brakes again

OK new calipers, new brake pads, new brake hoses and now the brakes are dragging. should the master cylinder be changed?

1982 380 SEC

benzat

[JimSmith]

benzat,

What exactly do you mean when you say the brakes are "dragging" after all that work?

Can you hear them touching slightly? Or do they lock the wheels up? Does it affect all the brakes or one? If you have already described all this in a previous thread, I am sorry to ask you to do it again, but a little more precise description of "dragging" would help understand the problem. By design the pads are supposed to essentially be touching but without any pressure. They do not "retract" any real distance into the caliper when you take your foot off the brake, so if you are hearing some rubbing, but you can turn the wheel by hand, it is probably ok. Jim

well I can tell you they touch so much I can smell the front brake pads burning. I think its both but not sure. Im taking the car in for this problem soon I got a new master cylinder and I also have to have the motor mounts and the engine shocks put in...OH what the heck this car has an attitude for my paycheck thats why I call it benz with an attitude. lets just say this is one of the smaller problems Ive had with the car.

benzat

1982 380 SEC

[JimSmith]

I have seen this problem reported a number of times in this and the Diesel forum, so you are not alone. I have tried to explain what is supposed to happen when the pressure on the back of the pistons in the brake calipers is taken away by the operator moving his foot off the brake pedal. Unless the master cylinder or brake pedal springs have failed so that the residual pressure on the back of the piston is maintained significantly hgher than the static head of the elevation difference between the brake fluid reservoir and the caliper, this is a caliper problem. You can check the residual pressure, or the brake pedal return motion, to see if there is a problem with those features. Each of those options would affect alll the brakes equally. If one is hanging up it is definitely the caliper.

Not all rebuilt parts are necessarily correct. I have had an alternator, sold as a rebuilt unit from the dealer, act like it was working at idle but fail to charge the battery. Of course I assumed the alternator was not the problem, and went nuts trying to find shorts and the like.

Anyway, the piston seal ring in the caliper is the ONLY thing that pushes the pad back away from the disc when you release the pedal pressure, assuming the pedal returns all the way to its rest position and the springs in the master cylinder push the pistons in there back to their rest positions. The failure of one of the master cylinder springs would be unusual in my experience. A mechanical hangup on the linkage from the pedal seems more likely, which could leave the master cylinder kind of preloaded a little.

Sorry I can't be of much more help. Jim