Weird brake problem
 

220D from 1973 (114?)

Howdy,

A friend took my car for the technical check, it failed on a sticking back brake. He's cleaned everything up and backed off the handbrake a little.

Everything fine till........

He tightens the wheel back up, then it starts to stick again.

I haven't seen it yet, but he asked me on the phone if I might have longer bolts on that side for some reason.

My only thought is that it may be a different rim, I bought a tyre from a scrapyard on a BMW rim once.

Any thoughts or comments on this one greatly appreciated.

My WAG is that you have a sticking inside piston on that wheel and possibly a warped rotor. When the wheel lugs are tightened, it is forcing the rotor against the pad. The lugs are what hold the disc on tight against the hub.

Thanks ctaylor, that would explain it, dammit.

I guess a sticking piston has caused the rotor to warp, looks like a trip to the junkyard for some bits and pieces.

Should also consider replacing the rubber hoses on the back calipers, as these often swell shut. That then causes the brake fluid to not back flow when the brakes are released and is a contributor to piston seize. They should be fairly inexpensive.

So I got the chance to take a look at it in the weekend.

I eliminated the disk brake pretty quickly as being the cause of the problem, i.e. removed the caliper and tested.

Sure enough if i tightened the wheel up, it would stick, and you could hear rubbing.

There is a sort of ridge that runs around the back plate and slots into a groove running around the drum. That shows signs of scratching so I got the sandpaper out and removed the rust.

I think that was the cause of the scratching noise.

Brake still stuck on, even after backing it off totally.

My friend..... "See that lug there, it was in the wrong hole".

(There is a guide lug which means that the drum can only be put on in two positions, one more correct than the other)

Me....... "let's try it how it was".

Problem solved, although not in the most scientific way it has to be said.

My synopsis? I must have done something wierd to the handbrake by having the drum on incorrectly, and for some reason the car has grown to like it that way.

"Wierd Brake Problem" indeed.