E36 Rear Brake Hot

[Chilly]

So my back left brake is giving me problems. Sequence of events:

1. Bought car a few months ago. Shortly after the brake started occasional squeal when backing up. Progressively worse, developed a groan. Groan would go away when I'd press brake going forward and would not return until the next time I'd back up. The noise in reverse would happen when my foot was not on the pedal while backing up.

2. First inspection showed missing anti-rattle clip on caliper. Got a new spring. I think I noticed a bit of a rut worn on the caliper carrier slide rails perhaps due to caliper being allowed to rock without the spring. Noise goes away. No problems for a while.

3. Some few weeks after installing the spring I get a new problem. Noise never comes back but now the brake gets very hot.


My thoughts on possible causes
- Maybe the pad hangs up on the groove in the caliper slide and pads aren't retracting fully.
- Maybe something is wrong with parking brake function. Have no idea what auto adjusters are like on this thing.
- Maybe the parking brake cable is jammed up.
- Maybe the caliper is hanging up.

Any ideas on this one? Tips for eliminating some possible root causes or isolating others?

Thanks,
Chilly

[Yurick]

Raise the car off the ground and hand-spin the troubled wheel to see if it hangs up. You will need to isolate the parking brake's shoes from the normal braking pads and then you will have a more clear direction to take.

[Jeron]

So the pad backing plate wore a groove in the slide rail? That is surprising.

My guess is its the parking brake or a binding caliper piston. Check if the dust boot around the piston is dislodged. Pull the rotor and inspect the parking brake.

[Chilly]

Last night I lifted the back left wheel and there was significant resistance. I'm a healthy 190 lb and could barely spin the wheel. Pulled the wheel and compressed caliper with C-clamp and it freed up. So that isolated problem to the main brake, not the parking brake.

Then I removed the caliper carrier and cleaned the funk and dried caliper grease from the slide rails. Filed off the roughness and corrosion, revealing some ruts where the pad backing plates had worn a groove. I've seen worse so I'm not convinced these are necessarily a problem but I will file down some more and massage the ruts with a Dremel sanding drum to make them into shallow waves instead of ruts. I'm not ready to replace that part just yet.

So I reassembled, stomped the brake (engine running to get full boost), then rechecked the wheel. Not as tight as the first time but still way too tight. Pulled the wheel again so I could exercise the caliper with the C-clamp. That's when I noticed the rubber boot had come loose from caliper. I could see the piston through the inspection hole in the caliper body.

Thanks, guys.

Chilly

[Manolito]

You can get a new Girling dust boot and square seal on line for $10 plus shipping.

Rebuilding brake calipers is a messy job but not too difficult. You have to be careful to keep the brake fluid off the floor and especially off your paint.

Because your piston is sticking, you will want to pump it most of the way out of the caliper before removing the brake line from the caliper, or it will be tough to pull out. Clean the rust from the piston and bore, but be careful not to scratch the surface where the square seal slides.

A new caliper is about $150. A rebuilt caliper is about $50. I don't know how good the rebuilts are, but they are probably at least as good as what you would do yourself.

[Jeron]

If you are just rebuilding one caliper you can force the piston out with pedal pressure. Pedal pressure actually pops it out pretty softly but still place a rag or a block of wood to "catch" it.

You can also remove the caliper and pop out the piston with compressed air. This can be done fairly softly with practice but its best just to let it hit wood or a rag, same as above. Dont put your hand anywhere near it in either case.

[Chilly]

Thanks for tip, Manolito. I think I'll try fixing what I've got first, then go from there if I get a leak or if it still sticks. It's not leaking now so the o-ring can't be TOO messed up. Seal doesn't look torn, just loose. Don't mean to sound too cheap, it's more a matter of time waiting for stuff to ship. I may pay in the end for trying to cut corners but I bet I can get it to cycle smoothly without waiting on parts to arrive in the mail.

I had been getting 27 mpg, thinking I should be getting closer to 29 or 30. My commute is virtually all highway at 70 mph. I'm curious to see how my mileage improves without a dragging brake.

Chilly

[Jeron]

The boot either A) wont go back in or B) wont stay in because it is now permanently deformed. Trust me.

Rebuild is pretty easy so either pull the boot and drive it like it is until the new part comes in or rebuild it now and then again with the new part. You might want to do the later depending on how long it has been dislodged and where you live because that way you can inspect the piston for damage from road salt and debris. You may need a new piston.

[Manolito]

With that mileage, I presume this is a stick shift, right?

You may pick up at tiny bit of mileage, but rubbing brakes are generally a low speed phenomena. On most cars, you can feel the brake pads rubbing on the rotors if you raise the car up and spin the wheel. Subcompact metro cars sometimes use relatively oversized square seals that will actually pull the pads back from the rotors so they alway spin freely, but highway cars don't.

Once you get up to highway speed, the hub/bearing has flexed a few times on corners and has forced even a stuck caliper piston back a little, and the spinning rotor has a very thin boundary layer of air that spins with it and tends to force its way in between the pads and rotor such that the pads 'fly' a few thousandths of an inch off the rotor at highway speed.

[Chilly]

Actually mine is an auto. Buddy has a manual 328i, same year, he gets 30 highway when he drives it carefully. Figure I should be within a mpg or two. Do you think 27 mpg is as good as it gets for an auto?

[Manolito]

I got my two daughters matching '97 328s, except that one is an automatic and the other is a manual.

All our cars have made many one-way and weekend round trips back and forth to their college (250 miles each way, mostly freeway, 75 mph) so I have many data points for highway milage.

'97 328 5sp 30 mpg
'97 328 auto 26 mpg
'04 330 auto 28 mpg
'91 Volvo 5sp 29 mpg

These are data points with me driving. For some mysterious reason, my wife and daughters seem to manage to burn more fuel than I do. Also, my daughters seem to be able to make it between our house and their college in a half-hour less time than it takes me. Hmmmmm.

[Jeron]

Here are my highway MPG's

01 330 auto> 25.5 - 27 @ 80-95mph
97 M3 5spd> 25.5 @80-100mph
91 F-150 5.8l auto> 15.5 @70-80mph
97 R1100RT> 45 @80-100mph

[Chilly]

Update:

Took caliper apart. Kept connected to line and incrementally pushed on brake until it dislodged the piston. Had some rust on the piston near where the boot was loose. Smoothed it as best I could with some sandpaper and Scotch-Brite pad. I think my pads are worn enough that the rough spot won't touch the o-ring. It might not touch even with new pads but I'm not sure. I'll probably replace the piston next time I put pads on.

Caliper bore looked flawless so I disconnected from line, removed o-ring, and cleaned the innards. Used a pick and sandpaper to clean the rust and junk out of the groove for the boot. Reassembled with the old parts (there's a technique to getting the boot lip into the groove but I can't describe it very easily) and it's working fine with no leaks. I'll probably order new o-rings and boots with my next Pelican order but for now I'm back in business and I learned something in the process. It was easy enough that I want to do all four calipers next.

Chilly