When I bought the car last December they had just replaced the front rotors and pads, and they were pretty uneven which I attributed to improper breaking in, but they haven't improved. The biggest problem is that get really hot on long trips. Hot enough that the plastic Mercedes valve caps partially melted.

My initial thought was that the caliper pistons were sticking, so a couple of days ago I took the brake pads out on the right front to see how the pistons moved and both of them moved smoothly, so I am not so sure any more.

I get a vibration from the brakes but not a sheering wheel shudder, so now I am wondering whether the booster has a problem. There is also a fairly sharp transition between light and heavy braking.

I have never run into this before and will appreciate any thoughts or suggestions before beginning to replace parts.

Thanks/Anker

 

I agree with Plutoe - bad calipers. If anything (booster or ESP system) were erroneously applying the bakes, you;d get an ESP error.