rear wheel bearing noise?

[jmohn]

The car is a '78 SC.

I'm hearing a dronning (reminds me of knobby snowtires on bare pavement) coming from the rear; the sound goes away during sweeping left turns. Probably rear wheel bearing; I'm just looking for some corroboration before I start taking things apart. The last car I had with a bad rear wheel bearing (Chevy, 30 years ago) sounded more like a growl than this does.

Thanks,

Jerry M
'78 SC

[HunterVonWurst]

What is the condition/age of your tires? Worn, old, hard lumpy tires make all kinds of noises.

[Gunter]

Lift the rear, grab the wheels at 12 and 6 o'clock and rock. Should be no play.

Check that the CV-bolts are tight.

[verdeboyo]

hello Jmohn
I had the same droning noise on my Carrera. It was a light drone that seemed to get louder as time went on. I had the one side done, then months later the other side went, so I knew it was a bearing thing. I got my bro, being a BMW tech, but he took the trailing arm off with the hub, so he could press the old one out and press the new one in. When the wheel and disc is removed you'll be able to feel the notchyness of the bearing as you turn it by hand, that'll show you it's def good for the bin.
It def ain't the tyres unless you got tractor tyres on the rear, surely to be the wheel bearing. Best to get both sides done if you can. Over here in uk the bearing is £40 genuine porsche. While it was all in pieces I had to replace the handbrake components in the hub cos some o the springs were f***ed. Got a little help from some o the members here.

[don gilbert]

G's advice about rocking the wheel is good, but i couldnt get mine to rock and was having the exact droning noise, which would quit during a rt. turn. Turned out to be the rt rear bearing. Good time to replace the bushings to. Was an all day job to do both, with my brother helping, and we kinda know what we are doing and had all the tools..

[CCM911]

Agree that it would not hurt to change the bearings. But unless you plan to replace all of your suspension bushings, you do not need to remove the trailing arms. Just find somone who has the bearing tool.

[jmohn]

Thank you, gentlemen, for the feedback.

I do intend to lift the rear and try to "wiggle the tire" (I did try moving the rear of the car to see if the rim moves, inconclusive), but unless the bearing is really worn it may not show as "loose".

CV bolts are all tight, tires are only one season old and not badly worn, but most importantly I can make the noise go away if I turn left (even swerving gently on the road will make the noise go away every time I swerve left).

Guess it's time to order a set of rear bearings, I don't the "special tool" but I have done this type of thing before (on other equipment not a Porsche). It's just a matter of heating the hub, chilling the new bearing and assembling the the proper pieces to pull and push on the appropriate portion of the bearing as you're removing and reinstalling.

I do need a big socket for the stub axle shaft nut. Could anyone verify the '78 SC uses a 32mm nut on that shaft?

Thank you,

Jerry M
'78 SC

[sc_rufctr]

The best way to check is...

Jack the car up and remove the wheel.
Undo and relocate the inner CV so that the hub is completely free. (78SC)
If your rear brakes drag? Remove the rear brake pads and make sure the hub is not dragging on the hand brake shoes.
Then reinstall the wheel and sung up the wheel nuts....

Spin the wheel by hand and listen/feel for worn bearings.

Take your time when doing this and try to asses the condition of the bearings by listening and feel.
It's not hard to do but takes a little finesse.

Have a beer by your side and wait for a quiet moment as your turn the wheel faster and then slow. If they are worn you'll be able to hear them when turning. If they're good then they should be silent... Even a very slight rolling noise is signs that they are gone.

Grabbing at 12 and 6 and pulling top and bottom is also a good idea but I've often found noisy/faulty bearings that had no play when tested like this.

[James Brown]

Also, try pulling on the parking brake when going forward slowly, this re sets the brake linings as sometimes this causes a grinding or low rumble. Just to rule out anything that's not the bearings.