OK, so saturday afternoon at Mid Ohio my rear brakes begin to grind a bit. I get some new pads and when I pull out the old ones, they are shaped like this:

|\ /|


The top of both pads, on BOTH wheels were almost down to metal (one was) and the bottom of the pads still have between 1/8" and 3/16" of material left. I could see the pads on one side having opposite wear, indicating a bearing problem, and I could even maybe see just one side being worn oddly if the pads stuck in the caliper crooked or something. But both sides? Has anyone seen wear like this before? When I get a chance I'm going to pull the calipers off and inspect them, but I've never really seen anything like this before.

 

Mine always wear like that. Think about it, the pads grab a moving rotor. The friction of the moving rotor pulls the pads in the diretion of rotation, making them angle a bit...

 

I can't believe that's normal, the wear left to right on the backing plate is even - top to bottom is screwy. At least someone else has seen it, thanks for the info.

 

OK to understand this better, just think of your hands grabbing onto a moving rotor from the front. Now, think of how much force the rotor will have pushing your hands down with it after you had ahold of it. It would catch on the top of your hands and push them down, which would cause the bottom of your hands to be pushed outward. Same thing is happening here, there is a little wiggle room because the pads are only held straight by two pins. They aren't perfectly rigid.

 

I understand what machron is saying, but I've been through two sets of rear pads and both times they wore normally. Is this why I saw you bleeding your brakes Saturday?

Edit: I just went and looked at my last set of rear pads (DS2500) I keep as spares. They're about half worn and look completely normal.

 

i think i have a slight taper on my track pads, if i remember right.

 

probably depends on how hard you stomp on them

 

think about it, the top sees more rotor than the bottom. only makes sense in an accelerated wear enviroment to wear more at the top, right?

 

NO, that's not right!! Pads should wear evenly top to bottom, ONLY!! Your pads are probably hanging up on the pins and not floating freely. Typically it would indicate bent pins, that was an old Volvo issue. Also verify that the caliper pistons are pushing out straight, you may have gotten a piece of the piston dust cover jammed and may be causing the issue.

PAD TAPER IS NOT NORMAL!!!

Darin

 

before your post, i never read the measurements he listed. mine are less than a 1/16 different.

 

I didn't think it was normal, I've been working on cars for over 25 years and pad taper that pronounced is just odd. I'll try and take some pics tonight, and btw may last two sets of rear pads wore normally. I'm just wondering if anyone has come across it before and what was done to correct it.

Chris: That's not the reason I was bleeding the brakes, I was getting a long pedal about halfway through each session. Although if the pads were hanging up it could very well be the cause of the long pedal. If I ever get this brake issue worked out, I might actually get a little quicker around that place...

Machron: My front calipers are black - I stomp on 'em pretty good.

 

i've been in the auto parts business for 5 years now. I see this pretty often, if the pads are wareing like that its USUALLY a sign of a caliper problem, espically because they are mulit-pistion calipers, its has even less resistance to doing this. it means one pistion is going out farther than the other, thus wareing the pads at an angle.

 

Here are the pics of the pads. I haven't had a chance to pull things apart yet, but I think these pads show the issue pretty clearly. They were wearing evenly, which makes me think that once the pads get worn down so far, they no longer move in a parallel fashion.

 

Nice theory...but it's more like each pad is trying to balance on one piston in the rear, being held parallel only by 2 pins that are hardly stable and do not even fill the entire hole they go through...and never could because the pads have rectangular holes and the pins are round lol. That's the main problem, the retension system lets the pads move around and so they get pulled downward whenever they grip the rotor, consequently angling them as shown. IMHO there is no problem and this is normal.

 

I think it's somewhat normal for a solid hat rotor to wear pads unevenly. I'm sure the rotor shape and size will affect the differences in wear rates. Extreme usage under track conditions will only exaggerate the effects. Under thermal expansion, a solid rotor will expand in a cone shape, thus causing the pad's tapered wear pattern. Whereas with a 2-pc floating rotor, the rotor will expand in the radial direction much more evenly.

I measured my race pad thicknesses before my last two track days to gauge the pads' wear rates. I do rotate my pads around to even out the wear. Kinda like rotating tires.. hehe..