I've got a 91 350 SD with 265,000 miles on it. The transmission shifting was a mess, so I've been going through getting everything adjusted.

The symptom I'm still working on has to do with low speed downshifts. Right now the transmission shifts very nice on full and part-throttle accelleration. But when coasting, it starts downshifting noticibly. Not with a clunk, just with a smooth downshift you can fell sorta push the car. Downshifts at around 45 or so. Problem is at lower speeds, say at around 25 to 30 mph it has downshifted a little too far. When you are in traffic and have to give it some gas again, it is stuck between gears and flares strongly as it hunts for the gear it should be in.

What I've done so far:

Transmission is serviced, has correct fluid level.

I took up the slack from the bowden cable, adjusted the slider as well.

Adjusted the VCV according to procedure in the FSM.

With the modulator vacuum removed, the car shifts perfectly at full throttle. Shifts right on the marks on the speedometer, nice and firmly.

With the modulator vacuum in place, still shifts nicely at full throttle. Right when it is supposed to. I have not checked the transmission pressure since havn't found what the pressure is supposed to be on this 722.361 tranny in this car. (Anyone have it in their docs?) When I pull a vacuum on the modulator, it holds fine. I suspect the modulator will be ok, since it seems to shift nicely.

What I'm trying to figure out is what the vacuum pressures should look like. The VCV has around 13 inches at idle, this goes to zero at full throttle.

At the blue amplifier the modulated pressure to the transmission starts at around 16 inches. At full throttle it goes down to 4 inches. No lower.

This is where my questions start. Does this range sound correct, 16 - 4? Or should there be a boost signal present or something that takes this on down to zero? I suspect I'm not getting a boost signal.

I have search the website and manuals, but have not found a description or vacuum diagram that I think fully explains how this is supposed to work in this particular car. Any help greatly appreciated.

Don

__________________
1991 350SD 265,000 miles
1981 300D 320,000 miles

1990 350SDL 144,000 miles (wrecked)
1991 350SD 225,000 miles (sold)
1985 300D 113,000 (sold)
1987 300SDL 183,000 (sold)
1984 300D 360,000 (sold)

To me it sounds like the Bowden cable is too tight. Give it a couple of turns and provide more slack.

Drive it and see if the early downshifts disappear.

It's not a vacuum issue.

Hmm.. When I started the bowden cable was WAY too slack. Like you had to take the throttle up over half way before it would start to pull. I'll work with it.

Still would like to know what the vacuum range should be with this setup.

Don

__________________
1991 350SD 265,000 miles
1981 300D 320,000 miles

1990 350SDL 144,000 miles (wrecked)
1991 350SD 225,000 miles (sold)
1985 300D 113,000 (sold)
1987 300SDL 183,000 (sold)
1984 300D 360,000 (sold)

The boost signal should take it down to less than 2" or so. But, the fact that it does not is certainly not your issue.

If the shifts are not unreasonably harsh, the vacuum is fine.