Sticking caliper troubleshooting

[Ohthetrees]

Hello all, long time appreciator of the forum, but this is the first time I've had occasion to post.

TLDR: sticking front left caliper despite caliper rebuild. What next?

Long version:
I have a sticking left front caliper. Symptoms are overheating rotor, even at surface street speeds. 10 minutes of driving, and my rotor will be 700° read by IR thermometer.

History: I've been tracking the car about six times per year the last two years. Only 13,000 miles on the car. New brake fluid once per year, changing pads as necessary, 3x so far. Last time out, started with about half thickness pads. Normally, I read about 700° after one cooldown lap. As my confidence grew, and with instructor in the car, I started hitting 140 mph every straight. I'm sure my brakes got hotter than ever before. My brake light came on, but since I was paying for not only track time but an instructor, I made a mistake and told myself I would check it after the session. Having started with 1/2 pads, and knowing my wear rate from previous 10 or so track days, I assumed that a sensor had overheated and failed due to more aggressive braking. Please don't reply explaining all the ways this was stupid, I know all the ways this was stupid. I was stupid. Anyway, a few laps later the brakes started to feel funny, and I came in. Big wet smears of melty compound on front rotors, which were smoking, and I was pretty down to the backing plate. After cool down, dash lit up with warnings, abs disabled, etc.

What I did:
Replaced pads on all 4 corners with Pagid RSL pads. Replaced sensors. Replaced brake fluid. Reset computer.

All seemed well when I went around the block, brakes felt good, no pull. But on a longer drive, I heard some noise on the front left, pulled over and FL rotor was very hot. Luckily I had my IR thermometer with me. FL 700°, FR was 125°.

Rebuilt front left caliper and replaced fluid again. Dust boot had slight heat damage, the O ring (or whatever the inner rubber ring is called) looked absolutely perfect. Cylinder bore and cylinder were glossy smooth perfection. While I was at it I replaced guide pins and rubber guide bushings. Thorough cleaning, greased all sliding surfaces.

Put it all together, no joy, still overheating. Put stoptech Street pads on, and problem was much less severe, only 25° temperature differential between front rotors, which I regarded at the time as within the natural variation range, so I decided to blame a defective pad from Pagid. I thought perhaps crooked or distorted backing plate. My wife (less aggressive driver) then did a track day, and I had her monitor it every session to be safe. Problem was back! 700° FL, 400° FR. As 700° is well within safe operating temperature, she went back out, checking temperature twice per session. The differential temperatures slowly improved over the day, last session differential was only 25°. The 300° differential at the beginning of the day clearly showed that there was still an issue, but I thought maybe it had sorted itself out by the end of the day, so I put the pagid pad back on. Oops, driving only 45 mph for a few minutes on streets, problem back, left front to 700°, right front 100°.

So the problem is definitely exacerbated by the pagid pads, but still there with the stoptech. The Pagids are noticeably thicker than the Stoptech, and during my wife's track day symptoms got better and better over the day as the pads thinned, so I think pad thickness is in exacerbating factor, but clearly it's not the whole story.

So where do I go from here, could I have warped my entire caliper and/or carrier? Should I replace the caliper, or could there be other issues?

[roastbeef]

interesting. you're thorough in describing the problem and already did what i would have thought to do... not sure where to go from here, but i'm interested in hearing what more knowledgeable people have to say.

[drrust]

My experience with sticking calipers was on an E36 M3. Would get vibrations at highway speeds especially after light application of brakes. After a mechanic had rebuilt the rotor it had returned after several months. Mechanic replaced piston with a stainless version that was available from Bimmerworld.

It was mentioned that there were sing a if corrosion in the piston, so this may not be the same cause.

[Ohthetrees]

Update: I bought a used caliber ($110), cleaned and rebuilt it, issue gone. Yay! I'd be interested if anyone had any ideas about what could have happened to the old caliper. Visually it was perfect, bore and piston looked smooth and perfect. No obvious problems with caliper or carrier. Anyway, all is right with the world again. Thanks!

[GRM Scott]

I had a similar problem with the right rear caliper on a Spec E30; something was just wrong with the caliper and it would bind hydraulically, couldn't bleed pressure when the pedal was off, and as the heat rose due to dragging the pressure increased and it would just clamp harder and harder. Tried damn near everything, inspected lines, fiddled with the caliper, etc. The ultimate fix was a complete swap of the caliper (borrowed from a buddy who had crashed his car earlier in the weekend). Chalk it up to gremlins.

[drrust]

Glad to hear you solved your problem. However, not happy to hear the E9x also can have this issue.

[Ohthetrees]

To be fair, I grossly overheated the pads and ran them down to the backing plate. I imagine much more heat is transferred through backing plate than through healthy pad material.

[RickyBobby]

Did everything operate smoothly when you out the caliper back together? I.e. Did the piston move smoothly in he cylinder? Did the caliper slide freely when you installed it back on the car?
I recently chased down a similar issue on my e36. I ended up rebuilding all of the calipers and bleeding the crap out of the entire system. My theory is that I had a stubborn bubble on the other side of the car that was causing it to squeeze slower than the overheating side.

[drrust]

On the E36 there was definitely an issue with the piston pitting and causing uneven braking. This is what fixed the problem:

http://www.bimmerworld.com/Stainless...Set-Ate10.html

[Ohthetrees]

The faulty caliper moved easily on the carrier during the install, until clamped in place by depressing the brake pedal. Felt exactly like the FR which isn't dragging. When I rebuilt it, I couldn't get the piston back in the bore by hand, I ended up using a c-clamp, but it didn't feel like excessive force, and was smooth. It felt exactly the same when I rebuilt the used replacement, and that one works perfectly.

The faulty caliper's piston itself was glossy, smooth, and visually perfect, as was the bore.

The used caliper was only $110. Any effective repair on an M3 that only costs $110, I'm happy.

[admranger]

Where'd you get an ///M caliper for $110? That's an impressive find!

[325rider]

Just had my full rotors and pads replaced at 56,xxx miles and right rear caliper is sticking on the new rear rotor...
$450 more for new caliper and fluid flush. -__-

[Ohthetrees]

Originally Posted by admranger

Where'd you get an ///M caliper for $110? That's an impressive find!

eBay! That price included shipping! I was kinda nervous because brakes matter, but the seller (mporiumbmw) had 100% positive feedback, and deals exclusively in ///M parts. The caliper is in very nice condition.

[bigjae1976]

Probably needed a new piston.

Originally Posted by admranger

Where'd you get an ///M caliper for $110? That's an impressive find!

I sold my entire set of 4 for $80. Plenty of used calipers laying around.