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

 

From what I've been told the modulator controls the firmness of the shift and the Bowden cable controls the shift points. In other words, if it is shifting early or late adjust the bowden cable (located at the throttle). If it is shifting hard (and it should shift a little hard) adjust the modulator.

Here is a great series of articles from www.mbz.org
follow this link:
http://transmission.articles.mbz.org/

Good luck and please let us know what you do to repair it (it helps us to know what finally solves a problem).

Tony T

 

Tonkman is correct. But it is possible too that there may be a vacuum leak to the modulator valve. Follow the vac hose up from the mod, better yet, get a Mity-Vac and test for vac leaks from both ends, vac amplifier to modulator and modulator valve it's self too, they can develop leaks too!

 

At the fitting that the trans vac. line splits off the booster line disconnect it and take a fine piece of steel wire and clean out the nipple. I've seen the hole clogged on quite a few of these. Its a orificed fitting and gets blocked easily.