87 300TD Hard Shifting, quick from 2nd to 3rd

[brooklyn]

Hey Guys,

Trying to sort out hard and quick shifting on 87 300td. Car will shift to 2nd around 3000 rpm, drop to 2500 and shift quickly to 3rd also around 3000rpm, which means I'm only ever in 2nd for a few seconds. Feel like shift points overall should be higher, up around 4000rpm.

Replaced fluid and filter (old fluid sludgy at bottom of pan) and replaced the transmission modulator valve, which seems to have increased vacuum pressure but will now "thunk", often on a downshift. Changes depending on how warm the engine is or if I've been driving somewhere where I can open it up for long stretches.

Is this a Bowden cable issue now? Any tricks to that? I understand one can adjust the Trans Modulator valve as well. Any suggestions on how to adjust that, or anything else, is appreciated.

thanks,

[brooklyn]

After searching around here, going to try adjusting Bowden toward me to delay shifts, and set VCV properly at WOT. Hoping to leave the Trans Modulator Valve alone.

From there, where? ALDA has probably never been touched on this car, but I'm a bit weary of messing with it. Heard it can help shifting issues.

thanks,

[Diesel911]

When mine Tunked on the downshift it was because I accidently dosconnected the Vacuum Line from the Modulator.

You might start from the begining and adust the Vacuum, adjust the Modulator perssure and adjust the Bodwen Cable.

Whan you replaced the Modulator did you replace the Modulator Pin? There is at least 2 threads I have read where they said that the Modulator Pin is easy to break.

Transmission Vacuum and adjustments
Mercedes-Benz Transmission, Steve Brotherton, ImportCar, February 2002

[Tubularfab]

Sounds to me like you have 2 distinct things happening. First, it sounds like you're seeing too little vacuum at the modulator (hard shift and thunking downshift) for a given throttle position. My car is missing almost all the vacuum stuff, and I've driven it both with full vacuum and zero vacuum going to the modulator. On the 2-3 shift I'm inclined to say you'll have trouble adjusting it out based purely on the fact that I haven't been able to on my '87 sedan yet. I have tried several adjustments of the Bowden cable, but cannot fix a quick 2-3. Right now if you hold the accelerator to the floor it shifts at 4700 each time. But, at low to moderate acceleration rates the 1-2 is good, then immediately after comes the 3-4 and it's rather annoying.

I've been in sponge mode reading every little bit I can find on here, so I'm suffering a little from info overload. But, seems like I read that there is an upgrade kit for these cars to fix the stacking? Required going into the valve body, but wasn't horrible to do... Have to go search some for that one.

[Tubularfab]

Finally found the post I saw. Check out post #11
http://www.peachparts.com/shopforum/diesel-discussion/286353-722-303-2-3-3-4-shift-flaring.html

[brooklyn]

Thanks guys for the info. I don't think I could pull off a rebuild kit right now. I think my vaccum is good, replaced pump and all the lines not too long ago. I think I over tweaked the Bowden cable because it revs to 5k now from 3-4, but at least I know it has an effect and helped with the quick shift issue. some more tweaking will help get the shift points settled.

I think I should get a vacuum gauge at some point, but I didnt do any kind of adjusting to the tranny modulator after installing it. Going to try a half turn on the T ccw to try and soften the shifts.

[calcars2]

I just bought a 87 300D 4K miles ago
its been well taken care of through out its life
now it seams to have an intermittent down shift problem in higher gears
last time at highway speed it wouldn't down shift at all ,staying at 5k RPM at 30 MPR- then the car died/ stalled ?? started right up and no shift problem??
yes it is Halloween ??
any ideas?