Weird brake issue- '85 300D - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 02-27-2017, 08:34 PM

My niece was driving their extra car ('85 300D) home a while back. She pulled over because the car did not have enough power to climb the grade on Cajon Pass (3,500'). It seemed like the rear brakes were on. When she stopped, she noticed that the rear brakes were smoking. She had the car towed home. A couple days later, my brother drove the car and everything worked fine. A couple days after that, he drove it and noticed the pedal going to the floor and barely stopping. He had the car towed to my house yesterday. I noticed brake fluid leaking from both rear calipers, so I replaced them with a pair of good used ones. I also put on a pair of turned rotors as well as new pads. Now comes the weird part. I successfully bled the rear brakes, and moved to the front. When doing the passenger side, I noticed (heard) bubbles in the fluid reservoir. I was able to get all the air out of that side, and moved to the driver side. I noticed the same bubbles in the reservoir when pushing down on the brake pedal. After bleeding the brakes, I test drove the car. It seemed to stop just fine. I was able to skid the front tires, and I imagine that the rears will get better as the pads wear in. However, the bubbles still concern me. Could there be something amiss with the master that would have caused the rear brakes to lock up in the first place? I will probably just replace the master for good measure anyway. I just don't want this to happen again......Rich

kerry · #2 02-27-2017, 08:42 PM

I believe old brake hoses can sometimes cause calipers to stick.

ROLLGUY · #3 02-27-2017, 08:49 PM

Quote:

Originally Posted by kerry

I believe old brake hoses can sometimes cause calipers to stick.

I have heard of that too, but one would think that condition would still exist.

Diseasel300 · #4 02-27-2017, 09:48 PM

I won a lemon lawsuit against Ford Motor Company in the late 90s for a failed master cylinder causing exactly the same issues you describe above. They refused to acknowledge the issue or fix it, insisting on fixing other issues. Meanwhile, the brakes would continue to apply themselves and eventually stop the vehicle. I've never forgotten it, and I've never owned another Ford either. Bottom line - a MC problem CAN cause the brakes to hang up!

sixto · #5 02-27-2017, 10:41 PM

Maybe the master cylinder forward piston isn't retracting when you release the brake pedal.

Sixto
83 300SD
98 E320 wagon

Mxfrank · #6 02-28-2017, 12:05 AM

Bad master or swollen brake line, you have the two likely answers. Master maybe a bit more likely, since it releases by itself. One more possibility would be an air leak in the booster system, although this would affect the fronts also.