loud hum, wheel bearings?

[mjfeeney4]

Before ordering parts to replace the from wheel hub(s), I was wondering if this sounds ( no pun intended) like a worn wheel bearing. What can be best described as a loud hum, similar to aggressive tread off-road tires used on trucks, has been comming from both sides of the front end. Getting progressivly loader over the last 6-12 months. The 91 525 has 164K mi. No relationship to engine RPM, and no difference on various road surfaces.

Other posts describe a sound that is louder when turning (at higher speeds), but mine has no grinding sounds and no difference with turns. The sound does get louder with high speeds, and it is almost inaudible below 25 mi/hr.

Befor ordering from BMA, do others agree that the bearings are shot??

[Rory535i]

yeah definately the wheel bearings.

[mjfeeney4]

yeah definately the wheel bearings.
Nothing worse than fixing the wrong part. Appreciate the feedback.

[mjfeeney4]

Jacked the rear end so the wheels could spin freely and the noise is coming from the back end. It is difficult to tell exactly but it appears the passenger side is louder. Any ideas on how to tell if the problem is the rear differential or rear wheel bearing. One clue is that the hum is more noticable from the inside of the car, than the outside.

Mike Feeney



Before ordering parts to replace the from wheel hub(s), I was wondering if this sounds ( no pun intended) like a worn wheel bearing. What can be best described as a loud hum, similar to aggressive tread off-road tires used on trucks, has been comming from both sides of the front end. Getting progressivly loader over the last 6-12 months. The 91 525 has 164K mi. No relationship to engine RPM, and no difference on various road surfaces.

Other posts describe a sound that is louder when turning (at higher speeds), but mine has no grinding sounds and no difference with turns. The sound does get louder with high speeds, and it is almost inaudible below 25 mi/hr.

Befor ordering from BMA, do others agree that the bearings are shot??

[niall]

the diff is a possibility but i think more likely wheel bearings, they are a cheaper fix aswell!!!

[Mobius]

A hum related to the differential or the CV joints would most likely be more noticeable when you're on the gas. If the hum is only relative to rolling speed and sounds no different when accelerating hard, it is most likely a wheel bearing.

Get someone to stick their head out of a passenger side window and see if you can comfirm that its coming from the rear. It seems like rear bearings are a bit longer-lived than the front.

I've got a front hub/bearing in the mail right now. Now I have to figure out how I'm going to measure 214lb/ft of torque.. :\

[mjfeeney4]

Futher tested by jacking only one side of the rear and the problem now appears to be isolated to the rear passanger side. I should have included that the noise started with the dreaded ticka ticka ticka sound about 1 year ago, but now has been replaced by the hum.

The sound does not appear to be effected by engine RPM or transmission gear, only the speed of the car.

Have I limited the source to rear wheel bearing?

Mike Feeney

[Mobius]

Futher tested by jacking only one side of the rear and the problem now appears to be isolated to the rear passanger side. I should have included that the noise started with the dreaded ticka ticka ticka sound about 1 year ago, but now has been replaced by the hum.A 'tick' would be less likely a wheel bearing and more a CV joint.. Check your CV boots back there for any tears or leaking.

Still, if it was a CV joint issue, it should change with torque. Also, failing CV joints don't typically 'hum'.

If the boots check out, I think you're safe to assume it's the bearing.

[atomicDog]

I'm having a similar problem with my 1995 525iT. I'm planning to replace the front wheel bearings on my car soon, as they have over 141,000 miles on them.

Anyone know what size socket is required to remove the wheel bearing retaining nut?

[Mobius]

I'm having a similar problem with my 1995 525iT. I'm planning to replace the front wheel bearings on my car soon, as they have over 141,000 miles on them.

Anyone know what size socket is required to remove the wheel bearing retaining nut?
http://www.bmwe34.net/e34main/maintenance/suspension/wheelbearing.htm

[Mr. BILL]

Does the noise go away when you change lanes at speed? Usually wheel bearings get louder when you put a load on them and quiet when you unload them.

[mjfeeney4]

The hum does not appear to be effected by lane changes or turns. only effect is speed of the car, no change with engine RPM or transmission gear.

[632 Regal]

All in all, dont forget to rotate the tires prior to changing the wheel bearings. A lot of troubles with tires can cause the same sort of noises. Ryan went through several rear end fluid changes and was looking at the rear end being replaced or wheel bearings when he discovered it was the tire. The wheel bearings are pretty hardy on these cars so dont overlook the simple things first. Use the spare tire for the side in question first.

Just my 2¢

[mjfeeney4]

Changed rear diff fluid, no noticable effect. Hum is present with the rear end jacked and there appears to be some vibration which is not noticed when driving. Noticed that the sound is much less in a left turn, does this suggest the rear bearing (right side?). Also the sound is present with either the right rear or left rear jacked up separately.

Been reading the archives and several people reported rear end noise caused by a worn center bearing or transmission mounts.

[Claude]

Changed rear diff fluid, no noticable effect. Hum is present with the rear end jacked and there appears to be some vibration which is not noticed when driving. Noticed that the sound is much less in a left turn, does this suggest the rear bearing (right side?). Also the sound is present with either the right rear or left rear jacked up separately.

Been reading the archives and several people reported rear end noise caused by a worn center bearing or transmission mounts.

Michael what did you finally discover being the cause of your noise problem ? I am interested because i presently have the same symptome on my 535i 89.

[tim]

I'd check the center bearing. Theres a rubber boot thing that isolates the bearing itself from the housing. There may be nothing wrong with the bearing itself, but you have metal to metal where this rubber boot is worn, and you pick up driveshaft sound through the frame. Wheel bearing failure is obvious when the car is jacked up and the hub is checked for play. Not only that but the noise will steadily increase until it is howling as you drive. After that I'd check the driveline coupling (the rubber thingee). If those checked out I'd take a real good look at the CV joints.

[M20Turbo]

Very interesting thread, I'm having smiler nosies, even after I replaced the front wheel bearings, rotors & pads..... I will check the drive line for possible worn parts (center bearing, flex disc, driveshaft guide bushing, or maybe it's the vibration damper?) with just over 200K miles on the car I'm sure more than one of those parts if not all need to be replaced.

[Ross]

I'm with 632 Regal on this. I've been fooled myself into thinking there were bearing problems when it was tires making noise. Old hard ones will do it as will tires that are feathered, not that any BMW would do that.

[Claude]

I'd check the center bearing. Theres a rubber boot thing that isolates the bearing itself from the housing. There may be nothing wrong with the bearing itself, but you have metal to metal where this rubber boot is worn, and you pick up driveshaft sound through the frame. Wheel bearing failure is obvious when the car is jacked up and the hub is checked for play. Not only that but the noise will steadily increase until it is howling as you drive. After that I'd check the driveline coupling (the rubber thingee). If those checked out I'd take a real good look at the CV joints.

This noise / hum started for me last winter when running with snow tires, noise at that time seems to me (from the driver seat) coming from the front right wheel. Since than i passed to summer tires but still have the same noise (no difference); so my tires should'nt be the cause of it.

A bit of rust on the edge of rear disc / rotor seems to touch those disc's protection shield (sheet) this was fixed with minor change, the main noise still there.

Lately i sat myself on the rear seat when someboddy else drove the car, from there the noise was much louder and it appears that it's coming from the rear end of the car not the front !!

If we exclude wheel bearing, is it really possible that a defective drive shaft central bearing generate this noise and this one be transmit to the car frame via rear suspension elements ?

This central bearing being under the exhaust system and under a metallic shield is there a way to clearly say if it's or not the cause of this noise / hum ?

Could this noise be generate by the differential itself ? I notice that after a long trip the differential is hot (i an stand my hand on it) when can we say that heat level is abnormal ? My 3 oil seals have been changed last year, no trace of oil leak, oil level ok.

I don't want start replacing the central bearing to found out that the noise source is somewhere else ! I am seeking a way to pin point for sure the noise source, before starting to change pieces.

What's your thought

[tim]

My thought is that if it was the diff, there would be a marked difference in the noise under accelleration versus say coasting or cruising. I would also think that, like a wheel bearing, it would be louder when turning. It is normal for the diff to get hot. It's cheap and easy to fill it up with the Mobil1 70-90wt which is spec, and even if the diff were on its way out, you would hear some temporary improvement. You said you r&r'd the fluid, so that probably isn't it. If the subframe bushings are worn through, perhaps you are picking up normal diff noises through the frame.

The center bearing and the flex disk usually go together. The flex disk wears, placing more lateral stresses in the drive line, causing the rubber boot (or grommet or whatever it is) around the bearing itself to wear faster, and eventually some part of the bearing touches metal. Then you get what is variously described as a hum, with a faint ringing to it. This is the frame amplifying the sounds of the driveline. It's a pain to drop the exhaust, but a quick visual inspection should be enough to id the problem. It happened on both of my e34 540's at about 80k mi. I've got rabbit ears for car noises, so I bet alot of people drive on for a long time just used to the noise. Eventually, they will start to hear the clunk of the shaft hitting the mount when accelerating, and their flex disk is toast by then.

Personally, I try to id problems in ascending order of expense. First thing I'd do is open up the rear brake calipers, bleed a little fluid, and make sure they're not grabbing. Next, I'd rotate the tires around and see if there's a combo that stops the noise. While doing that I'd check each hub for play and eliminate the bad wheel bearing possibility. I'd closely inspect the subframe bushings, to make sure they hadn't knuckled causing metal to metal contact. Then I'd drop the exhaust and inspect the driveline as suggested above. Finally, I'd get a qualified opinion on my diff and CV joints by a specialist. Failing all that, I'd get a louder stereo ;)

[bbig119]

I've been having a noise that I have wanted to blame on wheel bearings, but can't say for certain. The noise is not always reproducible. The sound is a repetitive squeaking sound as the wheels turn. The sound does not seem to be affected much by speed and load on the wheels while turning/changing lanes can make the sound more pronounced-- but only if its already making the noise-- I only hear the noise maybe 15-20% of the time. It seems the sound is loudest from the passenger side rear.

I need to get under the car and check things out, but haven't had the chance. Could this be wheel bearings?

[bmwpower]

My thought is that if it was the diff, there would be a marked difference in the noise under accelleration versus say coasting or cruising. I would also think that, like a wheel bearing, it would be louder when turning. It is normal for the diff to get hot. It's cheap and easy to fill it up with the Mobil1 70-90wt which is spec, and even if the diff were on its way out, you would hear some temporary improvement. You said you r&r'd the fluid, so that probably isn't it. If the subframe bushings are worn through, perhaps you are picking up normal diff noises through the frame...

Which diff does he have - open or LSD? 70w-90 isn't spec for an LSD...75w-140 is.

[bmwpower]

To see if it's definitely wheel bearings, I would:

- jack up the car on stands
- remove the rear wheels
- remove the axle shafts
- remove the caliper, pads and caliper brackets (hang the calipers from a stiff wire)
- reinstall the wheels

Spin the wheels and see if you hear the sound or feel something dragging. If the bearings are good, you should hear nothing since you've essentially isolated everything. The wheels should turn smoothly.

The last thing I would check if the above tests fail:

- remove the rear wheels again
- remove the rear rotors
- check/remove the parking brake pads
- reinstall the rotors
- reinstall the wheels

Spin the wheels once again to verify if the sound was the parking brakes dragging.

I've seen parking brake pads peel off from the pad surface in spots causing dragging.

[TomG]

Consider the possibility that the output shaft bearing is toast on the RH side of the diff... had the same noise in my 525iT, changed front wheel bearings with no improvement. Does the noise decrease when cresting a rise in the road, unweighting the rear end?