Posted on C207 board before but issue is still there.July 7th, Front brake pads and rotors replaced, Rear brake pads replaced (not rotors), genuine parts from MBZ dealer. Engine mounts replaced as well as transmission mount. Brake fluid was not changed, no bleeding either.

Usually the first drive in the morning after the car has been in the garage overnight. I think also if the car has been parked for a while, wheels have cooled down?

Pressed on the brake firmly gently all the way down like when shifting gear, starts the engine, puts the gear in reverse, backing out of the garage is a down slope, releasing the brake and pressing it firmly (while still in the driveway downslope) and repeating this often results in a loud noise as if the brake calipers compressed (grabbing the rotors?) and then decompressed (releasing the rotors?). Sometimes it can be very loud, like a machine compressing and decompressing with insufficient lubrication (hard to describe.)

As the car backing into the street, it is backing upslope as the wheels turn so the front can face downward, then steps on the brake firmly and all the way down again to change gear to Drive forward,

NOW RELEASING THE BRAKE SO THE CAR CAN GO FORWARD, IT USUALLY HESITATES FOR HALF A SECOND AND IT CREATES THIS LOUD NOISE AGAIN LIKE THE HYDRAULIC COMPRESSING AND DECOMPRESSING, SOMETIMES VERY LOUD. I think the sound seems to be from the front, from below engine compartment, its kinds of hard to pinpoint but I think it is associated with compressing and decompressing the brakes (step on brake then let go.)

Perhaps this is like the car is moving forward from a HOLD function or a HILL START ASSIST FUNCTION and it creates this loud noise.

The noise subsides after driving a while but sometimes still does when in the same pattern (reverse downslope braking.) Sometimes it happens on level street as well but to a much lesser degree and not very loud noise.

No freezing as wheels stop when put on brake and can move freely when brake pedal not applied, mechanic checked while I was there.

 

I think this is PARKING BRAKE issue.

Remember reading about it in other sections for sedans...
search it

 

Thanks, but I think parking brake is in the rear? The loud noise is from the front though.
I will try searching for the thread you mentioned.

 

did not notice where you said from front.
Locating exterior noises while inside with windows up inside can be PIA.
DO you feel anything in brake pedal or steering wheel or with your butt in the seat?

simple first check would be front suspension components for bolt proper torquing, worn joints and/or bushings.

But for brakes:
I would Remove wheel and inspect all 4 corners.
Check calipers move properly side to side.
Check pads move freely side to side
Check pad holder thingy clips are proper etc.
Double check hardware for proper torque

4 Matic? check front drivetrain.

 

Thanks again, I did try google again for brake noise in reverse and found some of these (I copied the texts)You mentioned recently replacing the brake components. It sounds exactly like it’s your pads just adjusting to the new direction you’re traveling in. Some very minor slack in the area where the pads are hanging/mounted to the caliper. If I am correct, then you have nothing to worry about as it happens to many cars after new pads have been installed. My Toyota, VW and my MB all do this as all have received new OE pads and rotors over the past year.

Annoying a little, yes. But not a major problem.



PS, not sure where you live, but cold air will exaggerate this a little more as the metal contracts. In hot/humid summer, likely not an issue.



The solution is likely in the brackets on the pads and not the pads or rotors themselves. I can’t recall at the moment what the brackets are like, but may be a situation where one or two just need a little bend on a tab to make them a little more snug in the housing.
Your brakes may look like this. Inner pad has a clip that fits into the piston, outer pad has a spring clip to provide tension.

The caliper mounting brackets themselves have some stainless steel insert clips as well that fit into the rail where the pad ears sit - do your mounting brackets have all new clips? Those clips are designed to cushion the pads as they want to move around.
Another source of noise (besides loose caliper mount bracket bolts that I doubt you have) are the slide pins. If they are very worn, the entire caliper can rock back and forth depending on wheel direction.

Had this , right after installing new rotors and pads in front.

noticed next morning when i started backing out from garage , i heard like a thump/pop/knock. I could pinpoint it was the driver side. Found time to check and lubricate everything and also bent the metal brackets.

and the sound was gone. So im sure in my case it was the brackets. When i had them off i bent them in a little.

end of story

I am not sure which of the above fits my situation, I do remember the mechanic said that the new pads are not exactly fit and there is a little play when hung?
I do not know if brakes readjust when the direction is reversed (from forward to backward and vice versa), if that is the case then could it be the pads are adjusting to the directions and causing such loud noise or whatever.
At this point, I was hoping to get a mechanic to disassemble the whole thing and reassemble them again and see if that will resolve the issue. Need to find a mechanic that has some experience dealing with this type of issue. The two mechanics that have looked at them claimed they did not see any issue. Its a bit frustrating because mechanics are quite busy and rather deal with other jobs than trying to trouble shoot a problem.

 

first time you install new pads and then pump pedal first time to stop... the caliper pistons extend and take up all the slack and then back out a tiny but to allow rotor to spin against with least friction from pads.

would make noise just that one time.

you got something else and need to take wheel off and look and feel and see what moves that shouldn't.
Check for loose hardware