I went through this exercise twice. Both times the problems were internal to the transmission and required a complete rebuild. The transmissions functioned normally but gradually started to expel fluid. Fluid levels were correct and even my mechanic could not explain the leakage. Time to call the Mercedes transmission specialists. The AT is a non trivial device and most shops send their work out to the specialists.

If the leaks that you are experiencing are not solved by changing fluid levels, external gaskets, hoses, or seals, then you probably have problems which are more serious and usually internal to the transmission. Transmission fluid has extremely low viscosity and will creep from vent holes and along cases that will make it seem like the leak is coming from a particular location when in fact it is not. The leak might be higher on the case, perhaps from a vent hole, and have nothing to do with the point of drip. In fact hard parts inside the transmission might be damaged. Things such as scored governors and worn shafts can cause transmission fluid to be expelled after the car is parked. Torque converter seals can leak and build a sheet of fluid on the housing that will drip later.

If it comes to the point where your transmission requires R+R there are people on this forum who are near you and who are experts. Otherwise you might consider a guaranteed rebuilt transmission from one of the major 928 suppliers. Having the work done by the Pros has been worth every penny, especially when I read about the horror stories that have been posted.

 

Thanks for the suggestion borland.

Initially, I examined metal surfaces of the pan and the case. The pan's unpainted gasket contact surface is smoothly convex and has a slightly rough patina, like it was sandblasted with a very fine grit. This finish is consistent with the finish of the vertical walls of the pan's interior, and there are no visible defects or aberrations in this surface. The gasket clips into place on the pan rail, and holds it's place appropriately, in adherance to the metal.

The case's mating surface was clean and unmarred, and I cleaned it to a decent shine with a "Scotch-brite" pad. No irregularities and no damage was found on this polished surface.

The pan-stamping appears absolutely undamaged, in terms of evidence of impact and in terms of general deformity. The bolt pillars show no evidence of deformity, and stand-off distance, as measured with a straight-edge and feeler guage shows a gasket compression clearance of slightly more than 1mm at all pillars. A section of the gasket reveals a thichness of about 2mm, so there "should" be adequate compression. The gasket "appears" to mate completely around it's surface, and the thin gasket compound that I applied resulted in a uniform thin "bead" around the whole of the circumfrence of the gasket when I torqued it up. I would assume that the gasket compound would have sealed any minor ( and even pretty major) defect in the mating surfaces, since this is NOT a pressurized gasket application.

 

pappy, that is EXACTLY where I am right now!

I give up!!

I am now seeking a known EXPERT in this field. I don't mind paying TOP DOLLAR for EXPERT work.

But in Porsche-land, it is unfortunately easier to pay TOP DOLLAR, than it is to find the EXPERT.

Local referrals are eagerly accepted!!

 

Brian,

I sent you a PM.

 

Brian,
If the pan gaskets is leaking it can be because the pan bolts are tightened too hard - The specification said only 7 Nm (I earlier said 8, but today I checked) 7 Nm feels a nothing (normal for 8MG bolt is around 20)
Remove the pan and check the gasket for damages and the pan for evenness

 

Brian,

I was also wondering about the tightening sequence on the pan bolts - I don't know if how they were tightened (in any particular order) would make a difference as long as they were tightened to the correct torque.

If anyone also knows a NYC area tranny expert I would also like to get his info.

 

Doug, I wondered about the tightening sequence as well because the center pair's pan-rail is just slightly "high". I messed with center first and center last sequenced and saw no change in leak rate. Altering the torque value by 5 in.lb didn't make qa difference either, but altering it by 10 in.lb either way increased the leak notably.

 

Brian have you tried blowing compressed air controllably in the pans drain hole!-Might give you moe info. Spray the pan/case area down water/soap mix.Pressurize see what happens! Perhaps it might help!-Mike

 

Mike... do you know any 928 wizard in Edmonton??

 

ATRA shop locator and advice;

http://www.atra.com/consumers/trans_prob.htm

 

As a general inquiry, when installing the pan gasket, should you or shouldn't you wipe a layer of tranny fluid on the case when installing the gasket?

Mike, I thought of doing something like pressurizing the tranny to see if I couls notice a leak but was concerned about possible damage. I wonder if this could be done - I have an air compressor and the inside of the fitting which goes into the plastic tank is threaded so you could attach an adapter for this purpose.

Doug

 

No one! I'm sorry. If I did I would have told you 100 grey hairs ago!.-Mike

 

Hi Doug . Please don't do it until one of the pros here can confirm this wont hurt any thing.
ANYONE KNOW WHAT HAPPENED TO STEVE CATTENEIO?? Hes the biggest champ on these trannies.-Mike

 

Doug... the transmission does not normally operate under any significant internal pressure. VERY low pressurization might reveal the leak source, but it might push fluid out of places that were't leaking, too. Obviously, over-pressuring it could blow an otherwise healthy seal.

While I was under there, I noticed a SMALL amount of wetness in the area of the vacuum modulator valve. I doubt that it's the issue, but I'll replace the seal, anyway.

 

I believe that you can find Steve Cattaneo here;
http://www.mastertechtrans.com/index.htm