PeachParts Mercedes-Benz Forum - View Single Post

EricSilver · #7 11-16-2021, 04:28 PM

UPDATE

Existing transmission mount (15 months old) is still good, per my tech and Engine mounts are 5 months old, so these have been ruled out as causes.

Today, after replacing my worn-out (after only a year) Continental (crap) serpentine belt with a genuine Mercedes one, the vibration is significantly less but some still remains. I I believe it is being caused by the exhaust.

The vibration occurs mainly while stopped at traffic lights. It is essentially gone in Park and Neutral; and weakly present in Reverse.

Curiously, this pattern seems consistent with the secondary air pump cycling on and off (or high and low?). For example when arriving at red light there is a heavy-ish rumble that fades significantly about 3 seconds after coming to a complete stop. (With my E430, I could actually hear the air pump kick in when I came to a stop so I assume the behavior is the same in this car, with the pump adjusting the fuel/air mixture and causing downstream effects on combustion/exhaust output.)

Also, last week I noticed a metallic rattle on the first cold start of the day, precisely between 825-850 rpm. Moving above or below that narrow range stops it instantly. Looking around at the underside of the car I could feel the exhaust is a bit loose. Upon closer examination, I discovered the broken bracket/hangar assembly in the attached photo (rear, Driver side). Pushing lightly against the exhaust pipe in that area also instantly stops the aforesaid morning rattle, so it is clear the exhaust is oscillating enough to tap against one of its heat shields.

It therefore seems reasonable to conclude this same oscillation is transmitting the cabin vibration via the engine/transmission -- except when the transmission is disengaged in Neutral or Park.

Question: How involved, or not, would this fix be? I am assuming any muffler shop can do it.