rear wheel bearing questions

[pmajka]

1988 Carrera, 131,000 Miles

The rear bearings are either origional or 10 yrs old.

When should they be replaced?


Problem: audible drive line speed, thrumming oscillation between 40MPH and 65MPH.
This is after smacking rear wheel in to a curb at 45 (degrees) doing bout 30MPH. Tire is fine, balanced, rim is straight (needs paint), but you can hear it. Friend was outside car and could hear it.

advice? do both?

[haycait911]

if you can eliminate tire noise and trans and the thrumming is still there it's probably the bearing. I'm in collision repair and on most hits like you describe we're putting in new bearings. it doesn't take a very big bump to put them out of true. porsche wheels are so strong it takes a lot to bend them and the bearing is the next weak link. Don.

[randywebb]

Rear Wheel Bearing Tests:
Rear Wheel Bearing Tests

Removal:
Rear Wheel Bearing Removal

note - your car may differ as it's a late model

Collected Miscellanea:
A. When?
Check wheel bearing tightness at each oil service.

When I change rotors, the hubs have to come off so that's when to grease & inspect the wheel bearings.
Mileage: anywhere from 30,000 to 80,000 miles has been quoted by various authorities

B. Inspection in situ
Spin each front wheel by hand. If a light grinding noise is heard an inspection of the outer bearing on that wheel should be done. If the outer bearing is failing you will be able to see tiny metal chips stuck in the grease between rollers. At that point the bearings should be replaced ASAP.

With the weight of the car on the tires, if one grasps the top portion of one of the tires and alternately pulls outward - pushes inward with some force, there should be no "free play" or any clunking.

[randywebb]

more:



I. Adjusting Wheel Bearings
http://forums.pelicanparts.com/porsche-911-technical-forum/252065-front-wheel-bearing-replacement-post2248641.html#post2248641


My reason for starting this project was that bearings I thought were adjusted correctly using the standard method were producing heatbeyond which I thought was appropriate. This was not caliper/brake pad heat showing up on the rotor, but heat from the bearing housing. Not being one who like subjective measurements (I use a dial gauge on my valve adjustments as well, eliminating the "feel" portion of the adjustment). So, this is an attempt on my part to produce more reliable, reproduceable results. I understand your concern on the "looseness" of the bearing. I have found, however, that this measurement gives a washer that responds to lateral pressure as it should.

I used to think that the proper way to adjust these washers was to lever the screwdriver against the bearing housing and try to slide the washer to see if it was tight enough. When I learned that the movement of the washer was to be just by the action of the screwdriver against the washer and just pressure from your hand (not levered against anything) I realized I was setting things too tight.

I know this is a radical approach - don't try it unless you think it will improve your chances of getting an even, proper torque on the wheel bearing. If you feel that 5 thou is too loose, use 3-4 but from my experience, I've had good results with 5.
Just an idea, if you like your current adjustment method, stay with it. I just think it's a good idea to check for heat in this bearing assembly after you've installed new bearings or repacked you old ones. You could probably use the magnetic stand with flexible arm to mount the dial indicator but I felt that the rigid frame would give more predictable results.

Another trick most of you probably already know, leave the allen head wrench in the nut for the adjuster to make your small adjustments for tightness- you can just turn the rotor slightly the appropriate direction, it will tap on the allen wrench and rotate the adjusting nut in whatever direction you need. Easier than tapping on the nut with a screwdriver and hammer to rotate it.

To Adjust:
Make sure you adjust the bearing properly. Tighten the collar nut so that you can slightly move the thrust washer under the nut with a flat blade screwdriver by pushing against it. But don't leverage the screwdriver against anything. Then tighten the allen screw to lock down the collar nut .

Too tight, known as preload, is worse than too loose, and will lead to failure much sooner.

The one step which is most important, and is oft overlooked as to its significance, is to spin the wheel whilst tightening the castle nut until the wheel starts to slow from the friction. Almost tight enough to keep the wheel from turning. This is the torque setting step Walt's buddy referenced. In this step you are assuring that all the bearing components (both cones) are properly seated and aligned. Then you back that funny nut off about 1/3 of a turn til the thrust washer can just be moved with your screw driver.

And while we are at it, please don't fill the dust cap with grease. None. Zip.

[pmajka]

just started to check the fronts.

So with the WAsher being able to move under the Force of the screwdriver, with out leverage, I have a little clunk (little little).

When little little clunk goes away, i cant move the washer...too tight?

[pmajka]

FRONT adjustment...got it...
now for test drive. betting the overall problem is the rear.

[pmajka]

Yep noise is still there. even when in neutral, going 40 and cut the engine.

So, How much is getting a rear bearing replace gonna hurt $$?

[kepperly]

If you are replacing the rear wheel bearings on an 87-89 carrera,
you are in for a job. I had to make special tools, etc. to even attempt it. Remember when you remove the rear half shafts on
a g-50 CAR, the outside axel stub is a part of the half shaft and has to come out to replace the bearings. This will usually destroy the bearing and at the same time you really should replace the half shafts which are not serviceable, at least the outside c/v joint isn't. When you find out what the dealership wants to replace please post.

Keith Epperly
87 slant nose turbo look carrera cabriolet

ps do you have the capibilities to torque the rear axel nut to 380 plus ft. lbs.?

[pmajka]

Ohh, had a thought...not a good one either.

Could i have bent the half shaft from the impact??

I just had both half shafts replaced recently too.

[kepperly]

possibly, but more of a chance they screwed up the bearing while replaceing the half shafts. It would be very hard not too.

Keith Epperly
87 slant nose turbo look carrera cabriolet

[pmajka]

FWIW...it was rear wheel bearing. as soon as wifey gets a job, i will get the other one done for good measure.

[cbeers]

Hey Keith,

I have seen you post this before and I still don't understand what you mean. I have replaced both of my axles/half shafts on my car and neither time did I have to deal with the rear wheel bearing.

I took off the 32mm? axle nut and the inner bolts on the transmission flange and the axle came out like butter.

educate me please

-Chris

[kepperly]

CHRIS ,
WHEN I REMOVED MY HALF SHAFTS THEY PULLED THE INNER
BEARING AND SEAL OUT WITH THE AXEL STUB. I COULD OF DONE IT THE WRONG WAY BUT THAT THE WAY IT WAS DETAILED IN
bENTLY MANUAL.

KEITH EPPERLY
87 SLANT NOSE TURBO LOOK CARRERA CABRIOLET

[Eric_Shea]

Terminology:

Hub - Round thingy with the studs on it.
Stub axle - Attaches to the outer CV and goes through the hub/bearing and is fixed with a 36mm castle nut on the hub.
Axle - The long thingy with the CV's on it

Chris, as long as the hub remains in the bearing you won't have any problems with a good split bearing. Removing the "hub" from a split bearing ruins it.

Keith, that happens often. What he's saying is; When he removed his "hubs" the inner race stuck to the hub and the split bearing came apart.

Keith again, if you're simply replacing the stub axles and the actual axles with the CV's, there's no real reason the bearings would be screwed up... you basically never touch them in that application.

[cbeers]

Eric, many thanks. This has been perplexing me for a long time now since this has come up a few times over the last few years and each time I wonder why mine were so easy

I love learning on this forum!

-Chris

[kepperly]

Eric,
Are you aware that the g-50 carrera series has the axle stub as
a non removable part of the half shaft. The outer c/v's are not serviceable and when the stub axle is forced out it takes with it the inner bearing and seal. I simply replace the inner and outer bearings and races at the same time, "since I'm in there"

Keith Epperly
87 slant nose turbo look carrera cabriolet

[88-diamondblue]

I had both my axles out this last summer and the axles came out without any issue with the bearings. Remove the axle nut, dropped the bottom shock bolt and they slid right out. Have driven 700 miles and a full track day with no problems. I was also confused with a problem with the bearing. Also, on the G50 the outside CV can be taken apart and cleaned but not replaced like the inner CV.

[rusnak]

nevermind, just saw the diagnosis

[Eric_Shea]

Keith,

My apologies. I didn't realize they made 911's past 73!

In all seriousness, no, I wasn't aware of that arangement. Do tell, are there two bearings in a later model car vs. a split bearing? The picture Michael posted shows a shiny face on his stub axle. I'm assuming there's an inner bearing there and an outer bearing for the hub now?

[cbeers]

I am with Michael, mine came out with no issues at all.

Again, though, I only took out the axles, nothing to do with the hubs or bearings at all......

-Chris