caliper brakes

[quiet330]

My front brakes on my 92 325 are pulling to one side upon release of the brake pedal. I suspect it is because I have a sticky piston in one of the calipers. My question is after the brake pedal is released and the pressure is reduced in the brake lines, do the brake pads continue to rub lightly against the rotors or do they move farther away? If they move away from the rotors what causes the piston to withdraw any farther than just to release the brake from the rotor?

[Manolito]

Depends on the design of the caliper. There is a rubber O-ring seal that sits in a groove in the caliper. That seal is square in profile, hence the name "square seal". The piston slides through that seal as it comes out of the caliper, pressing on the pads.

In some brakes, like the Toyota Starlet I used to own, the square seals in the caliper are thick enough that the action of returning to their original shape pulls the piston back far enough that the pads completely clear the rotors. The wheels spin freely if you jack up the car.

On most cars, the e36 being one of them, the pads rub on the rotors until the car gets up to 20-30 mph. At that point, there is a boundary layer of air traveling around with the rotor. The pad 'flies' on that boundary layer of air, a few thousandths of an inch off the rotor. Thinking of it another (less rigorous) way, the air forms a layer of lubricant, like the oil in your main bearings.

If one side drags harder than the other when the brakes are not applied, the problem is usually rust in a caliper. It can be a bent or crushed brake line, or a rubber brake line that is disintegrating inside and blocking fluid flow, but that is rare.

Rebuilding calipers is becoming a lost art. I don't know why. It is messy, but not terribly difficult. I used to do it a lot. People just buy 'new' (rebuilt) calipers these days rather than rebuilding them.

If you find rust in a caliper, someone has not been changing the brake fluid every two-three years as they should. That probably means that they have not been replacing the engine coolant every two-three years either, so you may have rust in other places.

[mikecgolf]

I hear a light schoosing sound coming from my front end at lower speeds. Is this possible caused by the caliper being in contact with the disc as it is is designed to do?

This sound leaves when I push in the clutch and returns when I let it out. Is this possible for the brake caliper contact noise?

1996 328ic M52.

[Manolito]

A sound that changes when you push in the clutch is not coming from the front brakes. There is no relationship at all between the clutch and the front brakes, other than they are attached to the same car.

A sound that changes when you press on the clutch is normally related to the throwout bearing in the clutch. Could be a failing bearing, or could be rust or dirt on the transmission input shaft or transmission housing neck.