these days, so you should be able to find an LSD transaxle in excellent shape for cheap money.

I'd just hate to see you buy the parts for this thing, put it all together, put it back in the car, and have it not work. Then you have to pull it out and apart again....etc.

Bryan

Sam Lin

Bryan, the problem with buying a used LSD is that as old as these cars are, any used unit is almost certain to need rebuild anyway. It sounds like he has the ability to rebuild his, which will result in a far better LSD than any used box when he finishes, for less cost on his part.

Sam

porshhhh951

hmm....sorry man i wish i could be of some help........maybe this will make you feel better......i have 2500.00 in my lsd.So if you can have yours done for a fraction of the cost kudos to you.I think someone already posted a link to where i got mine at so....enjoy and i hope everything go's well with your rebuild

fyi mine is a 1.5.

Kaosii

I appreciate all of the replies.

Here is a little more background on what I am doing.

I purchased my 1985/2 944 four years ago, and have been autocrossing it for 3. Three years ago, I rebuilt the transmission with all new bearings and synchros, mainly because it was grinding into second when driven hard (and shifted quickly). While I was in there, I decided to install an LSD. I bought the unit used, with unknown mileage. I did not take the LSD apart at that time, but was assured by the seller that it was in excellent shape.

Fast forward to now. I am transferring the LSD to an '88 924S. Like I said earlier, I have noticed some wheelspin on slow corners while autocrossing. Of course, I use sticky Hoosier tires, and regularly see over 1.15g cornering in the car (with completely stock suspension). So, since I had to take the diff out to transfer it, I decided to have a look and make sure everything was kosher inside the diff. Well, now that I have it apart, I can't tell if it's toasted or not. I would say that at first glance, there is only minor wear. I could just replace the clutch plates and the conical preload washer, but that would cost about $200 in parts. I have better places to spend the $200 if not absolutely necessary.

I suppose I could just slap it back together without replacing anything, but then again, if the diff does decide to catastrophically fail, it will take the trans with it.

As for the time spent jerking around with these transmissions, I have gotten very good at removing them. It takes me about an hour and a half working by myself in my garage at home. Takes a little longer to get it back in though.

pametnikurac, how much wear was on your audi unit?

Sam Lin

Kaosii, the diff won't "catastrophically fail" even if it is really worn - you just won't have much LSD effect - especially if you autoX or track a lot, the benefit in lap times from rebuilding the LSD and increasing preload for $200 is the best $200 you can spend, if your price is indeed that low.

Sam

Kaosii

I will admit that it is probably rare for an LSD to catastrophically fail. I guess I am just a little gunshy now that the differential in my Ford F-150 catastrophically failed.

I installed an aftermarket trachtech truetak diff into the 8.8" solid rear axle of my 1997 F-150 tow vehicle. This diff functions in the same manner as a Torsen or Quaife diff - there are no clutches to wear, and the limited slip action is performed by the friction generated between the worm gears. I had the unit installed for nearly a year, and was on a road trip towing my 944 home across the country from an auto-x. While still a good 10 hours from home, (and 14 hours into the road trip) the diff started making a strange squeaking noise. It sounded pretty serious, so I had to pull over and stop for the night, getting a hotel room. The next morning, I pulled it into a local shop, and had them tear it apart to have a look.

What I found inside the diff casing was very disturbing. There were bits of ring and pinion everywhere. A complete disaster. On closer inspection, It appeared that all of the bolts holding the diff together had sheared off. The bolts then went flying around inside of the case, taking out the ring and pinion. Since no new parts were available in a reasonable amount of time, I just had the mechanic remove all of the broken bits and slap it back together. I managed to limp home at a slow pace.

When at home, I sent the differential back to the company I purchased it from - Reider racing here in the Detroit area. They were very helpful, and I received a full refund from the manufacturer through them. The true cause of the problem was that the bolts holding the diff together had been overtorqued at the factory. So, the bolts had enormous preload, and had stretched. The additional tension forces on the bolts generated from the differentiating action caused the bolts to overload and fail. Unfortunately, the warranty did not pay for the ring and pinion, and all of the bearings and seals that went south as well. As kind of an odd twist, the failure occured 1 day after the 1 year warranty expired. Fortunately, it was still covered.

So, I decided to purchase a different type of differential from a different manufacturer, as I was obviously not too impressed with the Trachtech quality. I bought an Auburn differential to replace it. It was the same price, so the warranty money covered the cost. The Auburn is sort of like a clutch type limited slip, but uses a cone type of clutch instead of flat plates. This works in sort of the same manner that a synchro in a transmission works - a male angled concical surface mates to a female conical surface. The Auburn has since served me well, and comes with a four year warranty. Unfortunately, it does not seem to function quite as well as the Trachtech did, as I now experience more wheelspin.

So, as you can see, I am a little nervous about the diff. I think I may have just talked myself into the $200 rebuild.

Anybody else have any horror stories?