On my new 98 E300D I had to get some exhaust work done. Specifically, the entire section of pipe from the cat to the muffler was replaced. However, one thing I noticed is that there is a resonance at 900 rpm that was not there before. (The exhaust guy did not know the word "resonance," but he understood when I used the word "vibration." haha)

They are happy to do whatever they need to do to make it right, but claim that I probably need new engine mounts. Personally, I doubt that this is the case, but I will know for certain when my indie looks at the car next week.

Working on the assumption that the mounts are fine, how does one go about eliminating/dampening exhaust resonances and vibrations? The exhaust shop said they could install a flex pipe but that I shouldn't need it since that's not how the car was designed.

Thanks.

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 154k miles
06 E320 CDI "Rutherford", Black on Tan, 172k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 142k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

I would say that vibration resonance, as distinct from sound resonance, could be fixed by either a flex connection or a different stiffness of mount or perhaps a mass clamped to the pipe somewhere.

A noise resonance can only be fixed by changing the length or diameter of the pipe, basically. In industrial applications there are duct resonators and other tricks to dampen resonance.

Sometimes with a new muffler, the muffler will "break in" as whatever sound damping material inside (if any) settles in, etc.

Rgds,
Chris W.
'99 E300D, 407K

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Objects in closer are mirror than they appear.

It also makes me wonder what changed that accounts for the resonance. The material? How it's suspended? Where the bends in the pipe occur?

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 154k miles
06 E320 CDI "Rutherford", Black on Tan, 172k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 142k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

Well that was simple. Turns out that the heat shield was bent in such a way that it was touching the muffler....and vibrating at 900 rpm. Bent it out of the way, problem solved.

__________________
14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 154k miles
06 E320 CDI "Rutherford", Black on Tan, 172k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 142k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife