Help! brake scraping noise

BriceJohnson · **Joined:** Thu Apr 13, 2006 7:33 am **Posts:** 2230

Anyone wanna help me diagnose this problem?

I recently did the brake pad replacement on my mazda3 to hawk hps pads (please lets not turn this into a "which brake pad is better" discussion though).

I had the front rotors turned rather than replacing them. Put everything back together, bedded the pads in, and all was good, stopping power was great, I liked the feel, everything was quiet. Now, about 3 weeks after, there is a scraping noise under light braking, but its not a constant scraping noise, its definitely like its scraping only for a small part of each rotation (period of the scrap is correlated to wheel speed).

I took everything back apart, cleaned the back of the pads off real well and reapplied anti-squeal to the back, roughed up the pads with some sandpaper, and bedded them back in again following the procedure on the box the pads came in (6-10 35-5 mph moderate braking; 4 45 5 mph hard braking, let cool without dragging brakes). The noise is still there exactly as it was before.

At this point, I'm trying to figure out what to do next to try and get rid of this. I'm inclined to replace the rotors, but want to make sure that it makes logical sense to do so. Here's my theory (which may be total bullshit):

The guy at carquest noted when he turned them that "they did have some pretty bad runout, but he was able to true them up ok". The wheel did have a pretty distinct shake under braking before I started all this (not to mention the rotors are the original rotors, w/ 95k miles on them). Is it possible that they have continued to warp a bit more causing a high spot and thus the periodic "scraping" with each rotation under light braking? I HAVE been stabbing the brakes pretty hard recently, testing out my new found stopping ability. Theres no shake in the wheel under braking, but could this just be the beginning of rotor warpage getting worse?

Worth noting, I DID verify that the pads aren't in backwards. . . (sorry Jeb, couldn't resist)

Aaron Buckley · **Posted:** Mon Dec 22, 2008 11:05 am

I assume these are Hawk blacks? If so, yes, replace the rotors. 95k on a set of front rotors is a butt load. If they were that warped prior, I have a tough time believing they had enough material left to safely turn them.

Personally, I never, ever, turn rotors. On all of the cars I've owned, the rotor prices range from $25 per rotor to $175 per rotor, yet I still think it's always best to just replace them.

In your situation, you had a warped rotor(s) that had material removed to true them. Now that lack of material has a tougher time getting rid of heat (less mass) and the bedding process alone produces a good amount of heat (especially with a more aggressive pad). The rotors then warped again. - AB

steve remchak · **Posted:** Mon Dec 22, 2008 11:11 am

you shoulda installed BHP's they are way better. :lol:

you started it.

anyway, Hawks are known for leaving "spotty" deposits on the rotor. that and brake squeal with a more aggressive pad is normal. and that would be my uninformed opinion.

of course what Aaron said is way better.

BriceJohnson · **Joined:** Thu Apr 13, 2006 7:33 am **Posts:** 2230

I believe they are the blacks, I dunno. They are black. Its the HPS "street" compound. The rears make no noise whatsoever.

I've basically learned my lesson on turning rotors, I had the rears turned as well, and they did such a terrible job (feed rate on their lathe was way too fast and ended up grooving them) I ended up having to replace them as well. I'm kinda pissed about it, but know if I go and piss and moan I'll probably not get my money back anyways and waste away my afternoon doing it. I just replaced rotors on my old integra b/c they were only $25/rotor, but the 3's rotors are more expensive ($45/ea for rear rotors, $65/ea for fronts) so turning them sounded like it made more sense.

Would a warped rotor cause the sort of periodic scraping noise I'm describing though? Thats what I want to be sure of before I shell out the dough for the new rotors. Thats my best guess, but I'm not sure. If it were the pads, I'd think it would be a constant scraping noise, not to mention would have been there all along as opposed to showing up 3 weeks later, but I dunno.

Wes Eargle · **Joined:** Mon Oct 27, 2003 9:47 am **Posts:** 3683

steve remchak wrote:

you shoulda installed BHP's they are way better. :lol:

That might be kinda hard to do since they're no longer in business.

Todd Breakey · **Posted:** Mon Dec 22, 2008 2:37 pm

BriceJohnson wrote:

Help! Brake scraping noise

Talk to Jeb. I hear he learned what not to do when completing a brake job recently. :poke:

Wes Eargle · **Joined:** Mon Oct 27, 2003 9:47 am **Posts:** 3683

Brake rotors don't actually "warp". A "warped rotor" feeling comes from a nonlinear deposition of brake pad material on the surface of the rotor.

Could you have parked the car too soon after you bedded the rotor in and didn't let the pad and rotor cool properly?

Aaron Buckley · **Posted:** Mon Dec 22, 2008 2:53 pm

Wes Eargle wrote:

Brake rotors don't actually "warp". A "warped rotor" feeling comes from a nonlinear deposition of brake pad material on the surface of the rotor.

I must be wrong, but I would think they could warp. Warping is caused by large differences in temperature across metal, or overheating a metal to the point it loses it shape.

I would think a brake rotor could see either. Otherwise, why does a cylinder head need to be checked for warping after it was overheated? It's not due to deposits left by the head gasket.

I may be completely wrong too, but I am curious. - AB

BriceJohnson · **Joined:** Thu Apr 13, 2006 7:33 am **Posts:** 2230

I've read that. I was very careful after break in, and didn't even TOUCH the brakes until I got back to my driveway (the bedding in instructions said very specifically don't drag the brakes), where I pulled it in, killed the engine, and left it in gear, so I doubt thats the issue

The other thing that leads me to believe that it wasn't pad deposition is that I installed the pads, bedded them in the first time, and drove it for 2 weeks of so with no noise. The noise then mysteriously appeared well after bedding in.

Before turning, there was significant runout (whether from pad deposits or actual warpage) in the rotor before it was turned. I know rotors don't USUALLY warp, but I think after 95k miles and 3 seasons of autocross, its believable to me that this rotor actually WAS warped and that that warpage has continued since i've been beating on these brakes recently "trying them out".

Then again, I could be full of it. . .

edit: This is what wes is talking about I believe:

http://www.stoptech.com/tech_info/wp_wa ... disk.shtml

Aaron Buckley · **Posted:** Mon Dec 22, 2008 3:05 pm

That's an good article. I learned something from this myth too:

MYTH # 6 - The brake fluid reservoir should be topped up during routine service.

In most modern passenger cars, the brake fluid reservoir is designed with a specific volume and is equipped with an internal float. The volume corresponds to the amount of fluid that will be displaced when the pads have worn to the point of replacement plus a generous reserve. When the replacement point is reached, the descending float completes an electrical circuit and a light appears on the dash warning the driver that the pads should be replaced.
If the brake fluid is topped up the first warning of warn out pads will be the screech of steel backing plate against iron disc. This will be both annoying and expensive.

- AB

George Bright · **Posted:** Mon Dec 22, 2008 5:42 pm

When the guy turned the rotors did he turn them so that the whole pad is riding on a new surface. I have had a set of pads that that contacted the rotor closer to the inside edge than the old pads and were runing on a couple of mm of rough rotor surface. Also if he did not turn them deep enough to clean all of the deposits off of the iron surface you could already be getting uneven areas of material exchange between pad and rotor. So the "warping"process begins anew.

One other thing I had happen to my old Datsun. There are springs that ride over pins through the pads. The spring pushes the pads apart. I had one get distorted and it rubbed aganst the edge of the rotor and gave a scraping sound.

If you cannot find something like that I would replace the rotors.

Sean O'Connell · **Posted:** Mon Dec 22, 2008 8:15 pm

did the rotors still have the machining spiral cut into them? the shop should have sanded them down so there were no directional grooves cut into the rotors, it can cause weird things if that happens. brake rotors can warp, in addition to pad deposits, and hot spots which all create a similar feeling and can be mistaken for a warped rotor.

personally i would have replaced the rotors to begin with, because thats a lot of miles and if they had "pretty bad runout" the thickness of the metal is probably nowhere near even and would cause uneven heating/cooling of the rotor and in turn could cause the rotors to warp again in a short period of time.

Pete Guthrie · **Posted:** Mon Dec 22, 2008 8:43 pm

are the pads on backwards, or do you maybe have rocks in the brakes possibly

BriceJohnson · **Joined:** Thu Apr 13, 2006 7:33 am **Posts:** 2230

Sean O'Connell wrote:

did the rotors still have the machining spiral cut into them? the shop should have sanded them down so there were no directional grooves cut into the rotors, it can cause weird things if that happens. brake rotors can warp, in addition to pad deposits, and hot spots which all create a similar feeling and can be mistaken for a warped rotor.

personally i would have replaced the rotors to begin with, because thats a lot of miles and if they had "pretty bad runout" the thickness of the metal is probably nowhere near even and would cause uneven heating/cooling of the rotor and in turn could cause the rotors to warp again in a short period of time.

Yeah, lesson learned, new rotors have been purchased, and we'll see Wednesday morning if that solves the problem. Unfortunately I don't have time to install them before then. I'll update this post to let everyone know if it solves it. Thanks to all of you for your helpful suggestions.

Actually, the BACK rotors had a bad spiral in them, and made a totally different noise (it made a big whirring noise when stopping). I already junked those and replaced them. The fronts were fine for a while, but I'm guessing that their age is the source of the problem. Thats what I get for trying to be cheap I guess.

Vincent Keene · **Posted:** Tue Dec 23, 2008 8:11 am

Aaron Buckley wrote:

That's an good article. I learned something from this myth too:

MYTH # 6 - The brake fluid reservoir should be topped up during routine service.

In most modern passenger cars, the brake fluid reservoir is designed with a specific volume and is equipped with an internal float. The volume corresponds to the amount of fluid that will be displaced when the pads have worn to the point of replacement plus a generous reserve. When the replacement point is reached, the descending float completes an electrical circuit and a light appears on the dash warning the driver that the pads should be replaced.
If the brake fluid is topped up the first warning of warn out pads will be the screech of steel backing plate against iron disc. This will be both annoying and expensive.

- AB

When you install new pads the caliper piston(s) will be pushed further into the bore, thus rasing the fluid level in the reservoir. Adding more fluid would make no sense.

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Help! brake scraping noise

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