2017~2025 CX-5 Original Front Brakes, Outside Pads No Wear, Inside Finished?

[Davidiot]

I first noticed a cyclic rubbing/dragging sound seemingly coming from one or the other of my front wheels while driving with the radio off one day. The rub seemed to be consistent with each revolution of a wheel (the frequency of the rubbing sound quickly increasing with the vehicle’s speed). This was soon followed by some aggressive steering-wheel shaking during braking, making the culprit much more certain. Only 24,000 miles since I bought my CX-5 brand-new, I wasn’t expecting to need brakes yet, much less new rotors .

Since the first 6,000 miles, though, my car’s really only seen town miles, almost exclusively stop & go, so I had to consider that perhaps this mileage could be normal, given my circumstances? Not sure how I managed to warp (at least one of the) rotors without ever hearing any warning sounds from brake wear indicators; but might that be because Mazda doesn’t install them?

I went ahead and bought new front rotors and a set of brake pads for all 4 wheels, and borrowed a pair of jack stands and a couple of torque wrenches so I could get started on doing the work myself. Having only two jack stands and the scissor jack from my trunk, I haven’t been able to take a look at the rear brakes yet; but I did pull off the fronts earlier today.

I am in SHOCK at what I found. Wtf, Mazda?

The inside pads on both the front left and front right wheels are worn down completely; while the outside pads are still almost as fat as the brand new replacements I just bought. How could this have happened with factory-installed brakes? What other parts am I now looking at having to replace to make sure the same thing doesn’t happen again to my new rotors and pads?

 

[HyFlyer]

... Yes, I’d like to know how to prevent that; but I’d also like to know how they got that way in the first place. ...

I'll get back to you when I have time to type more.

 

[Jmaz]

The threaded hole in the rotor typically takes a M8-1.25 bolt (8mm diameter with 1.25mm thread pitch)to act as a "jack screw" to loosen the rotor.

 

[Jmaz]

Your entire post was excellent information — Thank you!
Re: 1 — guy at the parts store told me they should pop back out if lubed correctly — is that wrong? Should they instead automatically retract if pulled out and released?
Re: 2 — I did that! Got my lefty-loosy, righty-tighty backwards when attempting to loosen the bolt from the opposite side (initially got more resistance than expected; mistakenly thought I’d got it backwards, and then cranked too hard the other way). Doh!

The guy at the parts store (always a source of trusted professional wisdom ---sarc) was half right in the sense that there's sufficient grease if the pins pop out and aren't binding. But the other half is that the air still needs to be burped out by lifting the edge of the accordion boot. You do not want the trapped air continually forcing the caliper (and pad) against the rotor, even if it's with a light pressure compared to braking.

 

[CrazyHippie]

You know in the manual when it says to lubricate your caliper pins? This is why it says that.

Yep, those calipers are stuck. I'd replace them along with new pads and rotors. These days replacing calipers is better than trying to re-build them. Otherwise, this will continue to drive you nuts!

 

[gazelle]

Let me just put this here to assure you that it happens regardless of whether it’s serviced by the dealer or by yourself:

- These are my rear brake pads on a 2016 with the same issue, if you go through that thread you'll see that it's a wide-spread issue.

- And the same story on a 2021: Rear pads changed 2nd time at 23k?!

Both cars serviced by the dealer, twice a year.

 

[Davidiot]

I believe it's the same size/thread pitch as the spare tire hold down bolt IIRC

Ah! That got me excited; I just ran outside in the dark to try it out. I’d stashed both front wheels atop the compartment holding that hold-down bolt, so had to shuck the tires first. Alas, it didn’t work. Could only barely get the bolt started turning on both rotors before it jammed up; trying each rotor from both inside and out— same as I encountered when attempting to pop the rotors off with the variously pitched 8mm bolts I’d tried using out of one of my networking/AV hardware install tool kits.

It didn’t occur to me that perhaps the issue was simply excess corrosion until after I’d put the hold down bolt back and loaded my wheels back into the boot, and that I should’ve tried it with the new rotor. Well, I wasn’t going to dig the bolt from the car back out again, but I did dig out my toolkit, and — well, surprise! The 8mm x 1.25mm (verified by micrometer) worked just fine on the new rotor.

In any case; I would up just banging the heck out of the rotors with a hammer and did finally get them off. I’ll definitely be using anti-seize on the hub when I put the new rotors on; and probably a bit more where the wheel will make contact with the hub of the rotor. Thanks!

 

[Davidiot]

The guy at the parts store (always a source of trusted professional wisdom ---sarc)

. You do not want the trapped air continually forcing the caliper (and pad) against the rotor, even if it's with a light pressure compared to braking.

This makes sense; thank you. I’ve been dragging my feet putting everything back together (partly because of health issues, partly because I’m not yet convinced I know everything I’m supposed to know yet) …

Here’s something I’m still fuzzy on: I’ve read there’s supposed to be a 1mm gap between the surface of the pads and the rotors when the brake pedal is released. I can’t figure out what mechanism backs the pads away from the rotors when brake pressure is released. The pads seem to have some wiggle room inside their clips (inward and outward, with respect to the rotor) with the calipers stationary at rest. My understanding is pressing on the brakes extends the pistons, pushing the inside pads snug against their rotors; and that continued extension of the pistons from that point pushes the caliper assemblies themselves toward the engine, which entirely pulls the outside pads snug against their rotors, too.

If I release the brakes, the pistons should retract, and thus they should stop pushing up against the inner pads. What mechanism makes the whole caliper assembly recenter itself? What further mechanism pulls both the inside and outside pads away from the rotor?

I’ve watched animations of the whole process, and the mechanics of braking make sense, but I don’t see how the pads are pulled away from the rotors. I’ve seen other arrangements where springs are installed between the sets of pads on either side of a rotor that push them apart unless the piston and caliper assembly pinch them together — but I see nothing similar in my Mazda.

When I temporarily reinstalled my old brakes and put the wheels back on so I could make a few short trips (except putting the like-new pads on the inside and used up ones on the outside) — I had cleaned and lubricated the slide pins, which moved well; so I DIDN’T experience the terrible steering wheel shaking during braking I had prior. But I could still hear loudly, inside the car, the dragging of my pads whenever the wheels turned, even when completely off the brake pedal — so much so that my car didn’t even accelerate when rolling down a steep hill.

* I also don’t see any brake wear indicators (mechanical or otherwise) that would have been included with my factory installed brakes; nor do I see any included with the hardware of my new replacement brakes … should I ? But that’s a whole other issue.

 

[Davidiot]

Yep, those calipers are stuck. I'd replace them along with new pads and rotors.

You’d replace the calipers? Even if I’ve removed the slide pins and boots; thoroughly cleaned the inside of the slide pin housings, cleaned, polished, and lubed the slide pins (replacing the one which I accidentally broke a bolt head off in), and fresh boots?

Or are you suggesting replacing the pistons themselves (instead or as well)? Because both of those are well beyond my budget.

 

[HyFlyer]

... Here’s something I’m still fuzzy on: I’ve read there’s supposed to be a 1mm gap between the surface of the pads and the rotors when the brake pedal is released. ...

No gap on any disk brake I've ever seen. On a drum brake .. sure, but not on a disk.

 

[Davidiot]

Let me just put this here to assure you that it happens regardless of whether it’s serviced by the dealer or by yourself: […]
Both cars serviced by the dealer, twice a year.

My car’s brakes had never been serviced at all — they wore that way presumably straight from the factory. If my dealer ever did check them during my first oil change, they never said anything about how bizarrely my brakes were wearing.

Thanks for the links — checking them out now.

 

[Davidiot]

No gap on any disk brake I've ever seen. On a drum brake .. sure, but not on a disk.

Really? So they just stay snugged up against the rotors all the time? That doesn’t cause excess wear, heat, or drag?

 

[HyFlyer]

@Davidiot , my SIL bought a 1998 bmw z3 this past summer. He was having an issue with the front brakes dragging. The car was rarely used and mostly sat in a garage by the previous owner who installed new pads and rotors. To solve the sticking caliper pistons, I had my SIL sit in the car and with one brake caliper off at a time, he slowly pumped the brake pedal several times as I watched the piston come out several mm's (about a full pad thickness). Then I would squeeze it back in. Repeat about a dozen times working the piston out and in like that. Same for the other side.

He hasn't had a problem since.

 

[Davidiot]

[…] he slowly pumped the brake pedal several times as I watched the piston come out several mm's (about a full pad thickness). Then I would squeeze it back in.

I’d been planning to fully pop the pistons out a bit before collapsing them again to put the new rotors and pads back on; in order to get a good look at the piston boots, look for damage, clean them up, and lube them. Did you noticed a difference in how they came out when your SIL worked his brakes; and/or a change in the difficulty of compressing the pistons again between the first few cycles and the twelfth?

 

[HyFlyer]

I’d been planning to fully pop the pistons out a bit before collapsing them again to put the new rotors and pads back on; in order to get a good look at the piston boots, look for damage, clean them up, and lube them. Did you noticed a difference in how they came out when your SIL worked his brakes; and/or a change in the difficulty of compressing the pistons again between the first few cycles and the twelfth?

Oh yes.BIG difference. The pistons were very difficult to push in at first and were progressively less resistance each cycle.

 

[CrazyHippie]

You’d replace the calipers? Even if I’ve removed the slide pins and boots; thoroughly cleaned the inside of the slide pin housings, cleaned, polished, and lubed the slide pins (replacing the one which I accidentally broke a bolt head off in), and fresh boots?

Or are you suggesting replacing the pistons themselves (instead or as well)? Because both of those are well beyond my budget.

Hi! If you're budget-constrained, replacing the pistons may be a good compromise. If you're into the job this far, at least pull them and check for scoring and remove any corrosion. In my experience, rebuilding a caliper is only a temporary fix once they stick and premature pad failure with uneven wear may continue. Hope that your luck is better!

 

[Jmaz]

This makes sense; thank you. I’ve been dragging my feet putting everything back together (partly because of health issues, partly because I’m not yet convinced I know everything I’m supposed to know yet) …

Here’s something I’m still fuzzy on: I’ve read there’s supposed to be a 1mm gap between the surface of the pads and the rotors when the brake pedal is released. I can’t figure out what mechanism backs the pads away from the rotors when brake pressure is released. The pads seem to have some wiggle room inside their clips (inward and outward, with respect to the rotor) with the calipers stationary at rest. My understanding is pressing on the brakes extends the pistons, pushing the inside pads snug against their rotors; and that continued extension of the pistons from that point pushes the caliper assemblies themselves toward the engine, which entirely pulls the outside pads snug against their rotors, too.

If I release the brakes, the pistons should retract, and thus they should stop pushing up against the inner pads. What mechanism makes the whole caliper assembly recenter itself? What further mechanism pulls both the inside and outside pads away from the rotor?

I’ve watched animations of the whole process, and the mechanics of braking make sense, but I don’t see how the pads are pulled away from the rotors. I’ve seen other arrangements where springs are installed between the sets of pads on either side of a rotor that push them apart unless the piston and caliper assembly pinch them together — but I see nothing similar in my Mazda.

When I temporarily reinstalled my old brakes and put the wheels back on so I could make a few short trips (except putting the like-new pads on the inside and used up ones on the outside) — I had cleaned and lubricated the slide pins, which moved well; so I DIDN’T experience the terrible steering wheel shaking during braking I had prior. But I could still hear loudly, inside the car, the dragging of my pads whenever the wheels turned, even when completely off the brake pedal — so much so that my car didn’t even accelerate when rolling down a steep hill.

* I also don’t see any brake wear indicators (mechanical or otherwise) that would have been included with my factory installed brakes; nor do I see any included with the hardware of my new replacement brakes … should I ? But that’s a whole other issue.

To answer your question, it's the piston seal (in the bore) that retracts the piston. The seal has a square cross section (as opposed to a round cross section in an o-ring) that distorts when the piston extends and then reverts to it's square shape pulling the piston back (it's only a tiny distance) when brake pressure is released. It lacks the retraction force that a spring would provide so a sticking piston (as mentioned in above posts by some members) could be continually forcing the pad against the rotor. It's normal for there to be essentially no pad to rotor clearance with the brakes released as long as they aren't dragging. It'd be on the order of thousandths of an inch. If curious, a person could check with a feeler gage. Have you jacked the car up and turned the tires to check which brakes are dragging.
You have to remember that the calipers are the lowest location in the system and moisture (being heavier than brake fluid) and dirt from seal wear , accumulate there due to gravity and cause corrosion. That's why it's good to flush the brakes every so often.