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Discussion Starter #1
I have a problem with my rear brakes. Car is a '98 GT with Brembos up front and Cobra rears. The left rear caliper is experiencing some uneven pad wear, with the top of the outboard pad wearing out fastest. After replacing the pads it occurred to me to check the rotor temps, so after my morning commute I hit them with my infrared thermometer. The left caliper was around 190º and the right one about 130º. So obviously something is dragging.

When I replaced the pads I didn't notice any sticky slide pins, in fact the sliders moved in and out real easily. I also didn't notice the piston being any more difficult to rotate back into the bore than the passenger side, but since these things are usually a PITA to rotate, it's hard to tell for sure. Do rear calipers get stuck, like the front ones can? And will they rotate back in if they get "stuck?"

Or could the problem be something else?
 

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Sounds like one of the nubs isn't fully seated/pison not rotated enough(too much)like 90lx said.

Also, did you use any shims/washers with your rear upgrade to achieve a desired alignment between rotor/bracket?
 

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Discussion Starter #4
Doh! OK, I'm a dumbass. Will reset pistons so the nub on the pad is in the notch, assuming the weather dries out by this evening, and recheck temps again on tomorrow's commute.

Tony: no shims needed, just a little grinding. Had some groan, which I initially thought was bracket-rotor contact but turned out to be the diff wanting friction mod (it looked like there was plenty of clearance!).
 

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I still have an ever so slight drag on the rotor, but it's so insignificant i'm not busting the wheel back off and R/R'ing the parts. It'll clearance itself soon enough. ;)

Wonder what the consequences of grinding the pad nubs completely OFF?!
 

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The piston could rotate with parking brake use and cause the pads the drag.
Not just that, but the rear brakes wont adjust properly and your parking brake may or may not work. The nubs keep the piston from rotating, so when you pull your parking brake, the screw mechanism rotates, the piston does not, so the piston will move toward the rotor. When you release, it then sucks it back in.

Basically, the piston is the nut, the parking brake mechanism is the bolt, and the nubs/brake pad is the wrench. No wrench on the nut, and you'll be spinning the bolt for hours.
 

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What would cause moaning/vibrating rear brakes during cornering? For the last HPDE, I installed Hawk Black pads in the rear (Brembo up front with Hawk Blues, Cobra rear with Hawk Black). The rear brakes would moan, vibrate and drag during cornering. After each session, I turned the Prop Valve toward "less brake." Currently it is "all the way out" and there is still the same result. I lined up the nubs when installing the new pads. I have yet to check to see if they're still aligned.

The street pads would sometimes moan, vibrate, and drag during street driving, but with less intensity. No anti-moan brackets. Previously, the rear brakes only made some noise when reversing
 

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Discussion Starter #11
OK fellas, I R&Red it all last night, aligning the notches with the nubs on both sides. On the commute this morning I got 170º on the "problem" side, 145º on the "good" side. So there's still a temp difference, but it seems the problem side has gotten better while the other side has gotten worse. Sigh.

What kind of rotor temps should I be expecting? If one of you fellas has an infrared thermometer can you do me a favor and check on your next 30- or 40-minute drive?

One question though: there was some clearance between the piston and pad after I put them back together; would pulling the parking brake misalign them again? How is one supposed to get the piston to seat against the pad?
 

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Your rear temps should be fairly close to your fronts, IMHO. The individual readings between different IR thermometers and different cars isn't going to be helpful to you.
 

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When doing rear pads, i've always been able to seat the pad against the piston. :confused: How far did you turn that sucker?!
 

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Discussion Starter #14
Maybe too much. :) Perhaps I'll try again and try to get it so there's just enough gap between piston and caliper outboard face to slip over the pads and rotor.

Your rear temps should be fairly close to your fronts, IMHO. The individual readings between different IR thermometers and different cars isn't going to be helpful to you.
Maybe not. Anyway, I think my front temps are every so slightly lower. They are Brembos, after all.
 

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Discussion Starter #15
OK, so I think the caliper situation is resolved for now, but I've discovered that I have a slightly bent axle and a squeak that I think is the axle bearing. I'm assuming a bad bearing and/or bent axle would cause some extra friction, which might be causing the extra 30º at that side.

So two questions: what's a good source for a new axle? And is it necessary to replace both, or is OK to just replace the bent one?
 

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I don't see how another used or even a new one would have any consequences. Maybe time to upgrade to some better ones, though.
 

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The noise is probably from the rotor pushing the caliper back and forth as it rotates and the the pads are squeaking where they contact the bracket. The bearing won't squeak since it is covered in 80w-90.

There is no issue in replacing one axle at a time.
 
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