71jcguy

2006 cobalt brakes worn, but no noise, so 2 days a go I changed out the front rotors and pads on a 2006 ss supercharged cobalt, they functioned correctly and operate quietly, new rotors and thermo quiet ceramic pads.
so then 1 day ago I did the rear disc, again new rotors and thermo ceramic pads. now there's a noise when applying light brake pedal pressure right before the car stops, almost a humming resonating noise that gets worse if that pedal pressure is held, if I push slightly harder then it goes away, if I lighten up it gets louder, sounds just like when a 18 wheeler is almost stopped.. . everything was cleaned, greased etc.
this is about the 500th car I've worked on but it is the newest car I've ever worked on so the rear disc brake caliper twist piston style was a little odd, but I believe I have all that correct, as the grooves in the face of the pin align with pins on back of the inner pad.

have never had this type of noise after doing any brake work....
so I removed the new pads, put in org, same noise, then I swapped out rotors with org, same noise, then put in org rotors and new pads, and yet the noise remained....thoughts?

ECaulk

iTrader: (6)

Give the pads some time to break in properly. Did you lubricate the pads and slides?

07blackg5

iTrader: (8)

the back of the pads*

cluelessk

Did you replace the rubber guides for the slide pins?

My lnf rear calipers did the same.

ECaulk

iTrader: (6)

Thank you, I assumed no one would be stupid enough to do that. Although I'm sure someone would try.

71jcguy

I did grease the slides, the back side of each pad, and the face of the piston, I did not replace the rubber guides as they where in perfect condition.

cluelessk

Mine looked perfect too. Nothing visually wrong at all.

71jcguy

okay, so I tore it all apart again check over everything, nothing can I find incorrect or showing signs of any improper contact or wear....so I am going to replace the entire rear calipers next. hear there are a lot of issues with these twist type caliper that incorporate return/spring and e-brake function.
I suspect that those have something is not functioning correctly with them.

cluelessk

Use brake lube on back of the pads where the caliper puts pressure. Pads are probably coming into contact with the rotor slightly.

71jcguy

"I did grease the slides, the back side of each pad, and the face of the piston, I did not replace the rubber guides as they where in perfect condition."

71jcguy

well, I still don't know what it was that made my brakes sound like a semi braking....but I swapped out the calipers w new one, put the same rotors and pads back on and the noise is gone...but I did notice after having the org calipers off and inspecting them further that the e brake spring setup did not rotate as "freely" as the new calipers and the pistons did not rotate as easily either. either way new calipers took care of it, the brakes are silent once again.