still more tranny questions
 

O.K. I've followed every test procedure I could find on this site for tuning the tranny on my 83' 300D but my problem still exists. At low speed and light throttle there is a very loud clunk on the 4-3 downshift. At higher speed and heavier throttle it will shift really nice. I've tried backing out the modulator and it seems like it doesn't do anything. Is the modulator bad? Any ideas? Thanks very much!

So you found the Steve Brotherton site and followed his advice?

Helo, I have a 1985 300D and had the exact same problem which I spent no small amount of time and money to fix. The culprit wound up being a small pin-hole leak in the vacuum diaphram on my turbo. The symptoms suggested to me that it could be a rear end going bad, bad center u-joint, or something else mechanical. I was amazed that fixing this vacuum leak corected the problem.
Good luck! Adam Bush

Yes I've followed the advice on Steve's site.

Any advice on how to go about checking for this vacuum leak at the turbo? My symptoms are exactly like what you descibe, u-joint or bad differential. I'm willing to try anything at this point. Thanks very much.

With your car being a 1983 model, you probably don't have the same diaphram that I have on the turbo, as mine is a cali model and it is for emissions.
The vacuum leak could come from anywhere, so I would start by working backwards, first starting at the modulator. I would buy a Mity Vac (or equivelant) and pull vacuum up to 20psi at the line going to the modulator. Then I would let it sit for a minute to see if it holds. Then, I would work this way backwards until I came to a "T" of some sort, and disconnect and plug anything not related to the tranny modulator vacuum while still ensuring the source of the vacuum to the modulator is still connected, then drive it and see what happens. Thsi is what I did and tranced it to that faulty diaphram on my turbo. I would bet that your problem is vacuum related as it seems the vast majority of tranny issues are.
I hope this helps, Adam Bush

Thanks Adam,

This is basically what I have started to do. I found a huge vacuum leak at the EGR and also at the thermo switch to the EGR. I've got that line that connects to those plugged for now. I've replaced most of the rubber connectors and vaccum lines as well as the vacuum switches and the bleed off valve. My modulator seems to hold vacuum just fine. I've even replaced the main brake booster vacuum line. I suspect my modulator may be faulty somehow, as I just backed it off one complete turn and it has only slightly improved the shift quality. I'm under the impression that the modulator is more sensitive than that?

Modulators are very inexpensive and are easy to replace, so it wou be a bad idea to replace yours. This would be a good time to change the filter and fluid if you haven't already as well.
There is also a shift improver kit that you can buy for 50 bucks which consistc mostly of springs inside the valve body. I have bought one for my car but haven't put it in yet. Maybe this weekend I will and post back the results - I bought it to fix the 1-2 upshift primarily.
Since you found the EGR leak, has the clunk on downshift gone away?

I currently have a vacuum leak issue with my door locks and if I do not lock the doors after getting underway I get some pretty abrupt shifts. Got to make the time to resolve it over the next couple/few weeks.

Since blocking off the EGR, adjusting the bowden cable and backing the modulator off one full turn the shifts are better but still not perfect. The clunk on the 4-3 still occurs, although not as frequently and all other shifts are smoother. However, it flaired on me at the 2-3 upshift the other day!!
Seriously considering going for a stick shift conversion!