rpcarrier

Hello everyone, New to Rennlist and hoping to get some help. I recently purchased a beautiful, all original 1983 928. The vehicle is immaculate. It has a differential leak coming out of a weep hole between the tranny and the differential. It has been in a qualified repair shop with a solid reputation since December. The differential has been resealed three times using all oe Porsche seals and O'rings. The case has been thoroughly inspected for any blemishes, cracks and imperfections with none found. Every time it is reassembled the leak resumes after 2 days just sitting in place. It is a sizeable leak. They are baffled and about to issue a refund with instructions to send it somewhere else. Has anyone every had such a problem with a 928? I found a limited slip differential for a 1979 928 and I was wondering if it is interchangeable with an 83 year model. Thanks for any help!! Randy

James Bailey

OK so you have an automatic transaxle is the leaking fluid red or is it blackish stinky stuff ??

rpcarrier

Its 90w black stinky oil. Transmission doesn't leak a drop. No red oil anywhere.

James Bailey

I suggest you call Greg Brown at Precision Motorwerks and get his opinion. He has more experience with 928 transmisions than anyone else I know. I had hoped he might have posted to this thread already but is probably too busy fixing 928s The 78 and 83 used different transmissions 3 speed vs 4 spds but not sure if that also changed the differential housing......

GregBBRD

There is an "intermediate plate" between the Mecedes automatic transmission and the Porches differential. There are two rather expensive seals in this plate....one to stop the automatic transmission fluid and one to stop the differential fluid. There is a hole machined between these two seals which vents either fluid to the ground, if one or the other seals fail.

from what you are describing, it sounds like the differential seal failed and gear oil is coming out of the vent hole.

These seals are robust and very infrequently leak....I've never had a new one leak.

Several possibilities....what gear oil are they using? There are several gear oils that leak past new seals. The fact that the leak occurs after sitting is very, very strange. The automatic differentials have a different rear cover, with a lower fill plug, to keep the gear oil from "resting" on that seal. Are you certain someone didn't replace the rear cover with one from a manual transmission? This, combined with a fluid like Redline, would most likely allow fluid to leak out that seal.

Did they replace these two seals with the correct factory seal? Are they installed in the correct direction? (They are backwards from what one would initially suspect.) Did they replace them both?
The seals need to be really square. (I have a special tool I made to install them.) And finally, the two seals each have "nubs" on them to limit the installation depth and allow the fluid to escape. Did they recognize this and line up the nubs with each other?

​​There are two O-rings on the pinion to keep fluid from seeping down the splines and seeping out. Did they see these and replace them?

BTW...."qualified repair shops" that can deal with b the intricacies of the 928 vehicle are few and far between. "Qualified repair shops" that can deal with the intricacies of the 928 automatic transmission are virtually non-existant. If they are actually "qualified" to do this job....they are an "amazing" shop!

I know these things inside out and upside down.....in the dark....and I just had one that I had out 5 times to figure out a really obscure (and multiple source) problem. They are old....and problems from age are becoming more common.

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rpcarrier

Thanks for the help Greg and James. The leak was found and it is exactly what Greg stated. The seals had to be ordered from Germany and the repairs are now being performed by a Porsche technician. It has to be done through an independent shop because the two local Porsche dealerships will not work on the car because of its age. The technician performing the repairs has been with Porsche for many years. Kindest regards, Randy

GregBBRD

Fantastic that you've got it under control!

dr bob

Interesting. Porsche has been pretty actively marketing their "Porsche Classics" program down through dealerships. Our local dealer here is more than willing to work on older models. They host the local PCA regional meetings, and the service guys often come out to see the older cars that are driven in for our monthly dinners. Often, the cars are a bit older than the service guys though.

Finding a "factory-trained" 928 tech at a dealer or an independent is bordering on impossible. Dealers offered techs for model-specific training as part of a progressive training program. Those typically started with the equivalent of an apprenticeship, then on to an escalating journeyman-equivalent program that introduced techs to systems training before they received the model-specific stuff. "Master" status is rare, and happens at the end of all that. A very busy/large dealer might have two or three "master" techs, and they weren't young guys at the time. Add thirty years or so since the training centers offered 928 model-specific instruction, and figure out that program survivors have retired or moved on. I think I can safely say that there are none younger than sixty to sixty five today. Meanwhile, there's no doubt that there are "factory-trained" techs out there that have been through a few or many of the system training programs, and maybe some model-specific stuff. Just not for the 928.

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I had the timing belt and water pump changed on my car before I picked it up from the seller in Denver about 20 years ago. The dealer tech who did the work had been through 928 model-specific training. I brought the car home to the Los Angeles area, and had the dealer near my Pasadena office do the belt tension check. Coincidentally it was the dealer than had originally sold the car new to the PO. They also had a master tech who had been through 928 model-specific training. But that's not who did the work, unfortunately. It was pushed off on a less-qualified tech even though I'd discussed all this with the service salesman in advance. That episode was a tipping point for me. The only non-Bob attention the car has seen since purchase was for wheel alignment, and that episode got onto doing my own alignments too after the car quickly ate a set of tires with the "pro" alignment. Rob Edwards worked with me on the intake refresh project, and I trust him more than I do any dealer or independent who might claim "factory trained" status. A few others here on the list are known 928 gurus, totally qualified to work on the cars. To my knowledge only one of them might have 928 model-specific "factory" training.

rpcarrier

Well all that you say is a bit scary. I can only hope the person working on mine is as qualified as I was told but where I live it is difficult to find anyone willing to work on any Porsche and especially a 928. I cannot answer as to why the dealers closest to me are unwilling to work of the car, if Porsche is indeed actively promoting the "Porsche Classics" program as you say. A coworker of mine who has a much newer Porsche called the dealership who tends to all of his service needs. He was convinced that they would be happy to work on my 928 and to his surprise they refused. He is a regular customer in good standing and it made no difference. For obvious reasons I will not publicly place the names of the dealers on this forum but if you would like to contact me privately I would be glad to provide you with the names of the 2 dealers and you can call them at your convenience and have them explain their reasoning to you. I am not interested in bringing it to them if they don't want it. My car is in impeccable condition therefore condition could not be used as an excuse. At this point I don't really care if the dealers I have access to do not work on my car. I just want it fixed once and for all. I am further puzzled because I never requested any sort of an estimate. I was willing to pay any reasonable amount necessary to fix it. I am forced to wonder if some dealers can opt out of the Porsche Classics program. I see that you are from Oregon. Interestingly my car was purchased brand new in Oregon. It was sold to a gentleman in Seattle who I purchased if from. Well thanks for the input, at this point I can only hope that I will soon have my 928 fixed. I have decided if it doesn't get repaired on this next attempt I will rely on the good people in this forum to recommend a good place to have the vehicle shipped to. I will hire an enclosed carrier and send it off. Thanks Kindly Randy