Brake squeal driving me nuts!

[mentalattica]

All stock 2007 Yukon SLT 79,500 mi.

About 2 months ago I started getting a squealing from my front driver's side under light braking so I figured it was time to change the pads and rotors. Pulled the wheels off and still had about 50% of pad life left but one of the shims had separated from one of the pads. I replaced the pads and rotors anyway and still have been getting the same squeal for the past 2 months. I tried bedding the brakes, disassembled and rechecked everything (about 5-6 times so far), recleaned and relubed using the permatex "green stuff." I replaced the caliper hardware, lubed the guide pins real good, even sanded down the edges of the pads. Nothing's working. If I lube the pad ears real good the squeal quiets down for a day or two. I've replaced Wearever Gold ceramic brakes with the exact same pad, the new rotor is Wearever too (the last was oem). Am I missing anything here or are Wearever Gold's crappy pads? They've been quiet for about 3 years and I loved them until now.

 

[mentalattica]

I finally found the culprit in case anyone comes across this problem. Turns out the brake and rotor change were unnecessary. Today after ripping everything apart again I found that 1 of the 2 pistons on the caliper were sticking. It wasn't completely seized but definitely not even close to level with the other. That explains why the squeal was only under light/medium braking but went away under moderate to hard braking. Sadly Autozone and Advance don't carry rebuild kits (locally at least, and Napa was closed) so I ended up replacing the caliper with an Autozone rebuilt caliper for about $50.

Luckily the pads were new enough not to wear too unevenly. The squeal is now gone! I can't believe I didn't notice the lack of brake responsiveness though.

 

[Justinj360]

How can you tell if a piston is sticking?

 

[mentalattica]

Take the caliper off of the carrier, pump the brakes a couple of times, then go take a look at the pistons. In my case one piston was extended about 70% more than the other.