I really need some help guys. I just changed my brake pads to Stoptech brand pads at all four corners. I did not reuse the OEM shims (still have them though). Anyway, I did the bedding in procedure and noticed the next day that my rear driver side rotor was wearing funny. It's like it appears that the pad is not making full contact with the rotor. The upper part looks nice and shiny, but the lower half of the rotor has that rusted look you get when you leave the car parked over night. I have no idea how this can be happening. Please Help.

P.S. I also notice that initially i'll get some brake squeal coming from the front when I just start driving and it'll go away. But when it happens, it's very loud. The Stoptech pads came with their own shims and no brake pad grease. Should I put the OEM shims on the Stoptech pads. Also my shims were 2 pieces OEM, but the new ones are only 1 piece. And they gave me wear indicators on both driver and passenger side rear pads.

 

I would check and make sure the caliper is sliding properly on the pins. It should slide easily without binding.

Most problems with sliding type calipers is the slide pins get gucked up when the rubber seal fails and crap gets into the outer sleeve

Usually this can be remedied by cleaning out the slide and the pins and lubricating them with high temp ceramic or silicone based brake grease

 

I'll check that out. So do I just turn it counter-clockwise then to make it extend?

 

That's the piston...the slide pins allow the caliper to slide in and out when the piston pushes on the other side.

 

This is what it looks like. I took off the pads and checked the slide pins. Unscrewed both bolts and they move smoothly in and out. I even rotated the piston a 1/4 turn and inspected the rubber boot. No imperfections.

 

Just drive it for a while and it will be OK...as long as the slides are OK it is just likely a little bit of a taper on the pads that will wear away. Check it out after 100 miles or so..it will likely not be a problem

 

OK, thanks for the assistance and quick responses. Appreciate it.

 

^I don't agree and here's why. The force the pistons exert on the pads will force the pads against the calipers regardless. If pads have some taper from wear, the pistons will tilt and press them against the rotor anyway. These are new pads, there should be minimal, and more likely no taper.

You have a problem of some sort. Understand you turned the piston, tried the slides, but you just haven't come upon the real problem (yet). Stuck piston, caliper pin problems, crimped/blocked brake line, didn't bleed that line well enough, something. There's no way that's normal or acceptable and certainly not after breaking in new pads. Start and go over everything again, proceed carefully and you'll find it.

 

Another thing to check out, Make sure the bump/nipple on the back of the pad on the piston side, is in one of the four grooves of the piston. Did you turn the pistons all the way in?

9K and Dan, could it be that the rotors are really wore out on the inside. He didn't say new rotors.

 

Tankerg, good point about checking the bump on the pad, not sure what that would do actually, but also doubt aftermarket pads have them, however your mention of uneven worn rotors (you removed it?) is a thought. If the rotor is the cause the pads will bed in after a fashion to worn rotors, but not such a good practice esp. if the rotor is that bad.

 

I did, I guided it over that bump on the pad. I did rotate the piston all the way back and inspect the sleeve. I cleaned out any gunk I found with brake cleaner and some paper towels. I even checked the new inner pad and there is even consistent wear on it. I have no clue as to why the outer pad is not making even contact with the rotor. It makes no sense since what holds it in place does not move.

I did not change the rotors though, so I never took them off to inspect them. I didn't think I had to because there was no braking vibrations when I would brake.

The sad thing is, is that I really didn't have to change my rear pads. The ones that were wearing were my front pads, and it was majorly the front passenger pads at that. I don't know why my front driver side didn't have wear indicators too, but that's neither here nor there. I did not bleed the system because I didn't think I had to since I was only swapping in new pads.

 

One question. Is there a way to manually extend the piston? I know rotating it clockwise compresses it, how would I extend it so as to make sure to extends properly?

 

How many street miles/track days on the rotors?

You don't have to take the rotors off to check them (at least) for cavitation. Take a *short* straight edge or card and hold it against the working surface and shine a flashlight behind it to easily see the cavitation. Go inside the outer edge, as almost for sure there will be a ridge there that needs filing off anyway ( you did file it off, yes?) and you can't get a good indication if the card is up on the edge. An edge is not killer, you can file it away, but excessive or grooved or sloped in/out rotor surface would not be so good. Beside rotors can be bought for little money if you're not buying racing type. Why start putting on uneven wear on new pads by using old worn rotors?

Ideally, bleeding should be done whenever you fully compress the pistons, and if you have not done bleeding within the last year, it would be good anyway. BUT! Where you ARE having problems, flushing the system would be advisable, not just a quick bleed. It a bit more of a pain, but when it comes to safety (and finding the problem) you need to eliminate possibles one by one.

Sure you can extend the piston if you are really careful. Put suitable sized wood blocks where the pads would be about the thickness of the pad backing metal (or use pads with no pad material left) , then press the brake pedal gently until the piston compresses against the block. That's about as far as you'd want to expand them without possible piston removal in mind.

 

Honestly, with how inexpensive it is to replace the sliding pin and assorted other bits, I would highly recommend that as step one, if the car has a decent amount of miles on it already.

Is this only happening on the one side of the rear axle, or is it happening on both sides of the rear axle? Seems to be only on the one wheel. Take everything there back apart, and reinstall it. Either something wasn't placed correctly, or it has a failure that is just beginning to show.

Was the wear like on the worn brake pads you took off of that wheel?
Was it even, or was it uneven?
If it was evenly worn, then its your work that has introduced the problem.

BC.

 

This is strictly a street driven car with some occasional spirited driving. I have my front brake piston compression tool, so I can use that to stop the piston from over extending. i'll also take a pic of the new pad, just to make sure that there is no uneven imperfections. Thanks for the help and quick responses.

 

I just checked the pads that I replaced and they are all evenly worn. I have 61k miles on the car, bought it with just 15k. First pads I am changing. The passenger side rear is fine, I'll take it apart again and get a bleeder kit to bleed the line. I'm still not sure how this is even possible since the outer bad is on a fixed bracket with no movement. There has to be some uneven pressure. it's hard to picture there only being pressure on the top part of the pad that's some how causing it to be angled.

 

You were totally correct. I did not file down that edge and that's what's causing the uneven surface contact. I saw that there are resurfacing pads I can get at AutoZone. Should I use those with a drill to file the edge down, or is there something more suitable that can file it down correctly?

 

It's often rust and metal. I have used a drill and grinder wheel to get it down. You could also just take the rotor off and get it resurfaced at Autozone.

 

Looks like I might have to go with the new rotors route. I only have one car. Sadly I might be trading my 8 in for something a little bit more practical but still fun. I was thinking a WRX. So I'm not really looking for the more expensive higher level performance focused rotors. What do you think of Bosch Premium Quietcast rotors? They seem pretty good.

 

$41 shipped on Amazon? Why not.

 

all aboard the train ....

 

you can get rebuilt rear calipers that include the mounting bracket, pin hardware, pad hardware, etc. fairly cheap on rockauto.com

once you turn in your old calipers and get the core charge refunded they'r less than some people sell used calipers only on the forum ...

 

Honestly, if you're thinking of getting rid of the car soon, just buy whatever is cheapest for the rear.

BC.

 

Actually, those might be the cheaper rotors, lol. I'm still debating though. It's hard thinking about getting rid of my 8 . I so love the car, and I'll lose so much, even though I'm going to a nice performance car. I lose the better interior, that amazingly sweet shifter, the rotary engine, the awesome handling, I have the Grand Touring with cold weather package; so no more heated seats and mirrors. Plus it's hard to find a reasonably priced less then 70k miles Subaru WRX. People really drive those cars. Hopefully I can hold out and eventually just get a second car instead . Worst case, I trade her in, and eventually years later when I'm better off, I'll buy a used 8 or hopefully if Mazda has any future rotary variants. I really wished they would push for the hydrogen powered cars. The rotary is perfect for it. A lil more research and I know they could probably bump up the power gained since hydrogen burns better and you get more bang for your buck.

 

Is it wearing down on the outside of the pads? Is there like a little lip on it? Cuz from the pic, isee the rotor a bit small if it's the sports package. I ran into the same problem when i got mine, i changed the pads and it was uneven wear, turned out the previous owner didn't want to spend a few extra bucks to get the right rotor. Might check that out as well.