nine-44

yeah, you have a R&P. I'm not too sure on the LSDs.. It makes sense but not. more traction=less slip and more load on the R&P or less slip and less hammering on the R&P because of not slipping?

Wade B

We discussed this somewhat at the GTG Sat. Andy has some good points about case distortion. That takes some of the voodoo out of the situation.

Realizing that it is just what I heard or read and is not really of scientific basis, I had always heard that this was just a metallugy problem with the factory R&P's only, just on n/a cars, mostly earlier cars, and that these problems were either non-existant or just rare when a R&P of "other origins" was used, say in the rebuild. My driving style has enabled my original clutch to last for almost 300K mi. but my tranny R&P went out at 120K. I didn't think anything about it because I had heard to almost expect it, at around that same mileage, due to what I said I had heard before.

I wish we had the finances/resources to have the metal analyzed in all of these R&P's or trannies we are discussing (or anyone else's who could submit a sample). Maybe we could conclusively, once and for all, cut through the hearsay, factory propaganda and conspiracy theories and arrive at the ultimate solution.

Then, maybe we could tackle who really killed JFK after that..........and then maybe Jimmy Hoffa........

tifosiman

I don't drive the car improperly. No big smoky clutch-dumps, and no powershifting/chirping.

The car is on it's second clutch, a centerforce unit, that was installed about 12K miles ago.

The last trans blew up when I was on the start line of an autocross, starting my third run of the day (had just done a hot second run about 10 minutes prior). I revved the motor to 2500rpm and let out the clutch (I tend to do slow starts since most autocross events here are rolling starts to trip the timer about 20 feet up) and boom! That's all she wrote. This was a rebuilt unit that was installed about 1.5 years ago.The transmission that died before that one broke on my way home from the grocery that was about 1 mile from my house under normal driving conditions. However it had done about 20 autocross events that season, one just the weekend before the implosion.

This is not a function of my driving style. I can say that without a shadow of a doubt. Those who think otherwise can wake up and smell the coffee someday when their n/a trans goes kaboom. It will happen.

I think that there is something inherently wrong with the r&p in these cars. Whether it is the case (Andy's theory), a metalurgical issue (my theory), improper pre-load/shims (ala the 968 problem), or some combo of these issues. Autocrossing cannot help, as there are very dynamic loads going on during an event (1st/2nd gear wind-up and wind-down constantly). Sticky race rubber and a good grippy clutch add dynamic loads on both ends. I'm not prepared to stop autocrossing though (although I have temporarily stopped for now until I finish building the stronger trans).

Installing a Turbo transmission will not be the answer. The gearing will be all off, it will make the car unbearable to drive at an autocross. (It might be OK in a daily driver that doesn't see "action", but that is not why I own the car) That gearing change is located in the r&p ratio, so even just swapping in a turbo r&p into an n/a trans is just as bad. So the n/a guys are stuck with the stock 3.89 ratio r&p. Provided that the r&p truly is the weak link and it is not the design of the case (boy I hope not!), then the only answer is to install a stronger/harder version of the 3.89 unit.

The LSD verses non-LSD is an interesting theory. I haven't done any research to that effect.

My impromtu search that I have done on Renn, Pelican, and the internet over the last few weeks, regarding 944 r&p failures shows that the overwhelming majority of them are pre-1988 model year cars, most non-LSD. I am not certain if this can be atributed to the fact that the mojority of the cars out there fall under this classification due to sheer production numbers, or if the switch in 1988 to the ROW trans for all cars stopped the issue.

If anyone would like to help me out, it would be nice to get some data here from Rennlisters that have blown the r&p in their n/a trannies. It would be nice to have a spreadsheet with the data on it. If you have blown an r&p in an n/a trans, please let me know the following:

Model year?
Mileage?
LSD?
Whether or not you autocross?
Condition under which it broke?

If anyone has their old trans or broken r&p, I'd like to see if there are different markings on those gears compared to a 88>onward car with the ROW trans. Thanks!




Jeremy

KuHL 951

I think I can already smell the 'coffee brewing' in my N/A. Backlash and gear noise seems to be on the rise especially under decelleration. I hope you didn't think I was questioning your driving style, I was just trying figure out why some folks get such mileage out of their R & P's. The database sounds like a good idea especially if replacement with a later R & P solves some of the problem. Makes me wonder if the fuel cutoff shudder on N/A's eventually wears out the mating surfaces. I wonder if the early Euro cars without the shudder have the same degree of failure?
Steve

tifosiman

Nah, I didn't think you were. Just a pre-emptive coment thrown out there for any future flack from others.

For any euro 'Listers, I would be curious to hear any data that they may have on their trans issues. According to Morgan and EWE the ROW transmissions were installed in those cars from 85.5MY cars onward, we got the ROW trans in 1988. I wonder how many post 85 euro cars had r&p trouble?

Spock 951

For anyone who isn't familiar with how differentials and limited slip differentials work, there is a decent description here: http://auto.howstuffworks.com/differential.htm

Based upon my understanding of LSDs, it isn't clear why they would be less prone to R&P failure than a non-LSD tranny. If anything, I would have thought that a LSD would provide less of a mechanism to relieve stress on the R&P than a non-slip, i.e., perhaps a wheel could spin more easily, and take some stress off the drivetrain, on hard launches with a non-slip. Another myth? It would be interesting to see the results of the informal poll on tranny failures.

Keith

Mighty Shilling

I love the smell of gear oil.

Waterguy

Porsche made it and put it in the 944S2. (3.875:1, actually.) Got to be cheaper to buy one 944S2 tranny than four NA trannies.

tifosiman

I hear ya, but the second trans that was in the car was an S2 transmission, according to the numbers on the case. That one lasted a total of about 14 months from the date of installation. It was probaby injured to begin with before it was ever transplanted, I guess.

At this point, whatever the next trans is that is going to go into the car has got to be right. I'm tired of tipping flatbed drivers.

inactiveuser92616

as far as testing for case flexion goes... I have an idea.
Find some sort of low tensile strength tape, (masking tape... postage stamps... etc)
and use this across various areas of the transmission that you think may elongate under flexion. If your tape is broken after a run, you probably have flexion. You might be able to do something similiar for compressed areas with fragile sticks that are well glued to the casing (JBWeld?)

Macfreak007

If no one else is going to say anything about a failed LSD tranny I'll just say that I had been autocrossing for about a year on my LSD tranny. I had not noticed any problems, I am crossing my fingers that nothing goes wrong next season, I am hopeful, maybe LSD is something to think about for your car Tifo?

StoogeMoe

How about adding what kind of tranny oil you were running?

schnellfahrer

The non-LSD tranny of my 1986 NA Euro exploded at ~62.000 miles. I did AutoX the car, but we're talking only 3-4 times before it blew. It blew while starting up in 1st gear. The road was wet and the wheels spun ever so slightly (but not much at all). I knew instantly what had happened, having read about it on RL several times. I never powershifted or did burnouts. I was the 4th owner. PO was an older man who never abused the car. The first owner worked for Porsche AG, the second owner I know very little about.

nine-44

Double check the # incase it had been swapped, but, you current trans should be an 88 trans Jeremy. I'm working on ideas for measuring case stress and distiortion.

josephsc

Jeremy -- interesting thread. Keep us posted on the rebuild -- I may be looking into something similar down the road. My tranny ate itself while downshifting from 5th gear during a "brisk" drive on the freeway after 5k miles of being mated to a 968 engine -- the cause is fairly clear. Out of curiosity, how much was the Powerhaus II hardened R&P?

Also surprised to hear that you blew out an S2 tranny, too. I thought that was supposed to be hardened like the turbo tranny.