Uneven Pad Wear in the Rear

[eng_man]

Brembo rotors, PBR pads. Reused the stock shims since the PBR pads didn't come with any and the guy at Advance said they don't sell shims since they usually come with the pads

Linking the pictures in case anyone is on dialup (the poor bastards)

http://engman.spymac.net/images/car/...or_caliper.jpg 44.7KB
http://engman.spymac.net/images/car/...or_outside.jpg 79.7KB
http://engman.spymac.net/images/car/...side_close.jpg 66.1KB
http://engman.spymac.net/images/car/...tor_inside.jpg 80.0KB
http://engman.spymac.net/images/car/...side_close.jpg 60.9KB

Now the weird part ... its wearing exactly the same way on both sides

I'm in the process of putting the stock pads back on to see if that fixes anything. Any one have any suggestions as to why they're wearing like this? Everyone I've talked to already has basically been stumped.

[eng_man]

Before I put back on the stock pads I measured them and they are worn exactly the same way the PBRs are wearing now. The difference between the top and the bottom of the pad is about 0.5mm. I haven't actually put the stock pads on, but I'm nearly positive they would contact the rotor completely.

So it seems that the car has always been doing this, so now the question is how to fix it?

[240KAT]

soudns like your calipers.

[eng_man]

Originally Posted by 240KAT

soudns like your calipers.

Ok ... anything in particular on them that would cause this?

[zero.counter]

How did you set the pads back in the shims? Could you take a picture with them on so I can ascertain from there on?

[zero.counter]

I see part of the shim on the first pic, but a better one would be better.

[eng_man]

Originally Posted by zero.counter

How did you set the pads back in the shims? Could you take a picture with them on so I can ascertain from there on?

By shims you mean the pad retainers? Hopefully this picture has what you're looking for, if not could you clarify what you want a picture of.

http://engman.spymac.net/images/car/brakes/caliper.jpg 49.1KB

[citizen]

tell you what, wearing faster on the outside is normal. heres the reason why: the outside of the rotor spins around a larger radius, so it travels around at a faster speed. faster speed equals more enegry, more energy equals more friction/heat, the more friction/heat the more wear. not much you can do except change the laws of physics.

[idlafie]

Originally Posted by eng_man

Brembo rotors, PBR pads. Reused the stock shims since the PBR pads didn't come with any and the guy at Advance said they don't sell shims since they usually come with the pads

Linking the pictures in case anyone is on dialup (the poor bastards)

http://engman.spymac.net/images/car/...or_caliper.jpg 44.7KB
http://engman.spymac.net/images/car/...or_outside.jpg 79.7KB
http://engman.spymac.net/images/car/...side_close.jpg 66.1KB
http://engman.spymac.net/images/car/...tor_inside.jpg 80.0KB
http://engman.spymac.net/images/car/...side_close.jpg 60.9KB

Now the weird part ... its wearing exactly the same way on both sides

I'm in the process of putting the stock pads back on to see if that fixes anything. Any one have any suggestions as to why they're wearing like this? Everyone I've talked to already has basically been stumped.

Before I put back on the stock pads I measured them and they are worn exactly the same way the PBRs are wearing now. The difference between the top and the bottom of the pad is about 0.5mm. I haven't actually put the stock pads on, but I'm nearly positive they would contact the rotor completely.

So it seems that the car has always been doing this, so now the question is how to fix it?

Hmmmm....you didn't mention it in your original post so I decided to check your profile to see what year your car was....97 eh? I was going to say it might have been due to possible overtightening, or uneven tightening of the lug nuts in relations to the rotor..(clamping force of brake rotor/wheels/rims to hub uneven possibly)...but that wouldn't really apply if you had a five lug hub in comparison to a four lug hub. Then it dawned on me that it's possible that the bearings on the rear hubs may be worn or shot. Have you inspected them lately??
I don't think the problem is with your calipers as you mentioned that the pads you've installed have worn the same on both rear sides. But then again I could be wrong. The pads in the stock rear calipers kinda float within the clamping portion of the caliper. Bout the only thing I can think that would affect that floating action would be either worn caliper pins or sticking/binding caliper pins. When you swapped the brake pads out on the rear the last time you serviced the brakes, did you clean & re-lubricate the caliper sliding pins? Are the caliper sliding pin boots still in good shap?? Other than that, about the only thing I can think of is either air in the line, (but you would notice that), OR maybe a stuck/misaligned E-brake cable or cable binding in the E-brake system/assembly. You might want to check those out too.
Good luck trying to figure this one out...it's gonna be a doozy...And when you do, let us know so we know what to expect in the future. Anyhow, hope this helps...
ID

[eng_man]

Originally Posted by citizen

tell you what, wearing faster on the outside is normal. heres the reason why: the outside of the rotor spins around a larger radius, so it travels around at a faster speed. faster speed equals more enegry, more energy equals more friction/heat, the more friction/heat the more wear. not much you can do except change the laws of physics.

Thank you for the physics lesson Maybe you should look at all the pictures, they're not wearing faster on the outside, they're wearing unevenly.

Originally Posted by idlafie

Hmmmm....you didn't mention it in your original post so I decided to check your profile to see what year your car was....97 eh? I was going to say it might have been due to possible overtightening, or uneven tightening of the lug nuts in relations to the rotor..(clamping force of brake rotor/wheels/rims to hub uneven possibly)...but that wouldn't really apply if you had a five lug hub in comparison to a four lug hub. Then it dawned on me that it's possible that the bearings on the rear hubs may be worn or shot. Have you inspected them lately??
I don't think the problem is with your calipers as you mentioned that the pads you've installed have worn the same on both rear sides. But then again I could be wrong. The pads in the stock rear calipers kinda float within the clamping portion of the caliper. Bout the only thing I can think that would affect that floating action would be either worn caliper pins or sticking/binding caliper pins. When you swapped the brake pads out on the rear the last time you serviced the brakes, did you clean & re-lubricate the caliper sliding pins? Are the caliper sliding pin boots still in good shap?? Other than that, about the only thing I can think of is either air in the line, (but you would notice that), OR maybe a stuck/misaligned E-brake cable or cable binding in the E-brake system/assembly. You might want to check those out too.
Good luck trying to figure this one out...it's gonna be a doozy...And when you do, let us know so we know what to expect in the future. Anyhow, hope this helps...

I regreased the pins on one of the sides, still the same uneven wear. As for the bearings, I was planning on taking the rear shield off (man it looks dumb when the front is gone) but I couldn't get the wheel bearing and flange seperated from the axle housing. The bearing itself operated smoothly but the flange was what was stuck. I'm hoping that one of my mechanic friends has the right gauges so I can measure the axial end play, but I think it will be ok since there is no wobbling in the rear that I can tell. The parking brake isn't causing the pads to bind up and works fine so I don't think that isn't it either.

Not sure if this explination will make sense but here goes anyway. I noticed yesterday when I was putting the calipers back on that when I had them lined up (the outside of the caliper flush against the pad) and I started tightening the pin bolts I could feel the caliper pull up. I'm not really sure what would cause this since the pins themselves look fine.

[idlafie]

Originally Posted by eng_man

Thank you for the physics lesson Maybe you should look at all the pictures, they're not wearing faster on the outside, they're wearing unevenly. I regreased the pins on one of the sides, still the same uneven wear. As for the bearings, I was planning on taking the rear shield off (man it looks dumb when the front is gone) but I couldn't get the wheel bearing and flange seperated from the axle housing. The bearing itself operated smoothly but the flange was what was stuck. I'm hoping that one of my mechanic friends has the right gauges so I can measure the axial end play, but I think it will be ok since there is no wobbling in the rear that I can tell. The parking brake isn't causing the pads to bind up and works fine so I don't think that isn't it either.

Not sure if this explination will make sense but here goes anyway. I noticed yesterday when I was putting the calipers back on that when I had them lined up (the outside of the caliper flush against the pad) and I started tightening the pin bolts I could feel the caliper pull up. I'm not really sure what would cause this since the pins themselves look fine.

Yeah...kinda makes sense....only thing I can thing that could cause that are 1). pins are slightly bent...possibly from heat & overtorque'ing or 2). threads inside the caliper are slightly stripped...one or two threads could have been cross threaded. I had a problem with my rear brakes last time I swapped them out...see attached picture....inside brake pad wore unevenly. I'm thinking it may be the caliper but I won't know for sure till I do another future rear brake job. If the future brake job still shows the same uneven wear, then I'm just gonna swap out the calipers & see if that fixes the problem. Only time will tell.
Anyhow, good luck with figuring out what's causing your problem....
ID
95 SE

[AKA Ryan]

Some people might know this some might not, but the pistons only back the pads off of the rotor a tiny bit to allow spin. If you've done a break job you know what I'm talking about. Anyway, sometimes the piston wont retract and will keep minor contact. And pad wear like yours happens with dual piston calipers and one piston keeps contact. But since it's the same on both sides, it would be wierd to be just coincidence. So I dunno.

[thx247]

It makes sense that the rotor is worn like that on both sides. If the rotor is leaning out (relative to the caliper) then its going to wear more on the side its leaning towards.

Check the bearing runout, and then check the slider pins on the caliper. Besides the rotor not sitting on the hub perfectly flat there is little else it can be...well maybe a piston thats not centered but I've never disassembled a 240 caliper.