Right rear brake rubbing each rotation?
 

I’ve gone through a bit of troubleshooting already and I can’t figure this one out.

I’ve got a rubbing/grinding noise coming from my right rear wheel and I think it’s related to my brakes. It happens rhythmically, like there’s only one spot on the rotor where the brake pads are catching and locking up. The Miata in question is a 95

To start from the beginning:
I WAS experiencing a leaky passenger rear (right rear) caliper but I replaced both of the rear calipers and the brake pads all around. I get the car off the jack stands and go to test drive it and notice there’s a rubbing noise coming from my right rear wheel. I assume I’ve mis-adjusted the parking brake lever, so I get it back up on the stands and adjust both the right and left rear parking brake at the caliper (4mm allen key under the 14mm bolt). For both sides I did the same procedure; with the parking brake lever disengaged, tighten the 4mm adjuster until tight, then back off about 1/2 turn.

I go to test it and the right rear wheel is STILL rubbing.

I put the rear back on jack stands and run the car in the air, wheels on, right rear sticks and rubs (so much so that the wheel doesn’t rotate with an open diff). With the wheel off though, it DOESNT rub. This leads me to believe that my wheel or lug nuts are causing some distortion on the rotor, leading to the grinding.

The lug nuts are a little ratchet anyway (recently bought this car), and one of them is a flat seat locking lug nut, so I order and install a whole new set of 60 degree taper conical lug nuts (M12 x 1.5). Since I was breaking up the project anyway, I order fresh rotors to go with the fresh brake pads, just in case the rubbing is a rotor issue. I install the new rotors and proper lug nuts on all four corners. I reset my parking brake adjusters on the rear calipers. Yet when I go to test, lo and behold I’m STILL getting a rubbing on my right rear wheel every rotation.

What could be going on here? How can I troubleshoot this? Could my hub seat be lopsided and the rotor isn’t sitting flat?

TLDR:
Right rear brake is rubbing once per rotation after new caliper (rears only), new rotors (all around), and new brake pads (all around), and rear parking brakes have been adjusted.

I assume you've inspected and greased the slider pins for the rear calipers?

a pitted pin can cause it to not slide properly.
And a belt one can cause it to grab.

Also check wheel bearing play, if they're totally dead it can allow the hub to shift a little, altering the angle of the rotor with it.


Also check the rear brake adjustment, I cant remember what the "official" amount to back the screw off is, but I know that whenever I've done it it's always needed more than that to not drag the pads.


Also, when checking for pad rub, you dont need the car running.
just turn the wheel/rotor by hand. You'll be able to feel where and how much it rubs a LOT better.

That screams of a bent hub......take the wheel off and lock the rotor down with a few lug nuts, I betcha you'll see the rotor doing the hoola.

Hubs crack and fail dramatically on Miatas. Inspect it carefully.

I appreciate all the suggestions. I’ve done some work and I have some results to post.

RE: the slider pin on the brakes. Admittedly, I haven’t checked the slider pin but I will. The calipers are brand new though, so I doubt the slider pin is messed up.

RE: the parking brake adjuster, I’ve tried loosening it way up so the brakes are further apart and it doesn’t seem to help. I’ve also tried setting to factory spec (around 1/2 turn off from tight) and it still rubbed.

RE: the possibility of a bad hub or wheel bearing; I replaced the right rear hub.

It was a total pain in the ass to get the hub off, I had to borrow a compressor and buy an air hammer, but I was able to break everything free and put together a new hub, new rear wheel bearing, and new wheel seal. And it STILL rubs, ugh.

I took a short drive and recorded a video. Not going to lie, I’m pretty bummed that replacing the hub didn’t seem to have any affect on the issue, but it’s good to know I’ve got a fresh hub on that corner. Is it possible that the new wheel bearing is bad? How do I check for that? I’m assuming the wheel would be able to wobble a bit while mounted in the air. Anyone have any other ideas on what the issue could be?

Just covering the bases - you've thoroughly checked the tire to make sure there's nothing stuck in the tread, right?

Ninja edit to add - does this happen when the car is in the air and you spin the wheel?

Yes - it happens while the wheel is in the air. It also does not happen if I rotate the rotor/axle/hub in the air with the wheel dismounted.

Silly questions but did you make sure the wheel is mounted properly and if you spin the wheel while the car is in the air it looks trued?

I had a similar issue once where the bore of the wheel got stuck and gouged with the hub dust cap and when torqued the wheel was cockeyed a bit.

With the car in the air and the wheel on, does it still make the sound? At what position does it make the sound (1 o’clock, 6 o’clock ?). Have you inspected the wheel and wheel weights for damage? Maybe a cracked spoke?

@thebeerbaron yes - with the wheel on in the air, it makes the rubbing sound, once each rotation in the same spot. It's definitely the brake pads 'grabbing' the rotor and slowing the wheel, so I'm not sure what you mean by 1 o'clock, 6 o'clock I need to get out there and mark it to see if the spot rubbing stays the same if I rotate the wheel on the hubs. Perhaps more importantly though, I can't believe I didn't think about swapping the wheel from the rear left to see if the rubbing noise continues.

I will do a few tests and report back:

1. Mark rubbing point on wheel AND hub where it's rubbing, then dismount and re-mount the wheel rotated on the hub to see if it continues to rub on the same spot on the wheel, or on the same spot on the hub
2. Swap different wheel onto the right rear hub and see if the rubbing noise continues

Thanks for the suggestions guys!

Eh, confusing results to report back.

I did a few tests and I’m not sure how to interpret the results. I’ll post the tests I did and the results, then my interpretation.

Test 1: Mark rotor and mark wheel to see if brake pad is rubbing on the same spot on the wheel or the same spot on the hub/rotor assembly.

Results 1: Brake pads continued to rub on the same spot on the wheel, regardless of hub/rotor position.

Test 2: swap rear wheels to see if a bad wheel causes rubbing once swapped to the other side.

Results 2: right rear continues to rub when the left rear wheel is mounted. Argh.

Test 3 and 4 really started to mess with my head.

Test 3: remove right rear wheel, see if it spins freely.

Results 3: right rear hub does NOT spin very freely even with wheel removed. It doesn’t necessarily ‘stick’ and rub the same way as it does with the wheel mounted, but it’s sticking enough to not want to spin when the car is in gear on the stands (it’s an open diff, so the rear left IS spinning).

Test 4: unhook parking brake from right rear, see if that improves ability for hub to rotate.

Results 4: even with parking brake removed, there’s still some brake pad rubbing that’s keeping the rotor from spinning freely.

I also noticed that there seems to be more ‘play’ in the right rear caliper than in the left rear caliper. I’ll post a video of it happening in action, and videos of some of the tests above that I did.

Any ideas anyone? I actually have two Miatas, so I might try mounting two of the known good tires from my other Miata on the rear of the trouble Miata, see if that makes any difference. I’m really stumped on what might be the issue. Could it be a bad or warped rear caliper?

Try moving the rotors around and see is the issue follows the rotor.
Also, clean all mating surfaces with a wire brush.

Are you absolutely positive the rotors are perfectly true?

Any chance you’ve disturbed the caliper bracket mounting bolts? (The two 14mm head bolts that attach the bracket to the upright). Are they tight, and have you removed them recently?

I’m as confused as you are at this point, I gotta think some...

Check the CVs on the axle on that wheel. Also, does it stick with no rotor at all? That should determine if it’s in the axle/bearing or the brake assembly.

Well I might be the biggest idiot. The issue seems to be fixed now, and I think there were a couple things causing it.

What I think the main issue was: poor wheel clearance between the stainless steel braided brake line and the wheel weights. I think these were just barely catching and bending the line, causing a little bit of pressure in the line to compress the brake pads. To make matters worse though, I think the slider pins were catching just a little bit, causing the brake pads to stay engaged. When I removed the caliper, went over it with fresh brake lube, and re-installed it, I rotated the SS brake line to sit more inside the wheel. After re-install, there are no more issues with the brake pads catching.

But Dylan, what about the slow/no rotation even with the wheel off? Well like I said, I think the slider pins weren't totally smooth and so that was causing some sticking. In addition, with the open diff on the car, the good wheel was spinning just fine, and I'm guessing the diff just couldn't send enough torque to the right rear hub to rotate it. In any case now, the issue seems to be fixed. Hallelujah.

Thanks everyone for the helpful suggestions and ideas. I tested most everything that everyone here suggested. At some point I got test fatigue and I stopped making useful interpretations from the tests I was performing.

If the hose was rubbing check the braid closely if there is any damage to the braiding replace it. Braided lines are not very tough on abrasion and damage can cause a line to blow out.

Good idea. I will check it and report back here for completeness, and hopefully to help anyone who runs into a similar issue in the future.