fireboat

I have an issue that I haven't been able to resolve. I have a 2011 manual transmission C300 that I have had since new. It has been exceptionally reliable but now the rear brakes are dragging/sticking intermittently. When the dragging/sticking occurs, I can feel the car slow down as if lightly applying the brakes when I push the clutch in and coast. Sometimes the dragging is more severe than other times. Generally, if I quickly tap the brakes the issue goes away for awhile.

I have jacked the car up and it seems to be only the rear wheels affected. If I crack one of the rear bleeder screws, the brakes immediately loosen up. Even though this tells me it is not the calipers, I replaced both rears with Ate calipers and new pads and new rotors. I also replaced the rubber brake hoses. As I suspected, this did not resolve the issue. I flushed the brake system with no change. There are no warning lights or fault codes. The parking brakes look fine with no undue wear and the cable and actuator seem to function normally. However, the rotors and brake pads are showing premature wear on the rear wheels. The issue appears to be confined to rear hydraulic brakes.

I suppose the master cylinder could be the culprit and I will replace it next. It doesn't seem like that the ABS or traction control would be the problem? I took the car to the local MB dealer and they charged me $800 (they replaced the accelerator pedal) but did not fix the problem. It is an intermittent problem so I know it can be hard for them to diagnose even though they drove it over 25 miles. Anyway, has anyone else experienced a similar problem? Or have an idea as to the cause? Thanks

Adi-Benz

I would check for a sticky parking brake for the rear.

superangrypenguin

This. Try yanking on the parking brake release a ton of times and see if that causes it to go away. try then applying max parking brake, and do the former again. Try this again and again, and I bet you 1/5 times you won't hear anything squeaking.

I had to replace my parking brake kit because of this issue. It wasn't bad. I think it was $300 all in...

The other option the OP can do is to wear some nitrile gloves, and stick his or her hands behind the rim, and behind the rotor. There is a metal plate in the back (circular). try pulling it towards you, and try this on both sides. This may cause the issue to go away, and if so, it is indeed the parking brake "stickiness" problem which is resolvable by way of replacing the entire kit.

Sorry, English is bad today. Long day.

Whitebuffalo

I know this is an ancient thread, but I’m having the exact scenario. Manual Trans 2011 c300. Back brakes only and it’s hydraulic so not parking brake related. I’m thinking maybe the yaw sensor but wanted to see if by some slim chance OP is still here and what the resolution was

JettaRed

iTrader: (1)

Have you connected and scanned with a Mercedes-specific scan tool? You may be able to view live data to see if the brake system is functioning correctly.

Whitebuffalo

I have a icarsoft mb v3 and have a historical code for no can bus comms to yaw sensor but real time data all shows normal for wheel sensors etc. the issue is highly intermittent so I haven’t been able to see what it shows when it actually happens. It almost feels like the hill assist fails to release. I replaced the hard lines all the way from the abs to the wheels and verified the pressure isn’t being trapped at the soft lines. It acts like a electronic issue more than a physical one unless it’s the abs pump internals or master cylinder

TimC300

I would think if it were an electrical issue the abs light would turn on, even just when it is happening. Im just speculating.

i know you say you verified the pressure but I would double check the lines and hoses and fittings. A few threads I just skimmed over the cause turned out to be the brake hose.

Whitebuffalo

Agreed about the light. It’s the damndest thing.

the way I verified its not soft lines was I got it in a brake hanging state and cracked the line where the hard line meets the soft line and pressure released and brakes released (granted not a 100% test but the caliper did release so seemingly they’re good).

dumb questions since I just got a hold of the icarsoft for anyone that is savvy with it:

my wheel speed sensors do not go to zero. They show a very low number (I don’t recall exact value) and seem to increase in harmony with speed but don’t go to zero.

does anyone know what the brake pressure reading should be without brakes applied? Mine shows .9 bar without brakes applied.

same thing for rotational speed: mine shows 10.1 and I’m not moving

longitude accel shows .10 and lateral shows -.15, although granted I was on a slight incline.

does anyone have baseline numbers I can compare to?

JettaRed

iTrader: (1)

Where (what module) are you reading your brake pressures in iCarsoft?

JettaRed

iTrader: (1)

According to XENTRY, brake pressure when NOT actuated needs to be between -87.02 psi and 87.02 psi. Not much help, I guess.

Wheel speed of < 2 mph (or 3 km/h) is considered stationary. If yours is showing 10.1, something is wrong.

JettaRed

iTrader: (1)

Well, I could be the ABS (ESP) as there is a pressure regulator (A7/3) that requires calibration of the Yaw rate sensor if certain components are replaced. You would replace a component if it were to fail. Maybe the problem is with one of those items.

Whitebuffalo

is have to look but I believe under diagnostics and then esc iirc. I’d have to look again, I’m still getting familiar w it

Whitebuffalo

the 10.1 was rotational speed. I have no idea wtf that is measuring. Wheel speed I don’t recall exact reading but it jives with <2 iirc so that makes sense.

brake is showing .9 bar when stationary so that tracks

JettaRed

iTrader: (1)

I would think the brakes should have zero pressure when not activated.

Each wheel has a speed sensor. If one or both of the rear wheels has a defective speed sensor, that could make the ABS malfunction also. If you are looking in the ESP module for wheel speed, then 10.1 could be mph or km/h. Regardless, 10.1 in either unit of measurement is too large when stationary.

Whitebuffalo

the yaw sensor doesn’t seem to be Caput entirely but maybe it’s intermittently throwing a rogue signal or dropping off? I hate to start slinging parts at it bc that gets pricey but I have to make a move I guess pretty quick because I’ve been scratching my head and sitting idle for a couple weeks now and not really coming up with anything concrete. Do you think the yaw sensor throwing a rogue signal or dropping communications would cause just the rear
brakes to fail to release? I’m seeing some internet chatter of people claiming the brakes engaged on their own due to it. In my case, they’re not engaging randomly on their own, but they’re failing to release when applied (at a stop seemingly)

JettaRed

iTrader: (1)

I'm not really sure what's going on. Were you able to see the reported wheel speed for each wheel? The way ABS/ESP normally works is if one or two wheels are faster than the others, the car thinks the faster wheel has lost traction and will apply the brakes to that wheel to slow or stop it from spinning. You can turn ESP off and try driving that way (carefully) to see if the problem recurs. If it does not, we have narrowed it down to what is probably causing the problem. Usually, however, there is a separate code for a failed wheel speed sensor. But, it could also be the tone ring on the wheel hub.

I can't go forward with Actuation of the A7/3 module when using the simulation mode, but a condition for calibrating the Yaw rate sensor is replacement of A7/3. That tells me that those components can fail. It blows me away that the dealer charged you $800 for not fixing the problem. Were they able to detect a fault in the accelerator pedal that justified replacing it, or were they also throwing parts at the problem. On a whim, you may consider the brake light switch could be causing the problem. It's an inexpensive part and easy enough to replace yourself. It fits next to the brake pedal and is depressed when you step on the brakes. Who knows how all of these signals interact?

alynch

A little different tack. Could it be the piston intermittently sticking in the caliper? So, rather than the brake intermittently being applied, the caliper is not releasing after braking. A mechanical rather than control/electrical issue?

Demvang

I agree with JettaRed regarding the wheel speed sensors. If you unscrew one of them, car will apply brake itself, less 10Mph because that was the problem for me.

JettaRed

iTrader: (1)

I think the OP said that loosening the bleed valve allowed the piston to retract without additional pressure. Maybe I misread that. If that were the case, it seems that pressure is being maintained even when the brake is not being applied. That's why I think the A7/3 module could be the culprit.

Whitebuffalo

I wasn’t the guy who spent the $800, I’m just having exact same scenario as him. EDITED TO ADD: that’s not meant as me being a smart ***. Just clarifying bc I know I dug up an ancient thread and everyone hates that for this exact reason.

Can you tell me what a7/3 is? From what I was reading elsewhere the yaw sensor could be replaced without any fanfare aside from the getting to it

Whitebuffalo

I thought about that. When the problem first presented it was on old pads that were about spent. I put new ones on and it still happened. Not that that would rule out the caliper piston, just my line of thinking was that piston is in a completely different spot now that when it started. Still a possibility, but I had seen either OP or possibly another person with same problem who had tried new calipers to no avail.

if it was calipers though, would it have instantly released when I opened the bleed screw? (I’m asking- that’s not rhetorical)

Whitebuffalo

correct: instant release with the bleed screw

JettaRed

iTrader: (1)

LOL! Are you sure you didn't pay $800 for a $100 gas pedal?

JettaRed

iTrader: (1)

Seems the A7/3 is called different things, but it looks like an ABS controller. I'll see if XENTRY has test procedures for it.

JettaRed

iTrader: (1)

I'll try to find more about it.