RobertwW63

I have a squealing issue with my ml350 that I cant seem to figure out. It runs, drives, and stops, like new. No braking, shifting, handling, or power issues. It only happens when I am accelerating. It doesn't make any noise if I am holding a constant speed. Doesn't matter if I am turning left or right. It doesn't make the noise if I am parked and stepping on the gas. It doesn't squeal right away if it has been sitting for a while but never takes very long to appear. Sometimes I have to accelerate hard to make it squeal, while other times it happens if I barely press down on the pedal. Speed does not affect the pitch, loudness, or frequency, of the squeal. It does not squeal in reverse. It seems to be coming from the front but I am not sure.

The squealing started after I replaced the pads and rotors but I am not convinced that this is the cause since it only happens while accelerating. The only reason I replaced the pads and rotors is due to 1 warped rotor that was pulsing while breaking. I am the type of vehicle owner that will replace all 4 even though only 1 is bad. I am meticulous about maintenance on my vehicles.
It is never taken off road, never used to haul heavy stuff, never driven hard.

I cant think of any more details off the top of my head. I tried using the search and could not find anything that was remotely close to the issue I am having. Thank you in advance.



04 ml350
143k miles
new pads and rotors all the way around (meyle)
new belt (gates)
new idler pulley (oem)
new tensioner pulley (oem)
fresh gear oil in front and rear (royal purple)
fresh transfer case fluid (royal purple)
fresh oil change (Mobil one)
Giovanna wheels (much lighter than stock wheels)

Maj. Dundee

Whichever wheel had the problem, you should check the backing plate as it might be bent in slightly towards the rotor. Or the caliper in not retracting enough.

RobertwW63

Thanks for the quick response. Checked the backing plates. They aren't touching. If it was a stuck caliper wouldn't it squeal all of the time except when braking? Mine only squeals on acceleration. I will check the calipers tomorrow.

Maj. Dundee

The squealing is probably present but not audible to you except at higher speed.

You must clean the areas on the caliper with a rigid wire brush where the brake pads fit into (red arrows).

After cleaning, apply a small amount of Copper Based Anti-Seize paste to those areas on the caliper.

RobertwW63

Speed doesn't affect the noise. It will squeal at any speed.

Took everything apart and cleaned it with a wire brush and applied copper anti seize. It is still squealing.

Any other ideas?

DrX

Check your engine mounts. Have they ever been replaced?

One of the things that happens only when you accelerate is the torque of the engine makes it rotate clockwise on its mounts. If the LH mount fails (which is subject to the most tension - the RH mount gets compressed), the left front corner of the engine will sit up. This could cause rubbing by a component that rotates at a constant speed compared to engine RPM or wheels. Like anything driven by the serp belt, including the fan, alternator or AC compressor.

Maj. Dundee

Does this mean the brake pedal?

"while other times it happens if I barely press down on the pedal."

RobertwW63

No. The gas pedal. It only happens when I am accelerating.

RobertwW63

Drx I will check the motor mounts today

RobertwW63

Motor mounts are solid. Checked my paperwork and they were replaced 4 years ago right before I bought it. I went ahead and checked them anyways and the was very little movement.

RobertwW63

Is there any chance it might be the front driveahaft or possibly the support bearing?

Maj. Dundee

Have you made any headway on your problem?