Miata grinding noise on braking
 

The car has developed a sound just like the one you'd if the disks got pretty rusty and you then apply the brakes. Except that this noise does not go away. No sounds at all during coasting, even at low speeds. It only happens with the brakes on. It does not seem to impact braking performance at all either. Also, at times, after driving, it seems to improve, but then it returns.

IIRC, previous owner installed some AutoX-friendly, performance Hawk pads.

I put the car on the lift and pulled the wheels. Visual inspections shows plenty of pad life, and good looking disks. The rears have some uneven radial streaking, but nothing I could attribute the noise to. Unfortunately, the NC has crazy-expansive inner shields, providing a VERY limited view of the inside disc surfaces - particularly in the rear. I could not see rocks or anything like that stick between the discs and shields either.

I figure I can:

1) Remove the pads and better inspect inner disc surfaces and pads.
2) Even if 1) reveals nothing major I could just change the pads (and?) discs.
3) Let it go. This worries me because given the amount of life left and use fo the car, this could be a LONG while.

Any thoughts?

Pop the calipers and check. I usually see greater wear on the piston side, so that's worth checking.

If it's good, reassemble and don't worry about it.

Not saying this is what your problem is, but I once had something similar when a pad had actually come separated from its backing plate. First glance everything looked fine with plenty of disc life left. When I then pulled the caliper. . . . oops there it is, as the pad fell off

Yeah, I have a feeling I have no choice but to pull the pads and check them.

It’s less effort to pull a caliper than popping the wheels off. I hope it’s still on the lift. :)

I pulled the wheels to check it a week ago and have been driving it since. Either way it’s going back up.

Well, I think I found the problem. I took photos.

First, a photo of the rear right disk from the outside. Weirdly it shows some pitting which I've never seen before. I then took off the pads. Note the MASSIVE scoring on the inside pad. WTF? did a rock get stuck inside?! I held the pad against the inside of the disk and you can see that past the scoring, the disk wasn't even making contact with the pad and a decent section is untouched and rusted.

Then to the rear left. Disk looked a LOT better with hardly any of that scoring showing. Pads look a lot better as well, but again, there is a weird groove on the inside pad. A photo of the disk from the inside shows it looking awfully rusty considering it seems to have very little wear.

In both cases calipers look good and glide easily.

Oh, and the front brakes are excellent. For reference I took a picture of the outside and inside of the front right corner.

Finally a photo confirming the previous owner installed Hawk pads.

Well, i’d obviously replace the rear pads and rotors. Did you confirm that the pins move as well?

It took me a long time, but I've learned that if a bicycle, a motorcycle or a car make a funny noise. It's not to be ignored...

No doubt. I'm buying new disks and pads. Any harm in going with OEM pads in the rear with Hawk ads up front?

Pins glided smoothly on both calipers.

matching is better. otherwise, you can throw bias off.

I figured. I'm buying new pads all around and new rear rotors.

Update/rant:

I went ahead and ordered a full set of OEM pads and rear rotors - or so I thought.

Waited 1.5 weeks for parts to arrive only to find I had received front rotors. Yup, I ordered front ones by accident. In my defense, the site had suggested these when I added the rear pads and the image looked (and still does) like solid discs, not vented like the fronts are. In addition, despite ordering the the proper kit, I got rear pads with no clips.

They were good enough to issue me a return label for the front rotors (I picked up shipping on the rears - not cheap) and they sent me a new set of pads. Except I received front pads. :rolleyes: Forget it. I'll just keep them and clean and reuse my rear pad clips.

Fast forward a couple more weeks and the rear rotors finally arrive. I go to put them on on Tuesday night and (long story) I cross-thread a bolt into a slide pin.:mad: Ugh.

Yesterday morning I call the dealership and order all 4 rear caliper bolts (the gunked threads are partly to blame for the cross-threading) and new rear, lower, slide pin. They came in this morning. I go to pick them up and guy had ordered the front ones. HOW?! I read him the freakin' part numbers over the phone. GRRR.

So hopefully tomorrow I'll get the proper parts and get the stupid car down from the lift after nearly a month.

I had to look up cross thread only because if I read the definition correctly it means you stripped it ...

If so I have done the same thing many times ... so frustrating :mad2:

Well, I know in common parlance people use "stripping threads" and "cross-threading" interchangeably, but as a machine design engineer, stripping threads means that you overloaded too few (or soft/weak) threads and the threads were sheared off under axial load. Cross threading means the threads did not follow their intended path and as a result the peaks of the threads were flattened creating a crappy new thread path.

It was so annoying. I was having trouble getting the screw in smoothly. I pulled the pin and tried the screw in my hands and it as tough to get it to fit in, so I figured the resistance was natural. But the e-brake cable ads an annoying side load. I thought I had it, but obviously did not. I'm hoping new screws will fix this. Unlike other cars, where screws are very cheap, these are meant to be reused. They are $8 a pop. For Mazda screws. :rolleyes:

cross threaded is still tight! :lol:

Yes indeed.

Got it ... thanks for explaining the difference .... I’m sure you’ll get it done !!! It does get frustrating when things don’t go as they should but when you get it done the satisfaction will be there :thumbup::thumbup:

As frustrating as this is, at least the Miata is not you only ride. Imagine if your were 18 years old right now and this just happened . . . .you just spent the only money you have, and your ride still sits on a block or two (cause no way you can afford a lift)

True. Although admittedly, had that been the case, I would:

1) Not have removed the rear rotors and rendered the car inoperable until I had the correct parts, or
2) Gone to a local dealer or a car parts store and gotten brakes that same day.

The thread issue costing me 2-3 days? Yeah, I would have been hosed with that. And yes, the car would be in blocks on a crappy driveway (in the rain, given the weather the last two days).:ack:

My first brake job was on my 190E 2.6 right out of school and I was overly ambitious and decided to do a full brake job and replace the flex lines as well on a Sunday. I took too long (was missing tools and had to bike to stores to get them) and created a massive air pocket in the system. I had to borrow my dad's car to go to work the next day and car sat on stands for a day. So I know exactly what you mean.

Are the threads something you could fix by chasers/thread fixing tools? Or are those parts easy/cheap enough to replace themselves?

They are not a particularly common thread. It's fairly fine. My set doesn't have that pitch.

I also just heard I won't get the new parts until mid-late next week.:rolleyes:

Finally got all the parts and finished the job. Brakes are great. OEM pads seem to have slightly less sharp feel than the Hawks, but for the street are fine.

Now on to the coolant flush and a new expansion tank, thermostat, and accessory belt. All items preventive except for coolant, which I have a feeling is the factory stuff and the car is almost 10 years and 95k miles.:ack: