Wheel Bearing?
 

I have had a bit of a whine from the back for a while, but mainly noticeable on longer drives. Usually it seems to come from the right, but this weekend on a fun run I thought it was from the left. Up till today, no real worries, but figured it should be looked at sometime.

Today, after a 25 km (~15 mile) drive, coming off the highway I noticed a scraping sound, much like an excavator scraping on rock. Stopped, the noise was gone, slight rev of the engine, no noise. Pull away from the stop, on a slight uphill, and the noise is there and then disappears. Gas up and then home, I decided to check the wheel hub temperatures. 126°F on the driver's side, 138°F on the passenger side, and about 121°F on the fronts. All the calipers read about 119°F.

I decided to jack the car up (because I can:) ) and see what I could find. No stones or evidence of anything grinding between the back plates and discs. The brake pads look good. No excessive play, at least to my feel on either wheel. The discs appear to be slightly warped, but not excessively (there is a bit of drag on both on one side) - probably as a result of setting the parking brake after a spirited track drive. Rotating the discs with the wheels removed, the passenger side sounds slightly noisier, but nothing that I would call excessive, and I can't feel it as being a bad bearing.

So now I am debating - do the passenger side bearing as a guess ( I'll need to acquire a puller I suspect, but that is not necessarily a bad thing), take it to a mechanic (probably the dealer) or ignore it and take it for another drive? I hate changing parts on the basis of guessing and gut feel.

How many miles or km are on the car?

107,500 km (~67K miles). As far as I know, the original wheel bearings. I bought it used 4 years ago, I believe I am owner number 3. The engine was replaced at 73,000 km in June 2013, then I bought it in November when the guy traded it in on a 911. I never did find out the reason for the new engine, but figured since it is not a collectable, a newer engine with non-matching VIN didn't bother me. The service records I have from the dealer, which do not cover the entire life, show no wheel bearing replacement.

On a side benefit when checking out the issue today, I found two stubs of brad nails in the rear rubber, both about 1/4" long. They went in shallow, and have not punctured through the tire.

Get the car up to speed (100 mph) on the freeway for about twenty minutes using the brakes as little as possible. Coast off the road and and carefully reach into each wheel and check the hub temp. If one hub is hot, suspect the bearing.

Take off all the wheels and put a stethoscope on each hub and rotate. If you have a bad bearing it will sound different from the rest.

Wheel Bearings
 

I had one go out and I drove myself crazy trying to decide which one....best answer is replace both sides at one time. Also use a good quality bearing Like FAG or Timken...avoid cheap chinese bearings that seem to good to be true on price......they are.

You can pull them in place after removing the axles

Just went through this on my car at 133K miles. I'd replaced rears at about 120K after hearing noise...all good.

Sounded like front passenger side but always hard to tell. Replaced bearing and still had the noise. Figuring I had the wrong side, I replaced the drivers side...still had the noise. Couldn't believe it!
Replaced front tires and noise went away... REALLY couldn't believe it!

I had no tell tail signed that pointed to tires, no hopping or vibrations, didn't change with temperature...nothing.

Oh well, all bearings are fresh and tires are new!

There are many shops that offer free inspections, I suggest you go to one and have them check it out and if you don't want them to fix it just pay the $30 or so hoist fee. It is very easy to diagnose a bearing on the hoist by just driving the car with the wheels in the air. Wheel bearings are tricky to diagnose from inside the car at times and there have been many times that I was convinced it was one side when in fact it was the other.

Hub bearings wear us usually easy to diagnose. If the noise is there when turning one way and not when turning the other way it is almost certainly a hub bearing. Of course if bearings on both sides are gone there will be noise turning both ways, but that is quite rare. They usually go one at a time. The bearing will be fine and wear slowly until reaching a specific point of wear and then go quickly.

Right, by loading each wheel by sharp turn and acceleration/ deceleration, you can pretty much reproduce noise and ID bad bearing.

My right rear bearing became noisy at 69K miles, noticed shortly after I bought the car. Sharp left turn with full throttle induced more noise, but hard to hear with top down. It was apparently original bearing, German made FAG and when I took it out and apart surprisingly one ball was missing in the bearing, and the inner lace had scoring/ dent.

I replaced both sides with FAG bearings but one was slightly smaller in OD so that after press-fit it was still loose in the bore and I could move it by hands without heat... I bought a few more to sort out just in case and they were dimensionally comparable to the original bearings so I got spares for front end later. It only costed like $35 each but FAG quality deserves better...

I wish I can find road around here to safely do 100 mph for 20 min... Next time I get pulled over for speeding I'll tell the officer that I was trying to monitor bearing temp rise for diagnosis!

There are a few You Tube videos where they remove the seal from new Porsche FAG replacement wheel bearings and find one side not greased. So, instead of buying $39 FAG bearings from Pelican, I purchased $54 Timken bearings for my Boxster from Rock Auto. Guess what? Packaged inside the Timken boxes are FAG bearings. Rock Auto says it is normal practice for a supplier to repackage another supplier's parts, and they are not concerned that they charge 40% more and misrepresent the part. The solution seems to be to take them apart and re-grease them before installation. I didn't want to watch football tomorrow anyway...