Brake Rotor Question

I have developed a decent harmonic road vibration that I have really started to notice lately. It does only occurs when the car is moving, and it is directly proportional to the speed of the car. Is this a common result of worn rotors. I have tried to eliminate the problem by rotating my tires. I moved all the fronts to the back, and vice versa. I have also reduced my tire pressure from 40 psi to 30 psi, and nothing made a difference whatsoever.

I am assuming these are the original rotors on the car with nearly 140k miles. I wll change the rotors when I do the brakes again (getting close on the front set). The problem I have gets really noticable when I slow down, but it doesn't really seem to change with the brakes on or off, but it does increase as I slow down. That's the point when the engine goes quiet, and I just hear the road noise. When I hit 70 mph, it seems to be a constant humming vibration, and by then, it's hard to notice the harmonic nature.

Any thoughts on this? I'm guessing it's the rotors.

get any codes? perhaps an abs wheel sensor?

No codes from the Vag-Com. Is that a common symptom of an ABS wheel sensor?

It does not occur when the car is moving, and it is directly proportional to the speed of the car.

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Did you mean it only occurs when the car is moving? If the vibration occurs only when applying the brakes it is most likely rotors. If it only occurs at certain speed with the brakes not applied then it is most likely wheel balance.

Matthew_S said:

Did you mean it only occurs when the car is moving? If the vibration occurs only when applying the brakes it is most likely rotors. If it only occurs at certain speed with the brakes not applied then it is most likely wheel balance.

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Yes, that is what I meant to type. It definitely occurs without the brakes applied. I'm not certain if it changes much with the brakes applied, either. I thought about it being a wheel balance issue, but it didn't seem like I changed the problem at all by moving the front tires to the back, and the rears up front. Then again, it may feel like the exact same problem either way.

I have also been pondering if it is a wheel bearing or hub problem. I have never had one of those, so I'm not sure what to look for. I think my next move needs to be to check the balance on my wheels.

BTW, what does a wheel balance problem feel like at low speeds. At around 20 mph, it seems to be moving at a frequency of around 120 cycles per minute...just from guessing.

I may actually try to time it and see if it corresponds to each rotation of tire. At 120 cycles/minute, it seems like it should correspond to around 10 mph, but that is surely speculating at this point.

Is that what a wheel balance problem would do?

Newgene said:

(snip) It definitely occurs without the brakes applied. I'm not certain if it changes much with the brakes applied, either. (snip)

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__. This certainly doesn't sound like a rotor. Usually any rotor problem (worn, warped/"potato chipped", rough surface, etc.) will cause most problems when the brakes are applied. I can't help much with where to look but I'd definitely look elsewhere than the rotor.

A wheel balance problem usually won't be noticeable at speeds as low as 20 MPH but it could be a bad tire. If there was no difference at all after rotating the tires then it is likely not a wheel balance or bad tire issue. Does the vibration cause the steering wheel to shake or does the whole car shake? What ever the problem turns out to be the rotors are the one of the last things I would suspect.

It only causes a steering wheel shake at higher speeds (65+ mph). It is a shake to the whole car because my wife feels it just as much while riding down the road. The vibration is there at all speeds, and it is a function of vehicle speed.

I seem to have noticed it after I changed the timing belt, but I also rotated the tires at the exact same time. Yes, I did jack up the engine, so I thought about the motor mounts. However, I get absolutely no vibrations when stopped...at any engine rpm. And, the sound is definitely a function of vehicle speed rather than engine speed.

I am just wondering if when I rotated the tires, I just moved the problem to a different wheel, and it somehow yields the same results. Another item to note is that one of my tires seems to be cupped a little, but I'm probably due for a new set anyway. I just hate to start chaning tires, rotors, brakes, etc. without knowing what is going on.

Could this be some kind of wheel bearing issue? Do they usually make noises/vibrations like this?

A little more clarity. It's not really like an instantaneous shake. It's more like the car is hitting a very mild road grating that they use to tell people they are getting close to a stop. Again, it is very mild, but if it were heavier, that would be similar. It also feels like a harmonic vibration you would get from a bad rotor or brake pad, but it does occur while you are not braking.

I'm just kinda a loss on how to begin troubleshooting this.

Look at your wheels, do any of them not have wheel weights on the outside edge of the rim?

david_594 said:

Look at your wheels, do any of them not have wheel weights on the outside edge of the rim?

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I looked at them yesterday as I rotated the tires, to see if I had any locations that looked like one fell off. I really didn't see anything, but I noticed I had weights on the inside of the wheels. I wasn't really looking extremely close, but I could always run the car to a tire shop and them all checked for balance anyway. I'm sure the cost would be close to having them actually balance them, but if that would be my next logical step, I'd surely do it.

One of my Aristos had the exact same problem when I got them last year. Vibration only showed up at 65+ mph (Not that one would drive over 65, of course..) and actually got a little better when I was on the brakes.

Problem ended up being a very slightly bent front passenger side wheel. Local garage was able to balance it out with wheel weights and I've since moved it to a rear wheel. Voila - no more vibration in the steering. If it's coming through the steering wheel, it's probably a front wheel causing the issue.

Bring it to a garage and attempt to have them rebalanced. If it's just missing a weight, you're done. If it's bent, they'll find out when they put it on the balancer.

BlueCTTDi said:

One of my Aristos had the exact same problem when I got them last year. Vibration only showed up at 65+ mph (Not that one would drive over 65, of course..) and actually got a little better when I was on the brakes.

Problem ended up being a very slightly bent front passenger side wheel. Local garage was able to balance it out with wheel weights and I've since moved it to a rear wheel. Voila - no more vibration in the steering. If it's coming through the steering wheel, it's probably a front wheel causing the issue.

Bring it to a garage and attempt to have them rebalanced. If it's just missing a weight, you're done. If it's bent, they'll find out when they put it on the balancer.

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Actually, my problem seems to be really noticable at the lower speeds. The steering wheel shake only seems to come in at higher speeds, though. The smoother the road, the more pronounced the vibrations are and I really noticed the on/off nature of the vibrations. You can feel the vibrations through the floor of the car.

Again, I do have one tire that appears noticably cupped. BTW, would a cupping sound be similar to what I am describing?

I'm planning to drop the car off at a tire shop to check the tires, balancing, wheels, etc.

ahh, missed that detail when i read through everything (my bad..) you'd hear it more if it were flat-spotted, but that would be more of a thumping noise. If it was just uneven wear, I'd think the noise would just be constant and not harmonic, assuming the uneven wear was consistent through the entire circumference of the tire. Further, if it were only one tire, you wouldn't feel it through the steering as much once you moved it to the rear axle.

You mentioned a humming sound - maybe someone else could chime in here... but is it possible a wheel bearing or something else in a hub is going bad (especially after 140k)? The rotor would have to be about ready to fall off if it were warped bad enough for this to suddenly happen. As everyone else mentioned, I'd be surprised if that were causing the problem.

Can you get the car up on jackstands and manually rotate the wheels? Might help to isolate the offending wheel if you could hear something funky going on (if you can get something to make noise)..

Also, that cupping might be a sign of a bigger issue depending on how bad it is.. check the suspension on that wheel. At 140k, if it's all still stock, chances are the struts and shocks might be on their way out (I'm surprised they made it this long ).

(Please feel free to call me out if it sounds like I'm talking out of my a$$, I'm sure it's bound to happen at some point...)

Maybe check the engine mount bolts. it's a long shot but I have talked to at least one person who had a strange vibration for a couple of weeks before the engine fell out.

Matthew_S said:

Maybe check the engine mount bolts. it's a long shot but I have talked to at least one person who had a strange vibration for a couple of weeks before the engine fell out.

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Ouch!

Matthew_S said:

Maybe check the engine mount bolts. it's a long shot but I have talked to at least one person who had a strange vibration for a couple of weeks before the engine fell out.

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Yeah, I can imagine that was a pleasant surprise

Well, my wife just took the car in to the tire shop. Immediately, they found a problem with my passenger side front strut. I'm not looking at the vehicle, but I believe I know what they are talking about. There is a gap under the hood beneath the cap on top of the strut. They showed my wife that there is play when you pry on it with a tire iron. They did not ride in the car, and my wife did not really say anything about the harmonic nature of the noise/vibration.

So, here is my question. Does a strut seem like it could cause the type of noise I'm describing. Yes, I believe that I have a problem with the strut and need to change it. However, could they have just found another problem that is totally unrelated to what I'm noticing? Does it make sense that a strut would cause that?

** Edit: I just spoke to Precision Tuning in regards to this, and they confirmed that a missing bushing at the top of the strut is common, but will not cause this type of sound. He thought maybe a wheel bearing, but if it is not making a significant noise, and it's just a vibration, it's probably tires, balancing, or possibly an alignment.

The car is now on its way back to the tire shop, and I'm going to try to be available by phone if they need me. I want the shop to take a look at the cupped tire, and even if they can put a used tire on the car and balance all the wheels, that would tell me more info about what is or isn't causing my problem.

Well, here is the update. The problem is solved, according to my wife. She just picked it up from the tire shop and she said it is driving smooth with no vibrations. After she brought it back, I asked the owner (local guy who I know) to throw two used tires on and balance the other two.

Man, what a relief!

wow - nice to see that was all it was. good stuff! I guess i'd still keep an eye out to see if the uneven wear comes back eventually..

BlueCTTDi said:

wow - nice to see that was all it was. good stuff! I guess i'd still keep an eye out to see if the uneven wear comes back eventually..

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I had one tire cup out pretty bad, and although they changed 2 tires and balanced them all, I'm hoping that one tire was the culprit. If so, I can also hope for it being just an isolated failure in the tire manufacturing...I think I'm hoping for a lot. I'll keep a close eye on it. I have a lift in the garage, so I'll be rotating more frequently than usual.

Thanks for everyone's advice.

Have you had your allignment check out recently?

david_594 said:

Have you had your allignment check out recently?

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No, but I plan to buy a set of Michelin Energy S8's from tirerack shortly. I just put the used tires on the front end, and my rears are getting close as well. So, I'll definitely have to have it checked before I put the new set on. I'll keep an eye on these to see if I see any uneven wear. However, if I get time to have the alignment done between now and then, I'll just go ahead and do it.

There is the firestone lifetime alignment deal. I think it cost something like $110 when I got it last year. Pays for itself fairly fast. Just something to consider.

You probably should take this opportunity to replace all the front suspension bushings.

yeah, at 140k on the stock suspension it's a pretty safe bet the entire front end needs at least a once-over look, if nothing more than for peace of mind...