adjusting vacuam modulator - PeachParts Mercedes-Benz Forum

420benz · #1 07-09-2002, 10:41 PM

Trans is shifting hard.I turned the T bar on the modulator counter clockwise 4 slots.It got a little better but not much.How much can i turn this T bar? When shifting from N to D it is harsh from D to 2nd & 3rd is not as harsh.Fluid & filter was changed 3000 mi. ago.

#2 07-10-2002, 08:48 AM

Im not an expert with benz's, but i had the same problem with my 500 sec, also a slightly rough idle. Everything looked fine, tryed adjusting the modulator, but did not help very much, after a few hours of fiddling with this thing (and a few choice words), it turned out to be a small, tiny slit in the vacuum tube, i only noticed the slit after taking the hose off and throughly checking it for about 30 minutes! It was so small, i could hardly see it, but it was enough to lose vacuum. I replaced the tube and the trans shifted perfectly, nice and smooth from park or neutral into drive or reverse. Like I said, im not an expert, but that was my experience with the trans modulator!!

Good Luck!

stevebfl · #3 07-10-2002, 10:47 AM

Go farther! It takes a full turn to get much results.

Be sure the trans is shifting early enough (control pressure cable adjustment).

greenacres2 · #4 07-10-2002, 12:44 PM

Steve,
Does the modulator pressure affect the shift from neutral into drive? I was under the impression that it only impacted the shifting between the forward gears (i.e. 2 to 3 to 4 and back down). Thanks for your continued education!

stevebfl · #5 07-10-2002, 02:37 PM

Modulator pressure controls shift pressure. Shift pressure can be different for forawrd and reverse gearing but each value will change up and down with modulator pressure.

#6 07-20-2002, 03:07 PM

The transmission on my '89 300se uses ATF although there are never any leaks. If the modulator valve fails can the ATF be sucked into the engine thorough the vacuum hose?

stevebfl · #7 07-20-2002, 03:19 PM

Yes.