Tanny shifts too soon. Not cable? - PeachParts Mercedes-Benz Forum

imdavid28 · #1 05-07-2006, 10:17 PM

Ok, so here is the problem with my 82 300D: The transmission shifts way too soon for all gears regardless of petal position (maybe not wot, havn't tryed yet.) You take off from a stand still and it almost immediatly shifts to second, third, then fourth.

I tried researching this problem on here and people had mentioned the kick down cable needing to be adjusted. I checked mine, and it is all the way tight, which should cause it to shift high, not low. For a sanity check I also adjusted the nut to the other extreme: no difference.

Next I checked to see if the cable felt broken; I disconnected the cable from the linkage on the valve cover, pulled the boot of the bracket (just to make sure) and yanked on the cable. It felt like it was still connected to something.

Is there something I am missing? Any Ideas?

RichC · #2 05-08-2006, 04:21 AM

Hello Bob

My 81 300D was doing the same thing. It was a vacuum line leak.

Try this link to one of the DIY's for more info on the vaccum control system

http://www.peachparts.com/Wikka/TransVacTune

Hope this helps
RichC

#3 05-08-2006, 04:27 AM

Did the cable pull back (spring back) when you pulled the head?

Check your fluid level, color and last time it was changed.

If it's not been changed in a year or 20,000 miles, it might be a good idea to pull the pan and check for metal in the filter.

rhodes2010 · #4 05-08-2006, 11:21 AM

RichC is right about vacuum.
After the cable is checked the vacuum needs to be working.
If I remember correctly, low/no vacuum causes the early and hard shift.

I had same problem. In my case the cap on the modulator ($2.50USD)
was leaking.

With a vaccum tester on the modulator line - it should hold and not leak.
Connect to line to modulator with engine running at idle, you should have vacuum coming from engine.

SD Blue · #5 05-08-2006, 11:31 AM

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

#6 05-08-2006, 11:36 AM

Vacuum should only change how hard/soft it sfits, not the time. That's the job of the cable.

mplafleur · #7 05-09-2006, 09:26 PM

Mine does the same thing. So I manually shift it now. And that's with the bowden cable disconnected. If I connect it, it won't shift until > 3500 rpm. That's at all bowden cable adjustment positions.

imdavid28 · #8 05-10-2006, 08:35 PM

Yesterday I did a filter swap and everything looked fine; the fluid wasn't burnt or sparkly, no metal peices in the pan or anything. It was slightly overfilled before, and I do believe I did the same thing again this time, but I imagine that can't be to terrible, can it?

I also checked the vacuum side of things as well. First off, not knowing any better, I had bypassed the trottle valve, so I rerouted it correctly. There was a leaking hose on the modulator valve, which I replaced. So now it can pull/hold a vacuum.

After all of this there is no real difference. The firmness of the shifts vary with throttle possition, but tt still shifts too soon

Any more ideas/suggestions?

imdavid28 · #9 05-10-2006, 08:37 PM

Quote:

Originally Posted by ForcedInduction

Did the cable pull back (spring back) when you pulled the head?

Yeah, it does spring back. Is there a spring somewhere in the cable assembly that could be doing it though?

#10 05-10-2006, 09:12 PM

Quote:

Originally Posted by imdavid28

Yeah, it does spring back. Is there a spring somewhere in the cable assembly that could be doing it though?

It should spring back. I wanted to see if the cable was broken.

SD Blue · #11 05-10-2006, 09:58 PM

[QUOTE=imdavid28]......... It was slightly overfilled before, and I do believe I did the same thing again this time, but I imagine that can't be to terrible, can it?................QUOTE]
These transmissions are very sensitive to fluid levels. As to whether that is the sole reason for shifting too soon, it is hard to tell. Maybe so.

Have you gone through the tranny adjustment sequence from MBZ.org ?

imdavid28 · #12 05-11-2006, 09:27 AM

Yikes, I will drain it down to the correct level today when I get home and then go through that adjustment sequence step by step. Thanks for your help!

mplafleur · #13 05-13-2006, 01:35 PM

Found a vacuum leak where the plastic vacuum line connects to the transmission vacuum amplifier. I replace the connecting rubber line and then reconnected my bowden cable. Now all shifts fine again!

Diesel Giant · #14 05-13-2006, 01:44 PM

Excellent!