Brake noise: what might this indicate?

[brad_d]

The car in question: 2000 Honda Civic, 27,000 miles.

The front brakes on this car has managed to wear down to the indicators, so we had a front brake job done at the local Honda dealer (OK, we can discuss the relative merits of that decision in another thread.). Fairly straightforward: they removed the rotors and resurfaced them, and installed new pads.

After the brake job, we heard noises that had not been there before:

• The noise is a pulsating rubbing/grinding sound that all observers agree seems to be coming from the right front wheel.
• The frequency of the pulsation is clearly in proportion to vehicle speed.
• The noise only occurs when the brakes are being applied, and stops immediately when they are released.
• I've never heard it at speeds above about 35 mph. When slowing down from a faster speed, that's the speed at which it starts.
• It's not always present, but it usually is.
• There is no perceptible pulsation felt through the brake pedal, or in the car's motion - just the noise.

We took the vehicle back and left it for them to examine (overnight service). The word they gave us was that they "spray-lubed the CV joint boot." No charge. The guy at the counter couldn't even tell me if it was the inner or outer boot, and the dudes who actually did the work had gone home. This, frankly, didn't make a lot of sense to me, but the noise did seem to be gone.

For about a day.

Knowing enough about this sort of thing to be dangerous, I jacked up the front of the car and popped both wheels off to see what I could find, if anything. I couldn't see any signs of strange rubbing or wear on the disc, or anywhere in the whole assembly. I pulled the pads out and looked at them: they seemed fine. Nothing looked obviously wrong.

Except: disc runout seemed, to my untrained eye, excessive. I don't have a dial indicator, so I can't measure it. However, the (floating) caliper travels quite a bit laterally on each rotation of the disc. I observed this by starting the engine and letting it idle in Drive (with both front wheels off the ground). Actually, this is the case on both sides, but the right (noisy) side is worse. If I use the machined outer surface of the disc as a mirror while it spins, the image moves perceptibly as the disc rotates: clearly, the surface of the disc is not precisely perpendicular to the axis of rotation.

The only basis I have for comparison is my own truck, which also has floating calipers. There is no perceptible wobble in the caliper as I spin the disc. The "mirror check" also reveals no perceptible motion in the image.

I want to be able to speak intelligently with the dealer when I take it back there. Does the noise I describe sound like something that might be caused by a excessive runout in the disc? Does the amount of runout I vaguely describe sound excessive in the first place? Am I barking up the wrong tree?

Any suggestions from the gearheads would be much appreciated.

[Gary T]

Does the noise I describe sound like something that might be caused by a excessive runout in the disc?
Yes.
Does the amount of runout I vaguely describe sound excessive in the first place?
Yes
Am I barking up the wrong tree?
I don't think so. I think you're spot on.

My guess is that the rotors were misaligned on the brake lathe, the result being that the plane of the braking surface is a few degrees off from the plane of the hub mounting surface. The analogy for warped rotors is a warped phonograph record (shallow "potato chip" curvature), the analogy for this would be placing an aspirin tablet under the record close to one edge--the record would be tilted relative to the turntable. Another possible cause, in fact, would be some dirt or debris having gotten between the rotor and the hub. It's also conceivable that the hub was warped from overtightening the wheels, but I'd hope that every Honda dealer in the country has known about this possibility for years and taken steps to prevent it.

Lubing the CV boot sounds ridiculous to me. In nearly 30 years of auto repair, I've never heard a noise from a CV boot. CV joint, yes (though quite a different type of noise), but not the boot.

From my vantage point, your common sense description of the calipers moving back and forth makes it clear that there is a problem with the rotors. I would think they'd have to acknowledge this and take responsibility for it. If, as I suspect, the rotors were set up crooked on the lathe (or if they're warped), they would have to be turned again--if they're thick enough to do so. They probably are, given that this is the car's first brake job and the rotors weren't scored. But if they aren't, the only good solution is to replace them.

[LolaBaby]

Did they take it apart the second time you took it in? Maybe a anti-rattle clip could be slightly bent and occasionally scraping the outer edge of the disc?

If the runout was that bad, I would think you'd have some mean pedal pulsation.

If you removed the pads, then replaced them, then did that eyeball-runout check, the caliper may have had some perceptible runout if you did not apply the brakes to set the piston back out.
Hmmm. Hard to say. Wait for GaryT.

[LolaBaby]

Hahaha! You beat me to it. Anyway listen to him.

[Gary T]

LolaBaby brings up a good point--you need to have things in normal position to evaluate runout. In particular, all four lug nuts should be equally tightened. This could be with the wheel on or off. If you checked with the wheels and lug nuts off, the rotor could have been aligned differently from how it is when you're actually driving.

[Gary T]

LolaBaby brings up a good point--you need to have things in normal position to evaluate runout. In particular, all four lug nuts should be equally tightened. This could be with the wheel on or off. If you checked with the wheels and lug nuts off, the rotor could have been aligned differently from how it is when you're actually driving.

[Northern Piper]

This is weird - exactly the same thing happened to me today, with the same noise following service of my Acura.

I'll take it in on Monday, and thanks to GaryT I'll at least sound like I know what I'm talking about, which is half the battle!

[LolaBaby]

Another thing...that I wanted to bring up, but it took forevers to get to the page and I had to go out...was... as GaryT said, most Honda dealerships should definitely use a torque wrench when tightening the lugs, and I'm not too sure about the newer models, but I recall that certain Honda years would have a better cut on the rotors if they were resurfaced on the vehicle.

[galen]

Everytime I have my brakes done, they want to turn the rotors whether they need to be turned or not. I examine the rotors myself, and if they look ok, I just have them change the pads. I have had no problem with this approach.

My experience has been that when rotors are removed, turned, and remounted, there is a damn good chance that there will be more runout than before they were messed with (usually none).

Did these rotors really have to be turned?

[Gary T]

Originally posted by galen
Everytime I have my brakes done, they want to turn the rotors whether they need to be turned or not. I examine the rotors myself, and if they look ok, I just have them change the pads. I have had no problem with this approach.

My experience has been that when rotors are removed, turned, and remounted, there is a damn good chance that there will be more runout than before they were messed with (usually none).

Did these rotors really have to be turned?

For the benefit of those who aren't familiar with the details: Resurfacing (= machining = turning) rotors involves grinding away the surface to get them perfectly flat and with the optimal surface texture. It's usually done with the rotor removed from the car on a piece of equipment called a brake lathe, though some shops have equipment to do the job with the rotor still installed on the car.

There's not universal agreement on the subject of resurfacing rotors. All rotors have specifications on a minimum "machine to" thickness and a "discard" thickness" (in some cases these are the same). It's almost always considered necessary and appropriate to turn them if they're scored or warped, assuming there's enough thickness left to stay within specs.

Disc brakes have an inherent tendency to make "annoyance noises," usually a high-pitched squeal (which can sometimes sound just like the pads' wear indicators). In normal use over the lifetime of a set of brake pads, the surface of the rotors will become glazed. Experience has shown that resufacing the rotors properly, which leaves a non-directional dull satin sort of surface, is often required to minimize the chance of noise. (Other steps, such as cleaning and lubricating--with the right sort of high-temperature grease--the points where the pads engage in their brackets, are also helpful in this regard.) So most shops, who need to guarantee their work and don't want customers coming back with noise complaints, are in the habit of routinely resurfacing (or if necessary replacing) rotors when they replace pads.

Now, the major brake pad manufacturers recommend resurfacing for optimal break-in of pads. But some (not all) car manufacturers recommend resurfacing only in cases of scoring or warpage. In certain cases, usually involving heavy vehicles, towing, and/or mountain driving, rotors that have been machined to the minimum limit will tend to warp because they can't effectively dissipate the heat generated by braking. And there are many different choices of pads available, some of which are specifically designed to not be noisy.

So what this all means is there is no hard and fast rule about resurfacing. Different people will have different opinions, often reflecting how they prioritize the issues of noise, durability, economy, etc.

If the rotors are turned, it is important that it be done with equipment that's in good shape and by someone knowledgeable and conscientious about using the equipment properly. Otherwise, as noted, it can make things worse.

[Mangetout]

In my experience, there are two things that mechanics mention when they want to rip you off (assuming that, like me, you are not an expert mechanic):
"Your CV boots were holed and leaking"
"Your Steering rack gaiters(sp) were worn/split"

Oh, hang on, it's actually three things:
"that'll be 300 quid mate"

[brad_d]

Thanks very much for the advice/info, folks!

One thing that I did not think about was the lug nuts - I did all of my own inspecting with them off. If I have a chance I'll take another look at them today with the nuts tightened down (I have a torque wrench, so I can get them right to the 80 ft-lb that the manual specifies).

When I took it back the first time, I don't think they even took the wheel off - they just lubed the boot and hoped I'd go away. Reason I say this is that there was a shim behind the outer brake pad which was kind of off-kilter - it was really obvious when I removed the wheel. I figured that this might be the problem, so I re-set it, getting the aligning "fingers" all back over the edge of the pad.

The noise didn't go away, and when I checked it again the shim was still properly aligned, so I dismissed that as a possible cause. Still, I think if they'd even pulled the damn wheel off when they "inspected" it they'd have noticed that.

In thinking about this, I'm lead to suspect that pedal pulsation would only be felt if parallelism of the two sides of the brake disc were bad - the piston(s) would be getting forced back into the caliper when it hit the "wide part" on each revolution. Runout simply drags the caliper back and forth on its pins - I'm guessing that if I pulled the caliper off completely (rather then just swinging it up) there might be wear on the guide pins from this?

I'll follow with updates/questions as the situation merits. Thanks much!

[Northern Piper]

Got my Acura back from the shop today. They said that a flange was in contact with the rotor and that was causing the noise. (Now that I look more closely at the OP I see that the problem there was when the brakes were applied; my noise was constant, just changing in pitch as I slowed down or sped up.)

Any rate, noise is gone, no charge for the follow-up, plus a free wash, plus they delivered the car to me at work - so I'm