Hi Folks,

Chronic problem for the 5 years I've owned my beloved 83 GSL. The rear brakes groan at very low wheel rpm.

32K Miles, all stock.

Check out some video here:

https://drive.google.com/file/d/0B-l...ew?usp=sharing

In that video, I am pushing the outboard pad away from the rotor, detail:



The noise happens when I start moving forward and upto ~5 MPH. If I lightly tap the brakes or pull up a bit on the ebrake, the noise stops, let off and it starts again. It happens whether cold or hot, just a bit less when warmed up. Always loud and annoying first thing.

It never happens in reverse.

The calipers are the original ones, but the pads and rotors are new (from BlackDragon) OEM stuff. A professional brake guy did the work, and he's been back at it a few times over these years trying to really fix it. He's tried new pads, deglazing them etc. But this happens immediately after he's worked on it so there's no time for the pads to glaze as far as I can see.

I don't want to just throw in new calipers unless that's really the answer, I've spent so much on this so far.

Thanks!

 

I say it could be:

1. Warped rotor - rotors are cheap.
2. Warped/bent axle matting surface.
3. Maybe the axle retaining bolts need to be tightened up.
4. Bent caliper bracket.

 

Thanks, especially for considering all of my noob questions.

I found that the caliper has a torn piston boot, picture below. Could that be the reason? Weird as it seemed like the outboard pad was "floating" on the rotor and then vibrating when no brake pressure is applied. I would think a stuck caliper would fail to return and apply too much pressure. Is there supposed to be a spring between the outboard pad and the caliper mating surface? I've got the shim pads, like #2 in this diagram and there's the anti rattle spring in 2nd photo:





Either way I gather I need to replace both rear calipers? Do you guys like the stuff on Rockauto?

To be thorough, though, I've checked your other suggestions.

Rotors, no run out.

I took off the caliper and pads, and spun the wheel as I did before, no noise whatsoever. So does that rule out problems with the axle mating surface and retaining bolts?

The caliper bracket looks "good" as far as I can tell, I checked it to be parallel to the rotor:




Torn caliper piston boot:


Best,

Tom

 

I can tell you exactly how that boot got torn up. It was torn when the caliper piston was screwed back in when the brake job was done. I've done the same thing before.

That gap is caused because the piston is not extending enough. Might try manually extending it some and then bleeding that brake.

or

Buy new calipers. I've rebuilt calipers before and it's cheap, $2 per caliper, but a pain in the *** for me. Rock Auto is good but it appears they don't have the rear right in stock.

 

I just ordered a couple of rebuild kits for the calipers...as you said no rear right in stock at RockAuto and I couldn't find them elsewhere easily, so I guess I'm rebuilding them. Tough job? Not rebuilt calipers before.

First though, I'm trying your suggestion to extend the piston and bleed.

Tom

 

Fixed! Fingers crossed at least.

No more groaning sound in a couple of test drives with lots of hard braking and slow start up. TL;DR = it was missing some shims and I rebuilt the caliper, no more noise.

I think the real fix was, not surprisingly, using all of the anti rattle hardware that is supposed to be on the caliper bracket. I was missing two of the springs. They are part of the rear disk hardware kit that is out of stock at Rock Auto, and costs ~36 + SH from Atkins and also Mazdatrix. I was reluctant to pay close to $50 and to wait for the parts when I only needed two of the springs in the kit. So I made the ones I needed out of stainless sheet stock from the local Ace. Luckily, the ones I needed were more shims than springs...the stainless is strong but more malleable than spring steel properly annealed etc.





I also had already gone down the caliper rebuild path and it was really easy. If you don't have to disassemble with the parking brake/adjuster stuff inside the big rubber boot, it's just a matter of unscrewing the piston, cleaning everything up, lubing, and replacing the seal. You can brush out minor rust from the bore, but use only plastic bristles and brake cleaner to clean the piston's seal surface. Screw it all back in and Bob's your uncle.

On the piston insertion, I screwed it in completely, overshooting the line up, and then unscrewed a bit to adjust the extension enough to just go over the installed pads. Trial and error going and backing off. This sort of "pre-adjusts" the piston. Prob not necessary, but it worked for me.

I used a vacuum bleeder to flush the system.

So far so good! Thanks for all the advice and clever thinking.