my '80 300TD has been shifting really hard (it's worse when the engine's cold).
i don't suspect the transmission, because the previous owner told me he had it rebuilt recently, and when i recently changed the transmission fluid, everything was beautiful (no burnt fluid, no metal flakes, etc.)
i complained to a mechanic about the car shifting late and hard, and he told me to adjust the modulator until the car was shifting at the shift intervals marked on the speedometer, which i did.
HOWEVER, the car is still shifting hard, so the same mechanic has suggested that it must be a vacuum problem, and that the brake booster hose which supplies vacuum to the shifting mechanism is probably pulling too much vacuum.
does anyone know how much vacuum it should be pulling, and if there's anyway to know if the booster hose is the culprit, short of buying a new hose assembly for $75? thanks!
Lee

Too much vacume causes soft shifts not hard ones......you have a low vacume problem....check your rubber hoses....even the one at the modulator..if its not tight replace it.....you really need a vacume guage to properly diagnose or adjust this....

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

You might find this article to be helpful:
http://transmission.articles.mbz.org/adjust/

Is it shifting late and as a result hard or is the shift actually thunking? If it's just a late shift, I assume you have checked the kickdown switch? If it's thunking then that's different.

Is there any chance you have a picture of the inside of your air cleaner? I'm having issues.....

http://www.peachparts.com/shopforum/showthread.php?t=120526
air cleaner thread:

__________________
Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

I want to bypass all my switchover valves on top of valve cover and run the main vacuum source from the brake booster line to the vacuum modulator and then try to adjust everthing to spec. My question is what is the vacuum input side of the modulator is it the top or side of the unit.

The top is vacuum supply, the side is vent.