I just had a new problem develop with my coupe. I am getting a loud clunk back at the rear differential area when transmission upshifts from 3 to 4. Clunk actually sounds like it is coming from the trunk area. It is very pronounced on a light throttle upshift - but if I accelerate under heavy throttle I don't hear the clunk when it upshifts from 3 to 4. The upshifts also seems a little harsher than they have been in the past. I'm suspecting it might be related to a vacuum leak or vacuum modulator problem ? Other than the clunk - transmission seems to be fine - no slipping or other noises. Any idea of what cause might be??

I have a simliar problem...will watch for solutions

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Daily Driver: 02 E430 4MATIC
In the family: '03 E500 // '04 ML500 // 64 220SE

Check those flex discs.

Are you saying you feel a Clunk, ONLY on a 3rd to 4th up shift, how about the other shifts,
are all the shifts harsh.

I have a 1993 300E with the same problem. 92,000 miles. The problem exhibits itself mainly for the first 30 minutes or so. After the car warms up it is less noticeable. It doesn't happen with shift point over 2500 - 3000 rpm. Just on lower rpm shifts. All other shifts are very smooth at any rpm. I've also noticed moving my car around in my driveway that it can clunk when moving from drive to reverse or vice vesa. Don't know if these issues are related.

Problem Solved!! The plastic vacuum line from intake manifold to transmission vacuum modulator was the culprit. Somehow it must have been exposed to a hot manifold or something and it melted closed in about the center of it's length - blocking the vacuum from being able to get to the modulator valve. 4 feet of new vacuum hose about 1 hour labor fixed the problem - no more clanks on upshifts.

Thanks to everyone who responded

May want to check the bushings on the rear end(The place where the rear pumpkin is bolted to the car) as these will collapse and give you the clunking sound you are referring .
Chris

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94 E320 with:
18" ///AMG Monoblock II's,AMG Gen II front bumper, H&R spings,500E sway bar, Bilstein sports, Eisemann Exhst, K&N,E500 Headlamps, Crystal Clear Corners, Avantgard Grill ...and more stuff to come! oh yeah 241k miles!!


My Car WOO HOO...... Now SOLD
New car.... 2001 Jaguar XJR!!!!

I concur with BadBenz, as this is the case in my car. One of the rubber diff mounts is worn out, and it sags a little. Every once in a while during a shift it bangs pretty good. Not every time, just a few.