How can a brake pad fail like this?

[open_circuit]

While running an errand this morning, my wife heard a terrible sound from the rear passenger tire on her van. She said she thought the wheel was falling off. She brought the van home where I pulled the rear tire and brake caliper and had a look. The inboard brake pad on the rear passenger tire was worn down completely and had worked itself out of the seating / guide slides. Her van only has 47k miles and these are original brake pads from when we bought the van new off the lot. The other brake pad from the same caliper is about half worn, as were both pads on the rear driver wheel. I replaced all of the rear pads today, and inspected the fronts. The fronts were all worn evenly and have about 40-50% remaining, so I did not yet replace them.

I am concerned about how a single pad in a caliper can wear completely down like this while the opposite pad does not. The pad that caused the problem is the pad that the piston pushes on.

Any ideas? Is there something else I should be checking for or replacing that I didn't notice? Upon seeing the pad, I thought I would have to replace the rotor also, but the rotor doesn't seem obviously badly scored or warped, so I'm thinking I'll just leave it.

Right now my best guess is that the worn pad was defective and a big chunk of it disintegrated suddenly at some point. All other theories I can think of involving something sticking in the caliper bring me back around to "if the caliper wasn't moving correctly, why is the mating pad worn about halfway instead of not worn at all or worn all the way down?"

Photos below show all 4 rear pads. The pads with the springs on top are the inboard pads. Ignore the weird circle on the bad pad -- that is from the C clamp I used to try to compress the piston. I used the bad pad as a load spreader.

https://i.imgur.com/BqL8Ural.jpg

https://i.imgur.com/EkuOfcsl.jpg

https://i.imgur.com/05pFsPFl.jpg

[RockyMtRebel]

The caliper might be shot, happened to my Jeep. In my case after pressing the brake pedal and letting go the piston was not retracting as it should. If your wife’s brakes have multiple pistons on the caliper maybe one of them is not doing it’s job causing the pad to wear in that spot

[open_circuit]

Just one big piston

It retracted ok with the tool. Couldn't compress with a c clamp because this type of piston needs to be rotated while it is compressed. Had to rent the tool with matching die from the FLAPS

[Tom]

I had an F150 and that same thing happened on the front passenger. Since I had done the brake job I assumed I did not seat the pads in the bracket correctly. I figured they weren't seated and wore because they were constantly rubbing. You've made me second guess that now.

Have the pads been replaced previously?

[open_circuit]

No. These pads are the originals from the factory. We bought the van new and have been the only owners. Basically it has just had oil changes, wipers, and new tires since we bought it

[Brian]

I would venture a guess that the pad became unbonded suddenly rather than being rapidly consumed, and was ejected from the brake assembly. In the pics of the bad pad there seems to be a shiny or scuffed area on the metal plate along the missing pad. Might be from the pad exiting the steel plate intact. Also I would think wearing through an entire pad would leave the rotor, at least on that side, with some level of uneven wear. Just my CSI .02 :)

[open_circuit]

I agree about the rotor. It's hard to see the backside and I didn't remove it yet today. I'll pull it back off Saturday when I have more time. Probably will end up replacing it.

[Hypoid]

Her van only has 47k miles and these are original brake pads from when we bought the van new off the lot.Is this not covered by warranty?

Year/make/model might be useful.

[Hypoid]

All other theories I can think of involving something sticking in the caliper bring me back around to "if the caliper wasn't moving correctly, why is the mating pad worn about halfway instead of not worn at all or worn all the way down?"That, actually, is common wear for a "sticking" caliper.

[FINOCJ]

My first thought was sticky caliper piston as well, but when I looked again on the large screen at home, I am kind of thinking Brian might be on to something: Can you tell if it looks like the pad unbonded from the backing material? Might just be a failure of that single pad....not good, but maybe better than a complete overhaul of the caliper etc.

[open_circuit]

Is this not covered by warranty?

Year/make/model might be useful.

2014 Mazda 5. I assume it is too old to be under warranty for this.

[open_circuit]

My first thought was sticky caliper piston as well, but when I looked again on the large screen at home, I am kind of thinking Brian might be on to something: Can you tell if it looks like the pad unbonded from the backing material? Might just be a failure of that single pad....not good, but maybe better than a complete overhaul of the caliper etc.

I wondered the same. It looks like there is a tiny bit of brake material left on the backer and it wore more in the back than the front. I might be interpreting what I am seeing wrong, but it looks like if the pad unbonded, it sheared a section off because what is left on the backer is textured and not completely flat.

[Java]

Wow, glad nothing bad happened from it! I think Brian nailed it, looks like just a defective pad. Having said that, if that was my wife's car I'd replace the caliper too just for my peace of mind.

[open_circuit]

Wow, glad nothing bad happened from it! I think Brian nailed it, looks like just a defective pad. Having said that, if that was my wife's car I'd replace the caliper too just for my peace of mind.

The calipers appear to be cheap ($40 or less), so I'm leaning towards just replacing the one caliper. I have a rotor on the way in the mail as well.

I haven't replaced a caliper before, but it seems like I'd just need to clamp the hydraulic line (vice grips?), disconnect the old caliper, connect the new one, and then unclamp the line, then bleed that brake line and top off fluid if needed? I shouldn't lose very much brake fluid in the process this way, and the risk of introducing air into the line should be low?

[newracer]

I vote for sticking caliper. You don't need to clamp the brake line, you won't lose much fluid. Plus since the vehicle is 6 years old I'd at least partially flush the system anyways.

[RockyMtRebel]

Correct, you don't need to clamp the line... you just unbolt the caliper and have it ready to remove and then unscrew the brake line from hard line (usually 12" or less from caliper) and move quickly to minimize the mess (but there will be some dripping of fluid obviously). Screw new calipers brake line into the main brake line (dripping will stop) and then bolt up the caliper. It's actually very easy job, did mine last year for the first time. Obviously you will then have to bleed your brakes.... I choose to gravity bleed because its easy as pie and really the best way to get all the air out, just takes an hour or so of time.

[open_circuit]

Correct, you don't need to clamp the line... you just unbolt the caliper and have it ready to remove and then unscrew the brake line from hard line (usually 12" or less from caliper) and move quickly to minimize the mess (but there will be some dripping of fluid obviously). Screw new calipers brake line into the main brake line (dripping will stop) and then bolt up the caliper. It's actually very easy job, did mine last year for the first time. Obviously you will then have to bleed your brakes.... I choose to gravity bleed because its easy as pie and really the best way to get all the air out, just takes an hour or so of time.

I have a self-bleed kit that makes it pretty easy to bleed by pumping the brakes. (https://www.amazon.com/Genesis-Person-Brake-Bleeder-Bottle/dp/B000W7F2GI?ref_=Oct_s9_apbd_oup_hd_bw_b13uBt&pf_rd_r=Q7M6D9MHXG546R0D1J31&pf_rd_p=a241c0e6-af8a-5b55-9b01-6d9a1c6feaf9&pf_rd_s=merchandised-search-10&pf_rd_t=BROWSE&pf_rd_i=15707321). It's just a bottle with a magnet glued to it and a length of flexible tubing to attach to the bleeder screw. Seems to have worked well on my Jeep and Subaru (though there are many more good places to stick the magnet on the Jeep!)

[newracer]

I put Speed Bleeders on all my vehicles to make bleeding extremely easy.