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E36 M3 (1992-1999) {Euro - S50 B32 321hp @ 7400 rpm} {U.S. - S52 B32 240 hp @ 6000 rpm}
Total Produced: 71,212 - Years Produced: 1992 to 1999


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Old Thu, Jul-12-2018, 05:05:58 PM   #1
abcurran
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Default Year-old Brakes, a Warped Rotor and Recurrent Sound

Trying to track down a recurrent sound from the brakes, that I thought I had sorted...

About this time last year I overhauled the brakes. The euro floating rotors (that a prior owner bought new from the dealer in 2001!) had about 75000 miles on them. Pads were pretty thin. And I had already rebuilt one front caliper to fix a stuck piston.

I got a free set of front OE calipers from a friend with a crashed car. Disassembled, de-greased, blasted, and painted with POR 15. The Bores and both pistons were in good shape - one piston had maybe a 2mm sized pitting mark that wasn't very deep from corrosion. Both had some light scoring. I was able to polished out the scoring and much of the pitting so here were no high points. The rear calipers I just resealed. New Brembo blanks and Stoptec Street Performance pads. New ATE fluid.

No issues with install. No issues on first drive and bedding. Brakes rode fine and functioned properly for about 6 months.

In January, I refreshed the front suspension with refurbished control arms and FCABs, with Lemforder bushings and ball joints (Thanks, Brett!) new Lemforder inner and outer tie rods, and Lemforder sway bar end links. Work was done at competent shop that I've been going to for years.

By March this year, (~6 months after brake install, ~3 months after front suspension install), the car developed an audible metallic clicking sound when applying the brake. It wasn't every time I pressed the brake, but more often than not. There was no decrease in brake performance, and no vibration in the wheel or pedal. Visual inspection didn't show anything.

But, over time it worsened such that I could produced the noise any time I pressed and released the brake performance was still not affected, but I noticed it would pull to one side when braking.

The culprit was a caliper guide bolt that had backed out of the the bracket. The sound was the caliper twisting every time the brake was applied. The result was a warped caliper from uneven pad pressure to the rotor.

Last month I had the rotor cut. I reinstalled the rotor, replaced the guide pin bushings with a spare set, and installed and re-torqued the caliper guide pins to spec. Problem immediately went away - albeit there's a very slight steering wheel shake when braking above 40 mph, which I consider to be a still slightly warped rotor or uneven pad. The shake, however, is not the problem.

The problem is that the sound has reappeared about two-three weeks after it went away. It sounds identical to when the guide bolt was loose. But, the guide bolts are not loose. I checked immediately, and they're torqued to spec, which, if I can recall the Bentley from memory, is 22 lb/ft. The sound does seemingly stop after the brakes get some heat. So it might make the sound for the first 5 minutes of driving.

Other than the piston binding in the bore then releasing, what else should I be looking for?

Should I over torque the guide pins? Loctite them? Do guide pins stretch?

I guess it's possible that some paint got onto the threads on the caliper bracket, such that the guide pin isn't properly torquing. that will be easy enough to clean up. I don't think this could be the problem because the brakes functioned fine for 6-7 months after rebuild.

Any other suspension pieces that would make a sound similar to a loose caliper when the brakes are applied?
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Old Fri, Jul-13-2018, 04:37:51 AM   #2
englishtom1596q
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Default Re: Year-old Brakes, a Warped Rotor and Recurrent Sound

its probably just your heat shield rubbing somewhere. Maybe when you apply brakes the caliper is contacting it and moving it into the rotor or something silly. I doubt its your guide pins. Did you do guide pin bushings? these could allow the caliper to move more than its supposed to and contact the shield.
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Old Fri, Jul-13-2018, 11:22:09 AM   #3
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Default Re: Year-old Brakes, a Warped Rotor and Recurrent Sound

Have you tried brake grease?
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Old Fri, Jul-13-2018, 07:21:42 PM   #4
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Default Re: Year-old Brakes, a Warped Rotor and Recurrent Sound

Quote:
Originally Posted by englishtom1596q View Post
its probably just your heat shield rubbing somewhere. Maybe when you apply brakes the caliper is contacting it and moving it into the rotor or something silly. I doubt its your guide pins. Did you do guide pin bushings? these could allow the caliper to move more than its supposed to and contact the shield.
Interesting thought. I doubt the caliper moves that much, but worth a shot.

All guide pin bushings were replaced when the calipers were rebuilt. Original OEM rubber bushings, not brass. I replaced the offending caliper's bushings when I discovered the loose pin with a spare OEM rubber set I had laying around.


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Originally Posted by pbonsalb View Post
Have you tried brake grease?
Liberal amounts behind the pads. Anywhere else you suggest?
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Discussing Year-old Brakes, a Warped Rotor and Recurrent Sound in the E36 M3 (1992-1999) Forum - {Euro - S50 B32 321hp @ 7400 rpm} {U.S. - S52 B32 240 hp @ 6000 rpm}
Total Produced: 71,212 - Years Produced: 1992 to 1999 at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)