Smoking rear brakes...literally. Need help with causes.

[bimerguycw]

Sorry, this is a detailed help request before I just start replacing damaged parts.

I have had smoking from both rear brakes today after noticing that the car felt like the car was dragging from idle the parking brake was still released to start driving (And no the hand brake level was not up) and then they apparently got hot enough in the travel distance about 10 miles to begin smoking at a stoplight and I had it towed knowing from the smell and smoke that it was binding.

While waiting for the tow truck I checked the rear brake binding again after sitting with the parking brake off about 40 minutes later and the car could move freely with idle speed with no binding as before.

By the way, these rear rotors and pads were new about 6000 miles ago and never had this symptom until now.

Once I got the car towed home the rear brake binding was still not there and I removed the wheels to rotate the wheels and they rotated freely. Visually checked caliper piston sticking or parking brake binding and neither had a problem when using them while car jacked-up and rotating while trying the parking brake or calipers with someone in the car...but obviously not hot enough as before. The pedal and hand brake would both slow/stop the wheel rotating evenly when checking. No catch places around the wheel rotation during this test just smooth rotation and braking.

The advice I need is in my findings when I removed both rear rotors and found:

1) The rotors' parking brake shoes inner surfaces where bluish-purple-black on 80% of the contact area(Over-heated)
2) The parking brake shoes had cracks across them in about 4 places but thickness even and a little less than 1/4" thick.
3) The disc rotor surface was overheated looking but not nearly as much bluish coloration as the inner shoes surface.
4) The 6 mo. old disc pads were overheated and looked like a rough grinder was used along the flat surface(rather than smooth, glazed surface). And the paint was peeling of course from the heat.
5) The pads thickness was 90% remaining and even thickness.

This is the same and even for both rear wheel brakes. I had noticed that the parking brake light flickered on a few times over the past several weeks but never stayed ON and no dragging noticed at that time; if that has any value to the likelihood that the parking brake needed adjustment and cause dthis problem. I thought the Parking Brake light was just triggered for the hand lever being up and making contact regardless of brake adjustment.

Obviously, I will have to replace these rotors, discs, pads, shoes and not willing to do this until I know the cause as it may happen again so please add your experiences from these symptoms.

I'm unsure which caused the problem:

1) A sticking/binding parking shoes( Do these require greasing/lube in the cable assembly over time?)
2) A binding/sticking caliper pistons(ususally 1 vs. both at the same time.
3) A master cylinder flaw in this 1/2 of the hydralic circuit
4) A combination of these like a binding parking brake shoes and then indirectly overheating the rotor to then bind the pads while driving at speed to add more overheating.
5) Or something else that control the rear set like ABS.

[Ferret]

My first thought would be to get someone to repeatedly move the handbrake while you're under the back of the car watching the handbrake cables - see if the cables have a 'lag' in them that's caused by them sticking.

I suspect that your parking brakes have stuck, overheated the rotor and caused it to warp to the point where it's binding in the rest of the setup...

[whiskychaser]

I suspect that your parking brakes have stuck, overheated the rotor and caused it to warp to the point where it's binding in the rest of the setup...

x1. Would be looking closely at the cable as both sides are affected. Sounds like that stuck in the 'on' position -your handbrake lever would not be under tension so it could bounce up and trigger the handbrake on warning when you hit a bump.

[bimerguycw]

Thanks for the feedback.

I feel like the root cause is the parking brake shoes since they are the most over-heated by bluish color but what is the proper way to get this system permanently corrected?

Do they get some grease/lube ike WD-40 or lite grease sprayed in to the places of openings or what. Bentley does not say much about these cables. I expect it can't hurt to spray a light lube into the park brake cable ends that are open, right?

I will check out the parking cable action tonight and see if it seems to bind or something.

I suppose if that's not it, then I'll go to the shoes' springs pull-back when handbrake released but that's kind hard to observe with the rotor on and it's on the inner surface. As said before I've checked for handbraking binding or point binding by rotating wheel with park brake off.

So, I guess it's intermittent in the parking brake system and I'll check it the best I can and maybe you have some definitive suggestions on this basic system.

[whiskychaser]

Thanks for the feedback.

I feel like the root cause is the parking brake shoes since they are the most over-heated by bluish color but what is the proper way to get this system permanently corrected?

Do they get some grease/lube ike WD-40 or lite grease sprayed in to the places of openings or what. Bentley does not say much about these cables. I expect it can't hurt to spray a light lube into the park brake cable ends that are open, right?

I will check out the parking cable action tonight and see if it seems to bind or something.

I suppose if that's not it, then I'll go to the shoes' springs pull-back when handbrake released but that's kind hard to observe with the rotor on and it's on the inner surface. As said before I've checked for handbraking binding or point binding by rotating wheel with park brake off.

So, I guess it's intermittent in the parking brake system and I'll check it the best I can and maybe you have some definitive suggestions on this basic system.

Unless you have adjusted the shoes up they shouldnt bind as there are pretty powerful springs pulling them into the 'off' position. So either the linkage at the hub or the cable seized. I'd be going for WD40 as its easier to point and spray and I'd be looking particularly for 'rusty' water coming back out of the cable ends

[Tiger]

Parking brake is at fault. Replace parking brake pad... scour all rotor surface with sandpaper or use wire wheel attachment on drill bit... Scour the brake pads... reassemble.

Reset the parking brake loose. When you pull up the parking brake level, it is almost like 5 or 6 clicks to lock wheel... if less than that, your parking brake is too tight. Check and make sure the parking brake pad spring is still in good shape.

[bimerguycw]

Unless you have adjusted the shoes up they shouldnt bind as there are pretty powerful springs pulling them into the 'off' position. So either the linkage at the hub or the cable seized. I'd be going for WD40 as its easier to point and spray and I'd be looking particularly for 'rusty' water coming back out of the cable ends

The linkage was consistently smooth and free to expand the shoes and then pull them back.

I vacuum-dusted the entire shoes/park brake asm portion of each side and checked binding and again smooth and even on both sides.

While cleaned I sprayed white lithium grease int the linkage on each side while the wife actuated the linkage to coat the pivot point.

Did not appear to be any water/rust residue like possible water rusting causing binding at wheel hub.

[Phatty5BMW]

Yea sounds like yours maybe a parking brake issue, but I had this case a few months ago. I had 1 caliper in the rear that was sticking without previous occurences, took it apart and cleaned, works like new. 2 weeks later the other caliper same thing. Took the piston out, cleaned works like a champ. I thought it was p-brake but sure wasn't!.. Might be somethin you want to check out.

-Pat

[TC535i]

What if when you release the cable up front, it's still stickign in the rear? Maybe it's hanging up on something, have a friend engage/disengage cable while you're back there to make sure it's releasing?

[bimerguycw]

Parking brake is at fault. Replace parking brake pad... scour all rotor surface with sandpaper or use wire wheel attachment on drill bit... Scour the brake pads... reassemble.

Reset the parking brake loose. When you pull up the parking brake level, it is almost like 5 or 6 clicks to lock wheel... if less than that, your parking brake is too tight. Check and make sure the parking brake pad spring is still in good shape.

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Since the parking brake is likely the fault what do ya' think made this suddenly become a problem? Or should I even worry about that and just replace shoes and spring kit as the culprit? I checked the shoes actuation with rotors on and off and they worked with no apparent resistance or binding but clean and lubed the level anyway.

Have you seen this happen before? It sound like you've "been there and done that" kinda thing since you suggest re-using the pads and rotors even with bluish over-heating and roughed-up surfaced rotor pads. Wouldn't we expect the rotor to be warped from over-heating and such smoking clouds from them or are these parts capable of sucg over-heating and repairable? Should I have the rotors turned instead. I know their rear brakes(approx. 20-30% braking) and does that factor into your comments about just re-surface and re-use.

The park brake handle was set to 5-6 click to lock the parking brake on hulls etc. so I feel like they were adjusted close to right.

Thanks for the great advice/experience and I just want to go through this once and be sure it's not going to be something else, ya' know what I mean.