# Humming sound - caliper or wheel bearings?



## nduetime (Mar 22, 2003)

I tried to post this in the MK2 forum but haven't had any responses so I'm here.
I have a humming sound coming from what I think is either my brakes or wheel bearings. I thought it was maybe stuck calipers but after research I think it might be wheel bearings and am looking for advise. 
I don't really notice it much if at all when driving. However, I hear squeeks when I brake which I'm sure has to do wil pads or brake dust. There are some times when I hear the humming when braking bust most of the time I always hear it when I go to accelarate after a stop. As the tire and rotor spin when taking off I hear the humming for a brief second then it goes away. This is why I thought it was a stuck caliper. I can't make out which side it's coming from but think it's coming from the back. 
I replaced the rear rotors, bearings and pads about 2 years ago. 
Any thoughts. Thanks-b.


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## 427+SS_iraceporsches (Aug 27, 2003)

*Re: Humming sound - caliper or wheel bearings? (nduetime)*

If you think you have a caliper sticking, then jack the car up on four jackstands, remove all of the wheels, and manually turn the spindles. If the caliper is sticking, you should be able to notice or feel it. 
If the brakes are squeaking when you brake, that may be slight rust, but not necessarily worn down pads; afterall brakes squeal to indicate wear while in motion, and will cease when you apply the brake, because the pads move in (farther than the squeaker) to contact the rotors to stop the car. Since the squeaker is designed to rub the metal and make noise (indicative of it's name), you would hear it consistently while in motion, rather than occassionally. Thus, i doubt it's your pads.
Hope this helps. Good Luck!


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## atoson (Dec 29, 2002)

*Re: Humming sound - caliper or wheel bearings? (427+SS_iraceporsches)*


_Quote, originally posted by *427+SS_iraceporsches* »_If you think you have a caliper sticking, then jack the car up on four jackstands, remove all of the wheels, and *manually turn the spindles*.

You prolly mean the rotor since there are no spindles in front wheel drive cars. It use a hub carrier that houses a wheel bearing which a wheel hub is pressed in and an outer CV joint is inserted through it and torqued to spec with a nut. You would also need to apply more effort turning the rotor without the wheel since the transmission is riding with the driveshaft feeling all the weight of the connected dynamic gears.

_Quote, originally posted by *427+SS_iraceporsches* »_If the caliper is sticking, you should be able to notice or feel it. 
If the brakes are squeaking when you brake, that may be slight rust, but not necessarily worn down pads; afterall brakes squeal to indicate wear while in motion, and will cease when you apply the brake, because the pads move in (farther than the squeaker) to contact the rotors to stop the car. Since the *squeaker* is designed to rub the metal and make noise (indicative of it's name), you would hear it consistently while in motion, rather than occassionally. Thus, i doubt it's your pads.
Hope this helps. Good Luck!
 
That's another first for funny names for it. We call it in auto tech school as simply a brake wear tale tab.
A wheel bearing nearing failure would be best noticed when accelerating and decelerating. As you accelerate from a stop, the pitch of the hum would be from a low pitch onto a high pitch and opposite when decelerating and always in this order. When you have a pad riding a rotor, you'd smell it and feel the drag it produces but would eventually fade since pressure isn't applied when you let off your foot from the pedal. 
A stuck brake would continue it's effect long after you've let off your foot from applying the brakes, drag would be present up until the pads retract from applied position. Rust in the pistons or pad sliders are few of the reasons it gets stuck. Other causes could be dirty fluid with solid debris in the piston sleeve area, moisture in the system which causes corrosion of metal parts, although a rusted rotor would not contribute to this since rust is removed when pads come into contact during motion.
Brake noise ussually means vibration from metal to metal contact. Remedy would be the use of antinoise blue or red compound the the backing plates of the pad. The effect would be to dampen the minute vibration which would be amplified in it's durration from the thick compound coating.


_Modified by atoson at 10:56 PM 6-21-2007_


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## Don_S (Oct 28, 2006)

*Re: Humming sound - caliper or wheel bearings? (atoson)*

One easy check you can do when driving if you suspect a wheel bearing. Get on a bit of empty road, make it quiet inside, windows up, fan off. and make some hard sweeping turns back and forth across the road. A significant difference in sound from left to right is a sure sign of a failing bearing, a bad bearing it will be noisy when it's loaded, eg: if the bad bearing is on the right side you would hear it when turning left and the sound would not be heard when turning right. 

DonS


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## atoson (Dec 29, 2002)

*Re: Humming sound - caliper or wheel bearings? (Don_S)*


_Quote, originally posted by *Don_S* »_
One easy check you can do when driving if you suspect a wheel bearing. Get on a bit of empty road, make it quiet inside, windows up, fan off. and make some hard sweeping turns back and forth across the road. A significant difference in sound from left to right is a sure sign of a failing bearing, a bad bearing it will be noisy when it's loaded, eg: if the bad bearing is on the right side you would hear it when turning left and the sound would not be heard when turning right. 

DonS

A bad bearing would be a humming noise to a rumble if it's really bad so don't confuse it from a clicking or a knocking noise caused by a bad outer CV joint which this test will conclude.


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## VeeRar6ix (Apr 5, 2007)

*Re: Humming sound - caliper or wheel bearings? (atoson)*

failing bearings hum... sticky calipers grind? not so?


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