Problem...Breaks Hum and get Hot. - PeachParts Mercedes-Benz Forum

bart · #1 03-07-2005, 07:17 PM

Ok I have a new problem.....

I just changed the back right rear rotor out, and put in new break pads on both rear tires......Everything seems almost back to normal except that the breaks with the new rotor hum at around 40 MPH and only after they get a little hot......Also the whole rim and rotor is getting much hotter than the other three wheels. You can touch the rims with your bare hand, but only for a few seconds. I also noticed a burning break fluid smell at an intersection which cant be good Im sure.

Anybody have any clue as to what this problem might be? I noticed that if I apply the breaks even just a little bit the humming stops.

Are the breaks riding the rotor possibly? Or worse yet, could the bearings be dry and creating extra friction?

This same wheel has been giving me many problem since I got this vehicle, a 1982 380SEL.

Any answers would be very helpful.

Thanks,

Erik

psfred · #2 03-07-2005, 08:32 PM

Erik:

Two things:

One, it's VERY STRONGLY advised to replace brake parts in axle sets (that is, both rear rotors and both sets of pads) to avoid having one side work and the other not. In your case, I suspect only one rotor is bad, and that is why you only did one.

You have a badly stuck caliper on that side, and if you had mud on there, you have problems on the other side as well.

You should either rebuild the caliper, or if you are not comfortable with that, I would avise replacing it. Rebuilt calipers aren't expensive for that car. I would ALSO replace the one on the other side, and bleed again (you've already flushed the brake fluid out!).

What has happened, most likely, is that someone ran the rotors too thin on the rear and didn't change the pads soon enough. This allows the pads to hit the anti-rattle spring, and that causes them to tilt since the top cannot move in any further. This cocks the pistons in the bores, and they stick there, causing the pads to drag badly, overheating the calipers and destroying the rubber seals. Water and dirt get in, and they REALLY stick!

I'll bet the pistons were pretty hard to push back into the caliper when you change the pads, right?

Get new (rebuilt, really) calipers for the rear, and plan on new ones on the front next pad change, too -- you'll be astonished by the difference!

The noise and heat are a result of the piston failing to retract on the seal.

Peter

bart · #3 03-07-2005, 09:31 PM

Yea Peter, you are right....The piston was next to almost impossible to push back in when I changed the rear pads on that side, even with a large C clamp, I even had to use a pair of grip pliers on the c clamp to get more leverage to turn the screw on it.

Im not sure what you mean about the mud on the other side unless you mean from what I put in my other post about my break problems. (When I took apart the calipers on the left side there was silty mud like stuff gooped up in the rubber seal where the break fluid flows and the calipers fit together. I was told this was water, rust and other contams)

Well, obviously my breaks system is in need of a major overhaul, plus the car is old and I am sure the breaks have probably never been rebuilt since it rolled off the factory lot. I guess I will have to bite the bullet and get to work on rebuilding the calipers. Sounds like its gonna cost quite a bit, four new rotors, and four rebuilt calipers, at least I can probably do the rebuild myself. I havent checked em but I think the front pads are about to go also.

Thanks for the advice Peter.......Now then, where to get rebuild kits....Didnt someone on another post on here say you can get em from the dealership?

Thanks,

Erik

manny · #4 03-07-2005, 10:35 PM

Like this ?
http://img.eautopartscatalog.com/live/N105040226ATE.JPG

Click FastLane, Brakes, Caliper repair kit.

psfred · #5 03-09-2005, 06:23 PM

Details have been posted many times. Expect to replace the one caliper with the badly stuck piston as either the bore or the piston (or both) have probably been scored badly by forcing it back in.

My advise, normally, is that if they are that hard to move DON'T force them in, stop and get the rebuild kit since you are going to have to rebuild them anyway, and it's much easier to get the piston out as it.

DO NOT use compressed air to get that piston out for the rebuild, if it does come out, it will blow out at about 100 mph and could easily kill you if it hits you. Clamp the other piston in and pump it out with the brake pedal -- much safer, won't hurt anything.

Do not use abrasives on the bore below the piston seal (you will need to remove the corrosion above the seal, for sure) or at all on the piston -- the piston is chrome plated, and if you scratch the plating, it will both leak and probably peel the chrome off eventually. Make sure you get ALL the grit and dirt out of the bore, else the piston will stick again.

If there is corrosion in the bore below the seal, or on the chrome plating of the piston, get another caliper.

Peter