I've been having an issue with a squeaky rear disc brake for quite a while... it only makes noise when the brakes are applied, and usually with a light-to-medium force. In other words, every time I slow down for a stop sign, etc. I hear a "chirp chirp chirp" coming from the back of the vehicle.

The rotors are new, as are the pads. I rebuilt the calipers with the "upgraded" J65 rear disc kit to fix the usual parking brake issues. The rotors show no signs of abnormal wear and the pads look fine, both front and back (in case they were moving within the caliper). Since this is a metallic-sounding noise, I figured there would be some kind of metal-on-metal wear, but I have found nothing.

So I lubricated the slide bolts and rubber inserts on the caliper, because they were really dry and stuck. The rubber pieces on the outboard side of the caliper (holding the tips of the bolts) were pretty trashed, though, with only about half of the piece there. I don't know if it's causing the caliper to move around or not.

I also checked if the axle shaft was bent using a highly technical method -- clamping a flexible piece of metal to the dust shield and moving the end so that it barely touched the side of the hub, and then spinning the shaft. It did not rotate completely true, but I don't have an exact number -- I'd say there's 1/16" runout if I had to guess. I checked the other axle shaft and it was about the same (although I left the rotor on that one; I didn't feel like pulling everything apart on that side).

After putting it back together, the squeaking improved marginally. I'm wondering if those worn rubber bolt inserts are causing the caliper to move around or if the real problem is the axle. Even if I could replace the rubber pieces, I have no idea if they can be purchased individually. What do you think?

 

maybe if your axle is bent even just a little it could have worn out your rear axle bearing this could be causing the squeak

 

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Hopefully you used the stop squeak compound between your cals & pads.
But it can wear out so it ain’t a guarantee. ‘Bout the squeak modulating with
rotation. If you're are a fiercely hard braker like I am you can warp
your rotors enuff to make the squeak modulate.
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Thanks for the suggestions, but it turns out I have at least one (slightly) bent axle shaft. I put the rear end of the car on jack stands and let it run whilst in Drive to see how the hubs rotated -- not the safest thing to do, but it worked.

Now I gotta figure out what I'm gonna do... those Borg Warner rear ends are pretty nice compared to my 10-bolt.