928 John

Hello All, I replaced the slipping 4 speed transmission in my '83 with a used transmission. This transmission has problems too! Can someone tell me what might be wrong? I'd like to avoid a rebuild if its a valve body problem or something.

1 - wants to creep in nuetral

2 - have to get revs up to 1500 to 1800 ish before she starts back

3 - "feels like" the further you go back the more resistance to motion
there is

4 - shifting second to third ( I think) revs go up 500 then drop then go up then drop. I'd describe it as 'hunting' for the gear. I can shift manually ok.

5 - trans got real hot in a half mile test drive around the block. Afraid to drive it again for fear of junking it.

Have only started it up once so details are a little sketchy (no pressures etc.). Thanks for the help John.

Big Dave

Steve Cattaneo is the resident transmission expert around here, and a great guy. Try searching the archives. You may find the answer before he replies if he sees this.

The "gear hunting" you describe sounds like a valve body issue (that's what happened in my case), but before you start looking for a diagnosis, have you confirmed you have correct fluid level? The car needs to be warm, running, in park, and level for you to check.

Mine was slipping, too. Performance improved when shifting manually. It eventually lost the entire ability to engage any gear, although it could move from park to neutral and back. I ended up with a new transmission.

I didn't have any of the symptoms you describe in items 1-3. Just #4. I'm not sure if my tranny was overheating.

SteveCo

As Dave says, Steve Cattaneo is the transmission guru. Search the archives and you will find lots of good info from him and others on the 4spd auto box. Steve helped me out alot and I learn in the process. Key points for the transmission are:

1. Fluid level (as Dave mentioned)...not to high...not too low.
2. Transmission operating pressure. This is critical to diagnosing shift and performance issues. If you have not checked yours, then this is the first thing to do (after checking the fluid level).
3. Shift linkage adjustment. These cars are finicky on the tension of the shifter cable. You should also adjust the operating pressure firm, then the sift linkage cable tension...not vice versa.
4. Transmission oil cooler. Can develop a blockage that effects pressure and temperature. Make sure that old trans fluid is pluged from the cooler when doing a fluid swap.

If you need local help, seek out a trans shop that repairs Mercedes auto boxes...the 928 unit is a MB box in a porsche case. Anyone used to MB autos will be able to handle your transmission just fine.

The Workshop Manual covers the operating pressure and shift linkage adjustment, but as usual, not in the detail that you will find in the archives or from Steve. It does have a good troubleshoot section, but first verify that it is setup the way it should be...

Hope this helps.

Regards,
SteveCo

928 John

Thanks Dave, Steve,
Funny thing about the level it was showing full (cold) and I had started it and run for brief periods. Then, on about the forth time, after it was shut off it pushed about a pint out the fill hole. It took a couple of minutes and it hadn't been run longer than b-4. Now at rest the fluid is right to the brim and just at the cold full mark when right after starting and running in nuetral.

Also the workshop manual says to put in about 8 liters and then start, add the rest. How? about 2 quarts seems to fill the pan to overfilling. i put in my couple of quarts ran it briefly cycled thru the gears shut her off toppeed it up, repeat-repeat repeat-etc.
Should I have added someplace else besides the red fill cap?
I can't figure how i'd add any more.

goodspeed928

The car MUST be running when adding!

928 John

Greg, Well... that certainly makes a world of difference. I couldn't get it to take that 8 liters or 10 liters the manuals talks about before starting so i was afraid to start her up w / o enuf fluid to run.

jpitman2

Go to www.mercedesshop.com forum and ask, there are some very good MB guys there who know the box.
jp 83 Euro S AT 47k

928 John

I was able to get the trans to drink a couple more quarts - level is now good.
BUT although shifting is good she still ;

1 - creeps in nuetral
2 - seems to get real hot
3 - 'binds up' after going back about 20 ' - when warmed up.

jp i'll give the merc site a try.

John Struthers

1. Drain that puppy and change the filter. NOW!
2. I would do the fluid change/filter first. Then adjust regulator pressure to a stiffer setting.
3. The overheating problem sounds like low fluid level which would cause overheating and consequent boil over/foaming which would then vent.

As mentioned above Steve C. is 'the man' for all your 928 trans. needs.
I'd bet that there are a few related problems causing the overheating, but the binding sounds more serious $$$$.
Do you have a whining/grinding/thumping sound under the car...TT bearings? That slipping has me concerned as well but you might get lucky.
Anyone know for sure about pulling the regulator and valve body without dropping the Transmission?
Good Luck.

928 John

John, Why the need to chnge fluid & filter so soon? Its brand new and i dont think its cooked yet. I figured on getting pressures and then a solution and then a f/f change?? John

BTW to acknowledge a previous post, I did flush cooler b4 hooking it to current trans. A tip I got from the archives - thanks.

928 John

What would cause the auto trans to creep in neutral? I think this could be a big clue as to where the problem lies. Shifter linkage seems correct , R and D are where they should be. John

Steve Cattaneo

John,
Assuming the linkage is adjusted properly .If the car what’s to move forward in neutral you have a bind ;meaning internal failure, planetary failure, stuck clutches in the drum, a stuck band or a sealing ring failure allowing fluid to apply a clutch drum. If you can not push the car forwards or backwards its mechanical other wise it is a hydraulic bind.the transmission is bad.




If you post on www.mercedesshop.com the best Mercedes forum, you will get the same answer verbatim.

928 John

Thanks Steve, I can push her back and forth. This binding seems worse hot. I think I'll post at the Merc site looking for a good local shop - here too I guess.
How important to you do you think additional diagnosics in the car will be. How much does Removal and Replacment add to the cost of rebuild.
If I pull it, send it to your shop, will a rebuild fix it? or might it be more involved?
Sorry about the vagueness of the questions.

SteveCo

You mentioned in your first post that you replaced a slipping 4 speed auto with a used unit. Could you not have the original transmission rebuilt (locally or otherwise) and then swap it for the used unit? Would seem to be the easiest way out if you still have the original transmission.

Alternately, you could buy a rebuilt trans from one of the Big 3 and do the swap...same results either way. They might be interested in the "other" used transmission as a core in either case.

Since you have replaced the transmission once already, the procedure is the same for a rebuilt unit (your original or a "new-to-you" one).

If you did not do it with the first swap, consider rebuilding the torque tube bearings and replacing the torque converter bearing at the same time. More cost, I know, but easy to do now...difficult to do later. Watch out for engine thrust bearing failure after the transmission/torque tube rebuild either way. More on the archives on this one.

Regards,
SteveCo in St. John's

928 John

SteveCo, The orig. trans seems to be bathed in metal particles internally and I "monkeyed" with the valve body (wrong parts wrong places?). The used trans I gambled on and lost "seems" in better over all shape and will have to come out one way or another.

Thanks for the suggestion John