jpitman2

Lately on freeway trips I am hearing what sounds like a rear wheel bearing going south. Not loud or rumbly, but a light noise, speed related, echoing off the dividers of the highway, but not clear enough to be sure which side it is. I now have it up on stands - running with wheels on, I cant hear anything - maybe due to lack of real load. With the wheels off, also nothing to hear (even less load than before), but when I hold the left upright at the top, I can feel something rythmic - a tic, tic, tic... Nothing felt on the right side. Is this a reasonable deduction? Could it be something in the drive shaft ? Both were cleaned, greased and rebooted a few 1000m ago.
Nothing significant visible in the tyre treads, like a nail, or a big stone. Curiously, my initial jacking had the left side tyre maybe 1/4" off the floor, but when I started it, the tyre showed enough out of round to touch the floor - can that be normal?

thanks
jp 83 Euro S AT 55k

FBIII

Wheel bearings that are failing omit a louder noise when turning and under a greater load. If your turning to the left the right wheel bearing would make noise and vice versa.

Kevin in Atlanta

Can you isolate whether the noise is left or right? If yes, then swap the rear tyres and see if the noise follows the tires. Out of round tyre is not a good sign. How old are the tyres?

joejoe

Also the aggressive 'V' type tread pattern of sport tires seems to create the sound of bad bearing after 1/2 life. I gave away a set of bridstones as I could not even run them on my '90 944 cabriolet because they were too noisy. (they had about 80% tread left) In my opinion a terrible design.

dr bob

JP-- How many miles on those bearings? And what's the net offset (spacer thickness minus wheel offset)? 100k miles is probably a good time to think about rear bearings. They are dual-row angular ball bearings, so bigger offset numbers can affect bearing life some. And... If you find you need to do one side, plan to do both sides at the same time.


To the noise-- I'd be looking carefully at the half-shafts and CV joints, particularly if they were recently serviced. The CV joints are more likely to make a ticking noise early, and trying to hear CV joint noises with no load and the car lifted has been pretty futile for me until they are really noisy. But: The CV joint service includes removing the nut at the end of the stub shaft. That nut clamps the two halves of the rear wheel bearing together. 300+ lbs/ft is required for that, and if it is not tight enough, the bearings can be damaged. At the other end, those 10mm bolts from the inner joints to the drive flanges on the gearbox need 60+ lbs/ft. If they work loose, the inner end of the half-shaft will work around in the drive flange and give you a funny rumbling. Right up to the point the bolts get so loose that they get broken or fall out. You'll know when that happens, coasting safely to the side of some lonely desert highway in blazing heat, too many miles from civilization. (!!) At least that's my luck. Bottom line is verify the tension on the bolts and the nuts as part of your inspection/discovery process.

UpFixenDerPorsche

Hi John.

Replaced my real left wb several years ago.

Starts off as a low soft 'hrmmmmm' that you can hear in the background. Gets a bit louder over the next several thousand k's, until you can hear the volume change on left vs right turns.

Likely to be the left side as that side cops all the potholes etc., but mine looked like moisture had got in as seal looked distressed.


Fairly straightfoward to replace. (Use heat as per wsm).

Reconnecting the h/brake cable will drive you STARK RAVING &*#^% MAD!!!

Wait for a while yet for the growl to get more easily identifiable. Wheel won't fall off until growl gets really really bad for a few months. |:-\


Have fun.

John C.

WallyP

As John says, it is not likely that there will be a sudden catastrophic failure for the axle bearings, not is it really likely for a CV joint. The flange bolts can and will drop out with little warning - BTDT. Amazingly, the bolts were still in the flange when I coasted to a stop with no drive! Just make sure that those are tight, and look closely at everything else.

A mechanic's stethoscope is a very useful tool. If you repeat the "running with wheels off" test, a stethoscope might let you hear a difference from side to side - but I still wouldn't do anything until the problem is a lot more defined. You are very unlikely to cause any additional damage by waiting until the noise increases.

Any possibility of borrowing a different set of rear wheels and tires from another owner for a fifteen-minute test drive?

No, 1/4" out-of-round is not normal, and yes, it will cause noise.

jpitman2

Wow, Lots of ideas very quickly, Thanks guys. I will swap the tyres side to side and see what happens. The car has 55k mi on it. The tyres are a bit old - not doing enough driving. The hub nuts were pulled up properly with a BIG wrench IIRC when the CV joints were done, and the inner bolts are all tight, but will check them. The out of round tyre/wheel doesnt produce any discernable vibration on the road.
jp 83 Euro S AT 55k

atb

When I had a wheel bearing go out it only made noise at freeway speeds. It was not RPM dependent (never changed pitch). It made no noise when I tried to trouble shoot it with the car off the ground.

dr bob

Adam points out something that sometimes escapes us. Ball-bearing noise changes amplitude as speeds go up, but does not change pitch. So the low-frequency rumble from a bad bearing will get louder as you go faster. The design of the rear bearing is such that you may not hear the bearing noise with no radial loading. The available differences in loading angle from spacers and wider wheels also make unloaded diagnosis a little more difficult. Meanwhile, ticks from failing CV joints do change pitch with changes in road speed, as do tire tread noises.

A few years ago, Bill Ball posted a short video that showed him manually spinning the hub with the stub axle and half-shaft removed. There was a lot of noise apparent. Generally, CV joint service doesn't need to include caliper and rotor removal, but if they can be removed, a quick bearing check is easily possible with a simple spin-and-listen. The seals should provide a small amount of drag, and any noises will be readily apparent. My bearings were barely making any noise, but were fairly dry on one side when disassembled during removal. My car is pretty quiet, with quiet tires, so the bearing noises were apparent in the cabin pretty early. It took an astute passenger to notice the noises, as I'd grown up with them and didn't recognize them as odd. Like that constantly nagging ex, where you don't appreciate the level of noise until it goes away.