Barry A. Waters

Folks,

After searching previous posts I can't find an answer so here goes!

While moving forward faster that 20 ~ 30MPH, the car has recently begun to generate a 'humming noise' (like a B-17 is flying nearby). The noise is NOT engine related and is confined to whatever is rotating at (or above) the above mentioned speeds when the engine is at idle. Wheel Bearings?

It is NOT the tires as I've swapped all four as a test, although it does sound like a noise a tire(s) could generate. It’s probably a good way to imagine the sound though. Just like "HUMMMMM". No clicking or ratcheting, just "HUMMMMM".

Also note that the noise does appear to come from the right-side of the car and not the left but I and my passenger(s) can't determine if it's from the front or the rear. I pulled the wheel caps off the Fuchs, drove 30 miles and then checked the temps around the hubs and nothing stands out: average of 96 Degrees F on both front grease caps and an average 102 Degrees F on both rear stub axles so I've got NO obvious temp readings.

I CAN momentarily make the noise go completely away by steering to the left. As soon as I return the steering to straight-ahead the noise immediately comes back. If I steer to the right the noise stays the same or may even seem to get slightly louder.

I've adjusted/re-packed the Front WBs and on the jackstands they essentially rotate forever with a good hand-forced spin and with no noise at all (no idea how old the bearings are however). I also feel nothing loose when I grab the left or right Wheel/Tire assembly and move it back & forth. ARGHHH!

The CV Joints/Rear Axles on both sides are only a few years old w/good boots (inner & outer) so they should be fine. With the rear off the ground both sides rotate with a similar SLIGHT noise. I have no idea how old the rear bearings are.

So, I'm mystified - especially with the 'slight turn to the left eliminates the noise' thing.

Any thoughts?

Barry
HELP!!!

rusnak

Generally speaking wheel bearings make a humm noise and CVs make a clicking sound when they are going out.

I'd say it's a wheel bearing, not knowing more at this point. You can grab the tire at the TOP (not side) with both hands, and try to rock the wheel top to bottom. If you feel a large clunk, then you know that bearing needs service. On the rear, you can put your shin against the rear bumper and try to shake the car side to side while looking at the rim. If it moves at all, the rear wheel bearing needs to be changed.

jakeflyer

The hope would be the front end. YOu can take a passenger and get up to 35mph. Go into neutral, turn the key off (and then turn the key back on after the engine is off so that you can steer) and have the passenger stick his head out the window and try to hear the sound. PUt the rear end of the car on jack stands and put the car maybe into 1st or 2nd and let the rear spin w/o gas while the passenger is besides the car and go to each side to listen. IFFF you do this DO NOT DUMP THE CLUTCH, feather it out to see what happens. If you packed the front, you can pull the the wheel off when the nut is off the spindle. The outer bearings can then be inspected. (I assume you know what to look for??). The inside bearings may require removing/replacing the seal to look at them. Are the CVs torqued down to spec. They are a bitch to do, and they take like a zillion pounds of torque, but it is something you should check , if you cant id the noise. I assume the tranny is full of oil??
BArry

TT Oversteer

I had a wheel bearing wear out on a previous car. It was a VW Jetta that had 165k on it before "the noise" started. It was just as you described. I wasn't flying formation with a B-17 but there was a definite chassis-speed dependant rumble that went away when side loading the wheel in a turn. Although a different car, it was front wheel drive with CV joints and axles similar to the 911. You haven't given us the mileage of your car. If you are in the 160 to 200k range I would bet on rear wheel bearings.

rusnak

I had to replace a wheel bearing this summer. Not fun. The hardest part was getting the stub axle out. I had to use almost every tool in my garage. On the bright side though, I have this pro quality, high dollar puller now.

If it's a rear I almost recommend taking it to a shop unless you are fairly brave and highly motivated.

Daniel Dudley

Generally speaking, when you steer to the left, you are loading the right wheels up, so it is probably a left wheel bearing. Fronts are easy to pull and regrease, and it is not too hard to pull the seals and replace them. Tapered bearings are very easy to inspect clean and service, and you should check them out even if they seem fine. Rear bearings do not have to be replaced on both sides if only one is bad.

Good time to get a Bently manual, or 101 projects for your 911. I believe that you would enjoy that book, as it is a hands on primer on 911 basics.

BlackPearl

Wheel Bearings?
Trans bearings?
CV joints?
Brake Rotors warped?

Not to give a scare, but I experienced a similar "humming/drumming" sound about a year ago. Did the whole "bearings/CV's" thing. Nope. Turned out to be the middle bearing assembly on the output shaft of the trans. OUCH! Before checking the main bearings, they did pull the "nose-cone" off the trans to check the assembly inside it ... which can get noisy, and is less $$ to fix.

On the positive: I experienced noise and vibration from the front of the car just recently. I did the bearings thing again, this time in the front. Nope. Tunred out to be slightly warped brake rotors. (I should have been clued-in by the "blue-ing" of the rotors after the last track event ... but no.) So, I replaced the rotors and pads up front. Bingo! Quiet and smooth again.

So: check the rotors for blue-ing/warping. Check the brake pads for thickness. You can spin the front tires when off the ground and see if they come to stop with a sudden "bump." If so, a clue to slightly warped rotors. You can try rotating the rear wheels, but the trans may cause a bit more ffriction through the R/P assembly. Check the rear pads and rotors. Frequently they are skipped during inspections since rear brakes "wear out much slower."

Hope that helps, and good luck!

wwest

Replace the stuck brake caliper/piston.

Amber Gramps

My guess.....the outer right rear bearing....

Ed Hughes

I'd argue that it is NOT the LH bearing, but the RH bearing. When a bearing starts to go, typically putting pressure on it will quiet it down.

Barry A. Waters

Folks,

I'm really liking the RR WB diagnosis. The car has approx 230,000 miles on it. The transmission possibility makes me gulp but I 've got my fingers crossed on that one! I will check the trans fluid level tomorrow however - GREAT call!

Front WBs should be fine, I rebuilt all four calipers & replaced all brake hoses & rotors a couple of years ago so that should be ok (rotor temps are fine, pads are great and braking action is spot-on).

Complete CV Axles on both sides were also done a couple of years ago with quality stuff and appear fine as well.

Yeah, I'm liking the RR WB diagnosis a lot! It will all come to a head shortly and I'll post the results. Thanks for all the great input!

Barry

old man neri

I would still check out the stuff mentioned (brakes..etc) a lot can happen in 'a couple of years'.

Ed Hughes

Agreed!

Green86Cab

Will the noise go away if you put your foot on the brake pedal very lightly?
I had a similar noise on my 86 and it was the brake pads vibrating. The PO had changed pads but not surfaced or replaced the rotors - the pad was sitting in a groove.

stealthboy

I had a similar noise on my 1986 911 and it turned out to be the front passenger side wheel bearing. I replaced both front bearings myself; wasn't too bad.