Well, things have been very good for too long. You know...you just start thinking that the car is running like a top and...I should not have tempted fate.

I have an '85 928 Euro with auto transmission and about 100,000kms on the clock. This evening I was out for a run and everything was fine...stopped for a light and pulled away normally. Everything was fine in first gear, but the shift to second produced a noticable rev of the engine, but little "go" in the transmission. Manually shifting produces the same symptoms...1st OK, 2nd slips, 3rd & 4th seem to work just fine. Problem only seems to be with 2nd gear at this point.

The car has no visible tranmission fluid leaks and showed full last time I checked (about a month ago). I have not had a chance to check fluid level or for any of the common signs of transmission failure (burnt trans. fluid, etc.) tonight due to darkness...will do this tomorrow.

Upon reflection, I do recall a slight slippage in 2nd gear when the car is very cold (say temp under 60deg F). This has been all the time I have owned the car...about 2 years. Almost imperceptable, but now it seems more significant.

Any thoughts on what to check or what the cause might be? Is this a common issue or just the sign of age - normal wear & tear. If a tranmission repair is in the cards, should I have it torn down locally or look to swap the transmission for a rebuilt unit?

Regards,
SteveCo in St. John's, NF.

 

It sounds like the rubber lip seals that compress the clutches are starting to fail. Age plus heat does make the rubber lip hard and that's why it slips when cold and then becomes ok when the rubber warms up. A new seal kit is in order. The clutch pack for second will also need replacing. Don't let it go too long before you start taking out hard parts. Gary

 

Garry, thanks for the guidance. I know a trip to the transmission shop is in the works...in fact the car is there now.

I was able to verify this monring that the transmission fluid level was low...add some and the car was marginally better but still slipping in 2nd when warm. Will run through the complete fluid level verification process this evening. The fluid is not burnt...looks very normal and in good overall shape.

Just trying to locate a transmission filter and gasket before having the mechanic drop the cover to see what's up inside. Are these parts 928 specific or can I look to source them from a Mercedes source? Reading the forum archives last night indicated that M-B parts might be an option. If not, I'll just order the right stuff...just hoing to cut a little time off the process.

 

Steve,

I have a filter kit for sale if you need one.. In fact, I have a complete Transmission if needed.

Good Luck,

Abby

 

Thanks, Abby. I'll give you a shout offline to discuss your stuff and acquiring it.

I have had a chance to pull out the repair manual and review the info on transmission troubleshooting. It has helped a bit with understanding what the problems may be. I'll go over it with the mechanic and we'll figure out what to do. As soon as I get an filter kit, we will open the unit up and see what we find.

I expect that I just have a transmission that needs a rebuild. Next decision will be whether to rebuild the unit I have or buy a rebuilt one and do a swap. I'd be interested in any experiences other owners have had with either process.

 

Steve,
I believe Steve C. our esteemed tranny Guru replied to a similar post within the last year.
I could be wrong, but there have been several posts concerning slippage in various gears at start, or, after warmup.
I recommend:
1. A dive into the archives.
2. Scope out the Greg Nichols site.
3. Filter/fluid change.
Wisdom - obviously not mine - from those with greater minds and more patience:
1.Make sure that all of the slack is out of the control cable, "tighter the cable the later and 'harder' the shift". Don't overdo it, you aren't reefing down on a guitar 'E' string!
2. If you do overdo it ...word is... you will lose the ability to manually downshift.
3. Adjust the vacuum modulator clockwise, to the point that there is no 'light slippage'on low power upshifts. There is a flip out 'T' handle - not sure if there is a cap covering it - that adjusts the modulator pressure.
4. Make sure you don't have a vacuum (hose)problem.
While you are under there check the short shafts for loose or missing hardware.
HTH
John S. and Pattycakes <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

 

Thanks for the advice...some great suggestions here. I have found much of the archive stuff you mentioned and have reviewed the repair manual info on the transmission too.

I am tending to just doing a transmission swap/rebuild, as I suspect the ransmission is on the way to the grave anyway. I would like to see if I can get some life out of it yet, however, so I might give your "tweaks" a try.

Any thoughts on what else I should replace if I decide to do a transmission swap? I have heard some references to rebuilding the torque tube at the same time as the transmission in the archives. Any other "might-as-well" items that I should know about?

 

Just thought I would report back and close this item off. After some investigation and troubleshooting, the auto transmisson was removed, disassembled and inspected by a local transmission shop with experience on the Mercedes-Benz auto unit. The verdict was that there was no physical damaged...just accumulated wear and tear that necessitated a rebuild. The transmission expert ventured that a shaky looking vacuum hose may have contribued, over time, to exxcessive wear during shifts...something that pre-dated our ownership of the car.

In any case, the transmission was rebuilt and reinstalled...seems to be working fine at present. Need to put a few kms on it to be sure and then inspect/adjust everything. We also took the time to pull the torque tube and replace the bearings with help from the procedure recommended by several people on this forum. The TT was in early stages of bearing failure and is now good as new. Very smooth and no low rpm bearing whine!

Only remaining issue is are non-functioning reverse/dask shift indicator lights. Looks like an electrical problem related to the transmission rebuild. I am in the process of tshooting this at present.

Thanks to all who offered help/advice. This is not an easy repair (never, never even think about it without the repair manual and a good reveiw fo the archived forum posts), however, once underway, it when very well. Much of the success was due to the help of some very skilled mechanics and contributors to this forum.

Regards,
SteveCo in St. John's

 

Hi Steve,

Did you have to remove all of the exhaust system and rear suspension to remove the torque tube and transmission? What were the costs involved? How much labor time was involved?
<img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

 

The entire rear drivetrain and exhaust system (from the headers back) were removed to liberate the transmission and final drive...this was a very big job. When the transmission was out, the torque tube was fairly straight-forward to remove and rebuild. I know others have done this work in a standard home garage, however, it is difficult to imagine doing this job without a vehicle lift and several other shop-type pieces of hoisting/lowering equipment. A healthy review of the forum posts and the repair manuals was in order before starting the job.

The work was performed by a local import auto repair firm that I have used many time in the past. They do not repair transmissions inhouse and had only worked on one other 928 before, but have serviced many Porsches both new and old (the closest Porsche dealer is in Montreal some 2000 miles plus an 8 hour boat ride from where I live. Interestingly, the "other" 928 needed a torque tube job too...which required much of the same work as our car did, so the shop had some understanding of the magnitude of the project. Even so, the car sat on one of their lifts for about 8 days in total. They had no big issue in performing the work.

On the costs (all in $Cdn, of course) here's what I can tell you. The repair bill for preliminary troubleshooting, removal/reinstallation of the transmission, torque tube removal/reinstallation and rebuild with parts in was just over $2,000 taxes in. The transmission rebuild was a further $1,500 (about $800 of which was parts). In total the job cost just over $3,500 taxes in (txaes about 15% here).

The only issue we have noted since the work has been completed is a modest moan in the drivetrain when the engine is under very small uphill load in 3 or 4th gear...speed is not a factor, although it is not detectable until the car is travelling 30mph or faster. Still not sure if this is in the transmission, final drive or torque tube. Release the gas pedal or pop the car in neutral and the sound instantly disappears...does not seem to effect the car in any way other than the sound, however. We continue to try to figure this one out...it is possible this noise was there prior to the "big repair" and we just have more acute hearing now...

Let me know if you need any more info.

Regards,
SteveCo in St. John's