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Knock, knock! What?!?

I own a 2005 manual Honda Civic LX with 53,000 miles and no prior garage history, except oil changes.



Previous “incidents”: About 2 1/2 years ago I dropped the front left wheel off the corner of a cattle guard but easily drove out with no apparent damage to car, just to the grass. A little over a year a go an inexperienced driver was learning clutch driving in my car, got confused with all the pedals while parking and drove over a small cement barrier. No apparent damage to car, I drove it off the barrier easily.



History of present illness:

Right front wheel bearing goes bad. Bearing replaced. Knocking sound with braking starts in same wheel about two weeks later. Brakes checked, serviced, “hot-spot” on brake pad ground down. Knocking returns about a week later. Brakes checked again. Another “hot-spot” ground down, piece of rust removed from God-knows-where, “take it and try it again” they say. Knocking returns within a day or two. Back to the shop, check the brakes, check the rotor, “take it and try it again”. Knocking persists.



Present symptoms:

Irregular knocking during last two seconds of braking period, only when moving forward and only after brakes have been used consistently for 1/2 hour or so, allowing them to heat up. Sometimes the knock sounds like it is coming from the right front, sometimes from the middle front of the car, sometimes loud, sometimes soft. Sometimes it knocks four times, sometimes once, twice, whatever. But it won’t do it in reverse and not when the car is “cold” and not even consistently when “hot”. They say the brakes are fine, the axel is fine, the alignment is fine. But they have heard the noise and know that I am not making this up! Someone please help me before something really expensive breaks!! My mechanic is not getting anywhere.

I barely even know how to address this post. All of this talk about grinding down hot spots and removing rust is beyond me and if nothing is lost in the translation between the shop and yourself then you’re being BSed.

Let me ask this first. Is your car equipped with alloy wheels or wheel covers?
If it has the latter, then remove the right front cover and go drive it down the street. If the noise is gone then the spring clips on the wheel cover are loose and the noise is caused by the wheel cover flexing on the wheel.

I saw the comments about “hot spots” and rust and I was thinking to myself,what can I say, I have never dealt with a “hot spot” in any sense much less one that has been identified as causing noise.

What I can add/suggest is, are we off target with blamining the brakes for this noise? Just as a idea, possible body “flexing” noise.

Kind of sounds like missing brake hardware. There could be missing O-rings or bushings.

Hot spotting of rotors does do indead occur. As matter of fact rotors don’t actually warp, but instead they end up with thickness variations when they get hot and aren’t allowed to cool down properly. And once these hard spots develope, no amount of machining/turning of the rotors is going to remove it. Because that hard spot is in the metal of the rotor itself.

New brake pads and rotors, and the proper break-in procedure for the brakes will most likely get rid of the knocking noise when that hard spot comes around on the rotor(s), and causes the brake pad(s) to be pushed into the caliper.

Tester

I agree that rotors can have hot spots but have to respectfully disagree that they cannot warp. I’ve measured and seen too many of them wobbling on the lathe.

One would think that if hot spots were the problem this shop should have solved this after repeated trips in.
As of yet, the OP has not really provided any info as to exactly what was done with the brakes other than mention hot spots, rust, etc. and one would think that if hot spots, parallelism, etc was a problem the OP might have mentioned a pulsing brake pedal or shudder?

http://www.babcox.com/editorial/ic/ic60838.htm

Nowhere in the artical is the word “Warp” used.

Tester

I’ll add this much: there is no shuddering, vibrations, etc to be felt. Not in the pedals, not in the steering wheel, not even through the seats. I’m not convinced that the brakes are the problem since it doesn’t happen EVERY braking instance and only during the last few seconds of continual braking. Although, it is ONLY associated with braking. When I let the car slow down and stop by itself, there is no knocking. I can try removing the wheel cover, but this is a little too loud for something that small. And that shouldn’t change with the heat factor. My curiosities are: 1)could a primary problem have caused both the wheel bearing to go out and now the brakes/rotors to be warped? or 2)could the bad bearing have caused the brakes/rotors to be warped?

First off, I’m not saying that the wheel cover is even the problem; only that it COULD be. And it’s a simple matter to weed that out.
Don’t be surprised about this. I’ve run into it several dozen times and some of them can pop pretty good and are erratic about doing it. I discovered this on several vehicles after the owners had flushed good money down the drain replacing halfshafts and brakes.

As to the tech writer linked to I don’t put much faith into those guys. According o his bio he’s 44 years old, has been a tech writer for 25 years, and apparently never worked as a mechanic in his life or had any brake lathe experience.
And cast iron does warp. Not only have I seen it countless times on brake rotors there is also a reason why an automotive machine shop has a surface grinder (to plane cylinder heads) but also equipment to deck blocks and line bore main bearing saddles. Warpage is the cause of all of those problems.
Wished I had a buck for every Subaru cast iron throttle body I’ve had to file flat again. Heat warpage, sucking air, leaking gas internally, and nothing but headaches.

A very good friend of mine who lives a couple of blocks away (70+ years old, retired machinist) is without a doubt the most technically astute guy I’ve ever known. I trade him car advice and in return he trades me metal lathe/mill and metallurgy advice.
This guy has worked machining engine blocks and heads from bare castings along with putting in a number of years as a custom gunsmith (10-20k dollar shotguns/rifles) and he has told me that brand new engine block castings warp.
Since the foundry was on-site the blocks were cast, tossed out in the field, and allowed to ripen like tomatoes on the vine for several years before they were even machined.

It seems to me that if there is a rotor problem you should be feeling something in the steering wheel or brake pedal.
Go to a deserted road and run the car up to speed. Bring it slowly to a stop with the park brake only and note if the noise still exists.

The bearing will not have anything to do with a warped rotor, hot spots, or parallelism, etc. but an improperly installed bearing could possibly cause a problem. Anything loose in the suspension or wheel bearing can mimic a warped rotor and should be felt in the steering wheel or pedal. Hope some of that helps.

So I was talking to a friend last night who has an '01 Civic and he said, “I had the SAME problem! First the wheel bearing went out, followed by the knocking with braking issue!” Except it took EIGHT trips to the mechanic before they figured out what the problem was. I’m only halfway to that number. But his issue was a bent hub. So back to the shop we go on Tuesday to have the hub measured (and the rotor) to see if its bent.

Again on a BMW (a very old coupe,I was young also) customer complaint was brake pedal pulsation some noise,repeated rotor replacement,did not fix, the outer bearing race for the inner bearing was loose in the hub,would fall right out,never saw the same problem again.

I respectfully disagree that rotors do not warp. They warp. OK4450 posted some indisputable photos from his lathe a while back. I personally have felt severe warpage while spinning the wheels by hand and letting my fingers ride lightly over the surfaces. And while my hand doesn’t have a built in lateral runout gage, it didn’t take one in this case. The warpage was definite.

Having said that, I think the OP should try another shop. This should not be “rocket science” to repair.