Binding brakes
 

Had my first drive today (see separeate post), and it was stopping ok-ish under normal braking. However after trying some heavy braking, the rears have bound on - not completely locked, but substantially - enough to make it stall without lots of revs when pulling off.

The rears are BMW E34 disc brakes with separate internal drum handbrake.

Umm, help?

Left it overnight, and the brakes have released. Hmm, confused.

what we talking here is it the disc locking or the drum bit (you using foot or hand brake) and does it release if you reverse just a little tiny bit?

Hi Sam

Giving your rear brake problem some thought.

Are you using the used calipers from the donor car & have you changed the pads n discs ?

The sympom you describe is consitent with a partialy siezed caliper piston, this will bind badly when things start to heat up, releasing again when the caliper cools down again.

In my personal experience, older calipers that have been run for a long time with low friction pad material ( Or have been laid up for a long time ) are often a problem when new pads are fitted.

Moisture can & will find it's way past the pistons outer dust seal, this creates a layer of rust or crud on the surface of the piston.
Fine whilst it is still running on the same pads but the moment the piston is pushed back in to allow fitment of the new thicker pads, the crusty surface of the piston gets pushed past the calipers inner seal & tends to bind ( Getting worse with harsh braking )

If this issue persists, perhaps you should consider a new caliper seal kit, personaly, I would inspect the pistons condition first, if damaged by rust it would probably be almost as cheap to buy refurb calipers .

I hope this make some sense.

It`s likely to be as simple as pedal adjustment, just a tiny bit of pressure on the pedal will cause this. Make sure you have some free play on the pedal as even the weight of the pedal will cause it to bind when the brakes get warm, even stoplight switch adjustment will cause it too. Back off the pushrod and see if it cures it.

Dennis.

It's a disc locking up, and no, doesn't release if you reverse. :)

Yes Ronnie I'm using the donor's calipers with new standard pads. The donor drove and stopped well with them, and they had been fitted new at MOT just over a year before I got my hands on it, so I didn't feel a need to refurb them. However, it's was 3 years since they were last used on a car, before I used them on Saturday, so your explanation does make lots of sense.

I'm going to price up a recon set of calipers.

Thanks Dennis, I'll have a look at it, i need to modify the pedal slightly anyway to make it easier to find with my foot.

next logical step is to check if you have pressure held in the line(open bleed nipple and see if it releases) or its mechanical

I have an adjustable bias valve in the line that runs down the tunnel to the rears, i was wondering if it may be restricting fluid flow back to the master cylinder and holding the brakes on - the test you suggested would help discover if this is the case. I'm going to spend some time on the car this evening, will look at the brakes then.