Warping rotors

[letitsnow]

I have a bit of toe wear, but no crazy unexplained tire wear problems. I'm not doing much heavy repeated braking, just street and autocross, no track days/HDPE. I think there were hard spots in these rotors after I turned them and that's why they still shake. I think the runout wasn't great when I put them on and that's why they wore funny in the first place.

 

Tie rods are in decent shape, don't feel loose, inners also feel alright.

 

Everytime I've asked someone about brake shudder, they link me to that stoptech article. I believe they are correct, but I'd say that it's only true on a well setup system, I think I have another issue somewhere, could be the hub has some runout, could be a wobbly bearing, could be rotor runout, could be a sticky piston.

 

I think I'm going to buy another set of rotors(I'll try the $20/pop centrics this time), and set them up with my dial indicator and some .001 shims and get them as straight as possible(going to shoot for *<.001"). I'll rebuild the calipers and replace the bearings too. The pads are about 50% gone, but I should probably replace them too.

[Xnke]

I've always been taught that new rotors always got fresh new pads, and anytime you change compounds on the pads to sand the rotors down with garnet paper, wash with brake cleaner, then bed in the new pad compound. Supposedly it's bad juju to mix pad compounds on the rotor; I dunno. Seems like lots of folks do it anyway.

 

That said, I too have this issue, and my car also pulls to the right a little on braking. Got an alignment done and it went away for about four months, now it's back again. (the pull, not the vibe)

[bjhines]

I really think there is something not considered. You are talking about shimming the rotor straighter than I think is needed. There is always some run-out in the rotors. The brake calipers can accommodate this run-out fairly well. You may have a sticking caliper piston that causes a large amount of pressure on the rotor as it wobbles. You need to inspect the calipers and check that the pistons move without binding or sticking in their bores.

 

The calipers can allow for some runout by allowing the pistons to move back and forth with the wobble. A sticking piston or blocked fluid passage would bind when the rotor wobbled.

 

If you find that one or more pistons is sticky, then you need to fix the problem and replace the rotors. The dragging piston would wear the rotors to varying thickness. The sticking piston would wear the dragging area of the rotors thinner. This would cause the rotors to behave the same way, even when the calipers are renewed. If you have this problem you need to replace the rotors after you fix the calipers.

 

Keep in mind the calipers can accommodate rotor run-out, but they cannot accommodate varying thickness. This is one of the reasons the wobbly brakes issue gets worse as wear progresses. You eventually end up with two problems.

 

If the car pulls to one side then you have a bad caliper on the opposite side.

Edited August 15, 2012 by bjhines

[letitsnow]

That is high up on my list of things to check, I replaced the calipers not long ago, but that doesn't mean one isn't sticky.

[letitsnow]

I think I'm going to go back to a 'normal' pad compound(from porterfield r4s) in the front to try and get some more bias in the rear until I can budget in a rear disk swap.