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This week I drove a 1991 300SE and then a 1990 300SEL. Both of them had about 100K miles. It seemed to me the transmissions shifted rather harsh, but I have had the impression that is rather normal for a Mercedes. Then today I drove a 1990 420SEL with 134K miles. It shifted noticeably smoother. This makes me think the harder shifting ones were not normal.

Is the hard shifting a known problem? If so, what does it take to resolve the problem?

-Jim

adler

The quality of shift depends on 3 crital parameters to get a smooth barely perceptible shift ,as i get in my 300se
Check the following items in same order to get a smooth shift.

correct Dexron oil and a/t filter
Transmisson vaccum modulater; leaky most need replacement, minor cost
linkage adjustment at the engine .tightening the adjuster will change the shift points,overtighteniing will result in hard shifts

adler

Old leaky Vaccum modulator will cause hard shifts .
it has a vaccum pipe from transmission to intake manifold connecter at cylinder #6

JohnLane

That transmission predated electronic controls.... all hydraulics with a vacuum modulator that decides when shifts happen.

Six cylinder powered cars will shift more abruptly then V-8 powered cars due to V-8s having more power. There is no power interruption to smooth shifts like in modern boxes.