300D 2.5 rough shifts - vacuum questions

[pdrayton]

I'm guessing that the reason my 92 300D 2.5 Turbo W124 bangs into gear is because the vacuum going to the tranny is too low.

At about 1/4 throttle the vacuum drops from 10" to about 5". At half throttle it is near 0". I have checked for vacuum leaks - haven't found any. I don't think there are any because the vacuum level is correct (10 inches mercury), and is the same when the tranny is connected or not.

The vacuum valve does make a buzzing sound when it is dumping vacuum though, and I don't get any vacuum at the "ventilation" port on the side when it is dumping. Maybe it is buggered? If so, it seems strange that it provides a smooth (albeit exaggerated) vacuum control.

I have changed tranny fluid and filter (mobil 1 synth) and the results are the same. The car shifts perfectly at low throttle (which makes me think the vacuum modulator is set correctly).

I took the vacuum valve off to look at it, and it seems fine - by that I mean the amount of vacuum seems to correspond to the position of the thing that turns it on the injection pump. That thing (wassit called?) seems to turn a lot for a little throttle movement at low throttle and then reduce how much it turns.

Anyway, I did the accelerator linkage adjustments from the FSM and everything was in spec.

The only thing I noticed out of place was the vacuum diagram for this car doesn't match exactly - instead of splitter coming out of the vacuum source to the vacuum valve, my car just has a single line. I'll attach the vacuum diagram with a note where the problem is.

Any help with this would be GREEAAATLY appreciated. I have been trying to fix this for months (on and off). I've got pretty much everything on this car going great. It's just the rough gear shifting that is the problem.

Thanks!