Shifting woes - PeachParts Mercedes-Benz Forum

pdxwaker · #1 09-02-2004, 11:15 AM

I just picked up a high mileage (317k) '83 300DT and have been going through the car fixing typical problems (dash lights / door locks / etc.). The car has a strange shifting problem that I haven't seen before... I haven't found any similar problem using a search (though I'm not sure if there are better keywords to use).

The car will sometimes buck back and forth between 2nd and 3rd. It kind of hangs around 3000rpm and revs up/down like it is thinking about shifting. If I let up off the accelerator it will shift and I can continue driving. Otherwise it seems to shift pretty well (though it sometimes revs just a bit before it catches first gear).

I've been trying to troubleshoot the tranny vacuum system and haven't found anything obvious (though I'm still a rookie this). Any tips for me on this one? Kickdown cable?? One more question... the car had a serious vacuum leak in the door lock circuit. Can this affect shifting? I isolated the problem and plugged the trouble area last night (until I can fix it properly) but the shifting problem still exists.

Thanks for any help!

-John

leathermang · #2 09-02-2004, 12:17 PM

Do a search for Trans-x.....

pdxwaker · #3 09-02-2004, 01:57 PM

did the search... from what I read it sounds like you think I have problems internal to the transmission, not something that can be fixed with an external adjustment like I've read about here:

http://transmission.articles.mbz.org/adjust/

Any other thoughts?

Tirebiter · #4 09-02-2004, 02:14 PM

Use the trans-x, it's good stuff for internal goo buildup.

Set the pressure at your modulator too. This often helps to overcome the internal leakage in an old, well used transmission.

With a high mileage unit like that one, be prepared for a rebuild or a replacement.

pdxwaker · #5 09-02-2004, 02:57 PM

I can give trans-x a shot... can't hurt. I just haven't been able to find a similar problem description during my forum search. Lots of 'flaring', 'slipping', 'early shifts', 'hard shifts', etc. but nothing like what I described in my original post.

-John

kerry · #6 09-02-2004, 04:08 PM

Vacuum leaks can definitely effect shifting although I don't know if they can produce your symptoms. When I had a pod leaking in the heating system, downshifts were really hard when the heater was on. You probably need to T in a vacuum gauge to the line to the tranmission and monitor the level of vacuum.