Harsh gear shifts under light throttle

[Dymian82]

Hi everyone,

I'm looking for some advice regarding my 1992 Mercedes-Benz 500E

When driving gently with light throttle, the gear shifts feel quite harsh and noticeable. However, when driving more aggressively (with more throttle), the shifts are much smoother and barely noticeable.

The ATF and filter have been replaced, but it didn’t make any difference.

I've heard this could be caused by:

• a faulty or incorrectly adjusted vacuum modulator,
• a disconnected or leaking vacuum line,
• incorrect Bowden cable (kickdown) adjustment.

Has anyone experienced something similar or could suggest where to start with diagnostics?

Thanks in advance for any help!

 

[gsxr]

I've heard this could be caused by:

• a faulty or incorrectly adjusted vacuum modulator,
• a disconnected or leaking vacuum line,
• incorrect Bowden cable (kickdown) adjustment.

Shift firmness is controlled by the vacuum modulator. This is where to start looking.

Shift RPM's are controlled by the Bowden cable adjustment. This WILL NOT cause harsh shifts.

Has anyone experienced something similar or could suggest where to start with diagnostics?

Verify the vacuum line from intake manifold to modulator is intact at both ends. Also make sure the cap is installed on the vac modulator (early type has rubber cap, late has plastic cap). You can connect a vacuum gauge with a "T" fitting at the modulator and go for a test drive, observing the vacuum... should be high vacuum at light throttle, zero vacuum at full throttle. If all that checks out ok, you could try adjusting the modulator softer (in case a previous owner misadjusted it), or just replace with new.