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.

leathermang · #7 09-02-2004, 05:49 PM

Most everything that happens inside an Auto trans is controlled by very small orifices through which hydraulic fluid pressure moves stuff around..... like to engage the clutches , etc...
At $10-20 it is worth a shot up first..

pdxwaker · #8 09-03-2004, 12:32 PM

hmm... poking around last night & I found a drip from the transmission cover. I suspect improper torque on the cover nuts. Think I'll need to new cover to correct this drip?

Anyway, the fluid level had dropped since I first checked it. It is now below the 'fill' line. I'll top it off with trans-x and hope for the best.

One more question... I don't know the history or how long it has been since a fluid/filter change in the tranny so I was planning on a trans fluid/filter change w/Mobil 1. Should I add trans-x again when I do the change? If not how long should I drive w/trans-x before changing the fluid/filter? Or should I just do the fluid/filter change and add trans-x immediately (and not mess around with trans-x with the current fluid)?

leathermang · #9 09-03-2004, 12:43 PM

Since you are new to this car I would sure use the Trans-x ( but at the rate suggested on the side of the can... (find out how much fluid your trans has before you go to the store... ) it may take two cans to get the percentage suggested....
I would want the trans holes cleaned by the Trans-x ... then when I take the fluid out and put new fluid and filter I would feel much better about the condition of the inside of the trans.....ie, taking the old fluid out would evacuate whatever the Trans-X dissolved out of the valve body...