Brand new rotor grinding/uneven wear

[Mason]

Hey all,

I just replaced all the rotors and pads in my 03 Acura CL. The rear driver’s side had been grinding since I got the car, so I removed the wheel to take a look and found nothing odd on either the rotor and the pads. Still, I had already bought new pads and rotors because it needed to be done regardless, so I went ahead and replaced them. That was last night, and already it’s back to making the same grinding noise, only now there are clear signs of uneven wear. The rotor has a strip going all the way around the outer edge about an inch thick that’s a different color than the rest of the rotor surface (see pics). The pads also show uneven wearing with a different colored strip along the outer edge of the pad that lines up with the strip on the rotor. Just to be clear, I have turned the wheel hub without the rotor installed and with it- no grinding at all. Only grinds after installing the pads.

The fronts don’t do it at all, and I haven’t gotten down and dirty in the rear passenger side yet but I can see through the wheel that the rotor has the same strip as the one I just described, although as far as I know it doesn’t grind like the driver’s side. When installing I hit the rotors with brake clean to take off that rust preventing film it comes with from the manufacturer, but in my hurry I didn’t think to spray the back side so I only did the fronts. I didn’t wipe it with a rag either. I can’t imagine this is the cause but I can’t think of anything else I didn’t do right. I’ve also heard something about lubing the caliper pins so they don’t seize and keep the pads constantly compressed. I don’t think this is my problem either because the pads grind as soon as I place them into the support bracket before even installing the caliper. Any ideas?

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Topic

[Terry Fojas IV]

Dismount both rear wheel and observe and compare for bents or uneven or improper mounting of break accessories. Make some measurements. Or find a way(u need extra eye) to observe for uneven compression of caliper when pressing the break pedal. Or find an exploded view of break assembly from manual and see if everything is correctly installed. Maybe the previous owner added an extra sheet of metal padding with the break pad.

[Mike]

The steps that you think are insignificant are actually important to prevent noise and allow the brakes to work properly.
The gentle scraping sound when the rotor is turned while the pads are against them is a normal noise
BUT
your brake pad is obviously not pressing fully against the rotor.
There should not be a constant scraping sound from the brakes when the car is driven and the brakes are not applied (obviously).
The most frequent cause of uneven pad contact is sliding caliper pins lacking proper silicone brake lube.
Lack lubricant can cause the pads to remain against the pad–making a constant scraping sound.

Your Acura’s caliper pins consist of 2 separate parts: A threaded bolt and the cylindrical sliding part that the bolt threads into.
I suspect that what you thought are the caliper pins are actually those threaded caliper bolts.

The caliper does not slide on the bolt.
The bolt just holds the caliper on to the sliding part, which mounts into the caliper bracket.
This sliding part is covered by an accordion like rubber boot to keep dirt and water out.
This part is what needs brake lube to allow the caliper to actually slide the way it should.

If that’s unclear look here at part #14.
This is what slides.
https://www.acurapartsworld.com/auto-parts/2003/acura/cl-coupe/prem-trim/5-speed-automatic-engine/chassis-cat/rear-brake-scat

All other types of greases/ lubricants create problems because they swell the rubber grommets that allow the calipers to slide.

The pad might also be cocked in the bracket due to accumulated dirt or rust on the caliper bracket clips or beneath the clips.
Sometimes a groove wears into the clips, necessitating replacement.
They’re fairly inexpensive and can be bought from places like Rockauto and Amazon if your local parts store doesn’t have them.

You can use a piece of emery cloth to lightly sand the pad surface to remove any rotor oil residue that they scraped off the new rotor.
Use the brake cleaner to get the rest of the rotor oil off the rotors.
Applying a touch of anti-seize on the caliper ears, hub face and hub screws is advised.

Your rear caliper is also supposed to have an anti-rattle clip that sits in the hole in the top of the caliper. No need to lubricate this clip.

Once in a rare while pads are sloppily machined and the “ears” are just slightly too tight for the bracket but most often it’s dirt / rust on or under the clips causing the issue..

See here for ETCG video with more details.
These Honda brakes are very similar to yours.
The main difference is that yours have parking brake shoes, rather than a ratching caliper piston parking brake.

At 7 minutes he shows cleaning/lubing the slides with silicone brake lube.
At 23 minutes he covers the pad lube points–which require anti-seize compound..

[Author]

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