For kicks I bypassed the tranny vacuum amplifier and went for a drive. I connected the transmission modulator directly to the green damper on the output side of the VCV on the IP, capped the boost feed to the Y29 VSV and capped the supply line to the top of the tranny vacuum amplifier.

Result was much stiffer shifts at light throttle and noticeably but not objectionalby stiffer shifts at heavy throttle. I'll back out the modulator a notch or two to see if there's a happy medium. Oh, and I haven't checked that the VCV is adjusted per FSM procedure so that might make a difference. I'll also have to see if shifts are stiffer before the engine gets to 50*C. I think synthetic ATF blurs the difference in cold vs warm performance with regular ATF. We'll see...

140 Diesels, which don't have an amplifier, use the same VCV but a brown modulator in place of a black modulator. Not sure what color modulator is on late 300D 2.5s that don't have an amplifier.

Sixto
87 300D

Interesting, keep us appraised of your progress.

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
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"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

I find that on my car the shifts are always too firm. If I unplug the boost line going to the amp unit the shifts then become super butter smooth... actually much to slippy under lots of power. Does that point to the amp unit being defective?

-Jason

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
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What I didn't mention is I adjusted out the slack in the bowden cable before messing with the VCV. That ajustment alone sent shift points way up the rpm range and amplified the clunk into second when coasting in first under light throttle. The stacked 2-3 and 3-4 shifts was diminished at the cost of not shifting into 4th under 35 mph under the lightest throttle. Under heavy throttle, shift points were higher but not inordinately so. I should have checked whether first held closer to governor cut under WOT.

For the next test, I backed off about a third of the bowden cable adjustment when I bypassed the transmission vacuum amplifier. Shifts come at lower rpm. I'm going to back off another third or so because it still doesn't get to 4th soon enough to cruise at 35-40 mph. What's really odd about this setting is that I feel the upshift to 1st and the speedo pointer drops through 17 mph. This is the first time I feel an upshift in any MB. I don't recall feeling it when the bowden cable was tighter but maybe I didn't drive it enough. One more reason to adjust in more slack.

Ah yes, and cold shifts are oddly smoother than warm shifts which is odd because Y29 is out of the loop. Maybe a characteristic of synthetic ATF?

Still on the agenda is checking VCV setting and a couple of CCW ticks for the modulator.

Sixto
87 300D