Hey everyone I have been all up and down these forums and I am having my first tranny problem on my 1985 300SD. Iv read alot of posts about 84 and previous models, but the vauum system seems to be a little different on my model.

Shifting up from 1-2-3 and 3-4 makes the tranny kind of slam into gear. Sometimes its better than others but there is noticeable force coming down on something.

Also, when i come to a complete stop, there is a loud clunk that seems to be coming from the rear differential but could very well be the tranny. this clunk happens when going from 4-3-2 to a stop.

My mechanic has told me that I do not have any vacuum leaks.

HERE IS THE CATCH

I had been having heater problems and I ended up pulling the #10 fuse. When I removed this fuse, THE TRANNY STARTED SHIFTING FINE LIKE NEW! This fuse controls the climate control as well something called "automatic transmission electronics". I would have kept the fuse out to keep my tranny shifting right except the heater continues to blow even with the unit switched off.

When I reinstalled the fuse, the heater started working properly and unfortunatly the rough shifting and loud clunking returned. This is why i dont seem to believe i have a vacuum leak. Alot of the info out there is for model makde before mine so Im wondering if anyone knows whats going on here. I am a commuting college student and I love this car, I need this car to run right.

Thanks ahead of time!

You may not have a vacuum leak, but, clearly, you don't have proper vacuum going to the vacuum modulator on the transmission.

And, yes, the '85 is a different vehicle and has different controls as compared to previous models.

I'm not up on the details of that vehicle to provide specific advice on fixing the vacuum problem............whatever is controlling the vacuum to the transmission is not functioning properly.