'87 300D No Upshift - PeachParts Mercedes-Benz Forum

Duncwarw · #1 07-13-2010, 11:52 AM

Hi Folks.
I can't find ANYTHING related to the transmission on the CD I have.

My car won't automatically shift into top gear. I can to idle, put it in neutral for a second, and back in drive. Then it shifts. Otherwise it will just hang in 2nd.

Is there a vacuum modulator? I'm off to get it on the ramps but any insight will be gleefully received.

Thanks

vstech · #2 07-13-2010, 12:06 PM

try searching for B2 piston repair.
I believe you are describing early stages of this failure.

BoiseBenz · #3 07-13-2010, 12:27 PM

It's not a B2 problem--that's when the car won't start moving.

Most of the ATSG manaul troubleshooting items nearest your complaint point to governor/pressure or valve body issues. I suppose it could also be related to the electrical kickdown switch/solenoid.

Did this suddenly start? Has it always done this but then recently got worse (especially when X happened)? You just bought the car and have no idea of history? Does it only do it when you floor it, or only at half, or every time no matter what?

I would suggest that random adjustments (to Bowden, modulator, or amplifier) are not the proper corrective action.

babymog · #4 07-13-2010, 01:21 PM

There is a switch (downshift button) under the gas pedal on the floor, un-plug it to see if it was sticking and preventing shifts. If that is not it, check the "bowden cable" or downshift cable leading from the throttle linkage to the transmission, it should move in/out easily and return to rest when the linkage is at idle.

Duncwarw · #5 07-13-2010, 01:56 PM

Thanks all.

It just started in the last few days.
I've done nothing in the last few weeks other than bypass the over boost switch and that was some time ago.

It doesn't seem to matter how hard I push it, it seems to do the same thing every time. It does the first two upshifts fine. It simply refuses to do the last.

Oh, and to answer the other question, we have had the car for maybe 4 years but we have no knowledge of what was done before other than the maintenance log in the owner's manual. It appears to have been well maintained and all work was done at the stealership.

Duncwarw · #6 10-13-2010, 01:55 PM

It was pointed out that I didn't post the "fix" on this thread.
Thanks to the poster who reminded me.

I changed the transmission filter and the problem vanished.
There's another thread where I got great help on this entitled
"Shifting All Over The Place".

Thanks