denysserg

Hello,
When I press brake pedal I hear weird sound. It is not creaky. I have attached sound file (it is clean on my phone but on my computer I need to increase equalizers to hear it). The sound is kind of clunky. It happens on low speeds like 10 mph. Also it does not occur every time, but quite often (like every third time I slow down). What can it be?

https://drive.google.com/file/d/10xO...ew?usp=sharing

SLcharge

To me it sounds like loose lug bolts, but that can't be.

It is more likely one or both front wheel hub bearings that have either play or are damaged.
Lift up the front of the car, grab the wheel, and try to move it, by pushing in at the top and pull out at the bottom. There should be no play or movement at all.
Also try rotate it. It should rotate free and without noise from the bearings.

denysserg

Thanks for your reply. I have recently experienced loose lug bolts on other car and this is definitely not it. Can it be from brake pad wear? Do you know if it possible to check brake pads wear without removing a wheel? If not possible than I will follow your instructions.

SLcharge

Worn down brake pads sound somewhat different. It's constant grinding noise, when you brake. Metal to metal.

KEY08

Maybe you lost a pad retainer clip on that caliper and the pads are moving about. Check your pads and backing plates, etc. for movement.

denysserg

There is no movement of the wheel. But there is some sound when I rotate it. I found that the rotors inboard edge have fresh metallic shaving. I have attached some pics for more details.

I was not able to find any movement. But rotors inboard edge is slightly damaged.

SLcharge

I don't know why you don't hear that, at every speed, but your inner pads seems totally worn down to the metal. It is not only your edge that is worn, it's the whole surface that probably is ruined. Your calipers are of the "sliding type" with one sided piston. That means that during braking, as the pads wear down, the caliper must slide inwards. In your case, the caliper is probably stuck in dirt, and can't slide anymore, therefore only the inner pad is worn, and have to take the full brake load. You can also see that the thickness of the material, on the rotor, differ from side to side, that indicates that is has going on for some time already. There is also visual metal dust from the metal to metal contact.

I believe that you have to invest in a new set of rotors, and pads, plus you have to make the caliper move again.

This is a common failure with those calipers, and happens only because MB wanna save some money.

Arrie

+1.

Absolutely the correct diagnosis!

denysserg

I would change brake pads by myself but rotors sounds complicated. Have already left the car in mechanical shop. They told me that front rotors/pads/sensors should be replaced. So you are completely right. Thank you for all your help!

KEY08

Thank you for those photos. As said, brakes are toast

Arrie

And the root cause is the stuck caliper movement. Based on the pictures the outside pad is only half worn so this needs to be addressed as if not it will happen again.

Also, if there was extra long wired wear sensor it would be better to install on the inside pad where most of the wear is. Or did this car not have it? Or is this the side that does not have the sensor?

KEY08

The pad wear sensor is only in the right rear Outside brake pad and right front Outside pad. Only 2 on the car. The inside pad wearing quicker than the outside pad is a common situation with Mercedes vehicles. It is important to always inspect those inside pads by removing the wheel when you anticipate the brakes are due for replacement.