jleonard71

About a month ago I replaced my worn-out OEM front pads with a set of Carbotech Bobcat pads. When I changed the pads I measured the rotors at about 29mm, and there weren't any grooves or spiderweb cracking around the holes, so they aren't to the point of needing to be replaced yet. They were replaced before I owned the car (at 30K per the dealership service records), and I have 49K on the car now so they only have 18K on them, so I decided not to replace them.

Everything was perfect at first - the stopping power was great, no fade at high speeds, less dust, and absolutely no squeaking or other noises. Well then the past few days they have started squeaking a little bit at very low speeds, so I tried bedding them in again and the squeaking went away. But then this morning on my way to work I noticed a nasty grinding sound when coming to a complete stop. They sound fine at high speeds, but when I'm going very slow (2-3mph) and brake to a complete stop it makes a horrendous metal-on-metal grinding noise. The grinding is so bad that I can even feel it in the pedal. What the heck could this be? I did a quick visual check and everything looks good, but I won't be able to take the wheels off and get a look at them until tonight after work. I'm just concerned that the car might be unsafe to drive because of how bad the grinding is. It sounds like it does when a pad is worn all the way down to the backing plate, but these are brand new pads so that's obviously not it.

Any thoughts? And sorry for the long post, just wanted to give some background info.

DHRP

iTrader: (2)

Did you get these from Jeff? I would call Carbotech. I believe there was an issue with a batch that had too much material on it and they had to be recut.

jleonard71

Yes, I sure did! And these are actually a replacement set which was already sent back and swapped out for the new design. They were working fine for the first few weeks, I just started having issues the past few days.

lobuxracer

iTrader: (2)

My Bobcats are a little noisy at 1 - 2 mph and they sound like they're grinding. They're not. It's just the nature of the compound with Brembo rotors.

jleonard71

One thing I was just reading in another thread is that with some aftermarket pads you don't need to reuse the stock shims. I did put the stock shims on the new pads, and I coated the inside of the shim (where it touched the pad) with anti-squeal compound as well as the circles on the back where the pistons make contact with the shim. Is that the right way to do it for the Carbotech pads?

jleonard71

But this just started this morning, these pads have been on for 3 weeks and they have never made this noise before. And it is so loud that I can hear it over the radio, and I can also feel the vibrations from the grinding in the pedal.

I just went out at lunch and drove around a little again, and this is definitely a nasty metal-on-metal grinding noise rather than typical brake squeal. Could something have possibly gotten lodged in between the pad and the rotor?

lobuxracer

iTrader: (2)

It's possible. The pads are silly easy to check, even without removing the wheel. As long as you clearly have pad material between the backing plate and the rotor, it's not directly a pad issue.

jleonard71

I guess I'll just have to check them when I get home, I was just hoping I could get some ideas on what the problem might be.

One thing I did notice with the rotors is that, even though they are within specs at 29mm, they do have a pretty deep "lip" grooved along the outer & inner edges. But again, it's been that way since I first installed the pads so I don't see why that would cause an issue now when it wasn't before.

CaptAwsm

Sometimes you can get pebbles stuck between the pad and rotor, used to happen to me when offroading.. not sure how/if it could happen on the F tho.

What I would do is a hard quick brake, a couple times. Like while moving, slam on the brake and let off immediately after; then repeat a couple times. It would force the pebble out usually.

lobuxracer

iTrader: (2)

There's nothing significant about the lip on the edge. I've heard people try to blame the lip for all kinds of silly things, but it does nothing good or bad.

jleonard71

Also, I noticed that it seems to be only on the driver's side. Here are some pics (driver's side on top, passenger on bottom).

jleonard71

That's possible. I do live in AZ and there is always a lot of crap on the freeways, plus I drove through a stretch of road this morning that was gravel due to construction. I'll try a few hard stops and see if that helps at all.

tenspeed

iTrader: (1)

Another possibility is that the pad has a hard spot in it. It would be hard for a stone to fit in the tight space when the brakes are not on.

lobuxracer

iTrader: (2)

By the same token, a nearby shop had a car towed there because the brakes were making a horrible noise, and a rock fell out of the caliper as the car was backed off the flatbed. Problem solved. Strange for sure, but it happens.

jleonard71

Well last night after work I did about 30 minutes of spirited freeway driving with speeds up to about 110mph and then hard braking back down to 60mph, and now the sound is completely gone. Don't know if it was a pebble that got lodged in there or a hard spot on the pads or what, but it sure was weird. I've never heard brakes make that sound before unless they were completely worn down to the backing plate.

BTW, was anyone on here driving the F that was cruising with me on the freeway in the Tempe/Chandler area? I pulled onto the 101 right in front of you, and then you stuck with me until I got off the 202 at McQueen. Too bad I had to get off there, because I had just pulled up alongside a Shelby GT500. That would have been fun - two F's vs. a GT500!