What could have caused 1 brake pad to wear down to metal while my other 3 pads are ~50% used?

Question

I just paid $400 to replace the front brake pads and rotors on a 2011 Honda Pilot. Here is what the 4 brake pads look like: 3 are in great shape--maybe 50% usage?--and 1 is down to the metal, and I had metal-on metal contact to my rotor. The metal-on-metal pad was on the inside of the rotor--I think on the passenger side.

Here are the 4 pads:

A closeup of the metal-on-metal one:

2 good pads:

The 4 pads stacked together: the bare one is the 3rd one down, with no pad surface left:

Regular used rotor surface:

And the rotor rubbing metal-on-metal on the bad pad (for only 1 or 2 days):

What would cause only 1 brake pad to do this? All I can think is that maybe the last time I paid to have my brake pads replaced, the shop literally just forgot to replace one of the 4 pads, and so it started out already half-used.

See also:

1. Replaced brake pads - one pad was full, the other was gone. Brakes now very hot after driving

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Note: I compressed all images above to the required < 2 MB each by using jpegoptim at the command-line in Linux Ubuntu, like this:

cd path/to/folder_of_images
Compress all jpeg images to <= 1900 KB
jpegoptim --size=1900k *.jpg

Answer 1

It's must likely down to siezed slide pins, if it's a sliding caliper setup (more likely), or a siezed piston if it's a dual piston caliper.

If it's the slide pins, it's a fairly easy fix - extract the pins (which can be more or less difficult depending on how stuck they are!), clean them up, clean up the holes they slide in, re-grease and reassemble with new gaiters (the little rubber boots that stop dirt getting in - chances are these will have split, which is a common cause of this problem). Last time I did this, at the same time as doing the pads, it only added half an hour or so to the time taken.

A stuck caliper can also be freed off, but is liable to stick again, so in that case it might be better to have them replaced or refurbished.

Did you ask the mechanic who changed them about it? They'd have had to do something to free it, otherwise they wouldn't have been able to fit the new pads in!

If they didn't sort it properly, get it fixed ASAP, as not only will the replacement be sticking too, and so wearing out, but your brakes will be dragging on that side as well.

Answer 2

A couple of typical causes for this are:

1. Binding of the calipers in the caliper brackets. Often caused by messed up slider pins.

2. Stuck caliper pistons on one side of the caliper.

Answer 3

The other answers discuss the caliper mechanisms (pistons, slide pins) being stuck.

There is one more possibility - low quality brake pad that at some point became spliced into a metal part and a friction material part. The remains of the friction material had simply fallen off.

p.s. while you are at it, check the rear pads and rotors.

If a mechanic does a substandard work or sources low quality parts, one can reasonably expect failures at the other points he touched.

Answer 4

They replaced all pads.

It's extremely unlikely that they would have failed to replace one pad. Due to the way pads are replaced, you have to undo a set of hooks, clips and pins to release the 2 pads, and then, they slide out together. It's no more work to do both than 1.

Especially if only the pads are being exchanged, and the rotors are not being turned.

Speaking of that.

Rotors should be resurfaced when replacing pads

When changing pads, it is very easy to inspect the outer rotor surface. But the inner surface is up against a splash guard, so it can't be visibly inspected without removing it. Removing the rotor is a minor chore because it involves removing the caliper - just a couple of bolts and hang it by a coat hanger so you don't have to disconnect the hydraulic line... but I could see a shop not wanting to bother.

So they may have missed hidden damage on that rotor.

As you can see from the other 3 surfaces, rotor surfaces do wear somewhat, and the rotor should be re-surfaced with every pad change. This is called "turning a rotor", and many garages and auto parts stores have a machine in the corner which does that job alone. When I get it done at the friendly neighborhood O'Reilly's, they charge me $15-25 per rotor.

A lot of garages won't bother turning rotors, because most replacement rotors cost about what turning does. But your rotors aren't. I can certainly see you balking at $200 to replace rotors!

My theory

I agree with others that this is likely the caliper failing to float freely left and right, causing excessive pressure on the one pad.

However if your pads hadn't been turned at your previous brake service, perhaps the rotors were not inspected on the inside. Perhaps that rotor had surface damage which caused it to chew up the pad prematurely. If the rotor had been turned, this defect would have been caught.

Anyway, while I agree with the "make sure the caliper can float freely" advice -- my additional advice here is to have rotors turned everytime you replace pads. Since your rotors are expensive, pick a garage that does turn rotors.

And have common sense: if your brake action suggests a warped rotor, turning won't necessarily fix that, and play it safe with a new rotor. And if the rust is bad and is starting to affect balance or the cooling passages, that too needs to go.