At 12:12 AM 3/24/01, Tony H wrote:
>HHHHmmmmmmm...ok...if the bearings are properly adjusted you SHOULD NOT be able to move the rotor? That sounds a bit harsh? Yikes! But you should be able to move the wheel.. is that what your saying?
The goal in adjusting standard tapered roller bearings on the front hubs is to have zero preload and zero end play. The bearings will live with some end play, but this will introduce looseness into the steering. The bearings will usually fail if there is excessive preload.
The best procedure is that used in the auto assembly plants.
1) Jack the car. Remove the wheel.
2) Carefully pry the brake pads away from the brake disk just enough to allow free rotation of the disk. If you pry them too far, you may force brake fluid out of the master cylinder.
3) Remove the bearing dust cap. This cap is very tight on a 928. You can use a block of wood and repeatedly tap outward on the cap, turn and tap, turn and tap, ad nauseam. It will eventually come off. Very large Channel-Locks work also, but try to avoid scarring the cap. Or, of course, you can use VW Puller 9165 on VW Tool 771, as specified in the manual.
4) Visually inspect the bearing and grease. A properly lubricated and adjusted front wheel bearing should last forever. When I was active in SAE (Society of Automotive Engineers), I had a friend who was an application engineer with a large bearing company, and another who was an applications engineer with a large oil company. They agreed that you were more likely to hurt than help by repacking your wheel bearings. They also both agreed that you should never use "wheel bearing grease" in a wheel bearing. The grease that they both recommended was the soft, sticky, black grease from Sears.
5) Loosen the Allen bolt on the locking collar. While turning the hub (keeping your fingers out of the slots in the brake disk!), firmly tighten the locking collar. As tight as you can get it with a large pair of pliers should do. Stop turning the hub, and loosen the locking collar. Tighten it as tight as you can with your fingers alone - no tools! Tighten the Allen bolt to 11 lb/ft.
6) Check the hub for free rotation - it should rotate with no sign of bearing drag. Check the hub for end float (free play) - there should be no free play.
7) Re-install the dust cap.
8) Lightly lubricate the wheel studs with a non-graphite grease, and re-install the wheel. Torque the lug nuts to 96 lb/ft
9) Firmly apply the foot brake to return the brake pads to the normal position.
10) Repeat on the other side (once only).
Been noticing some grumbling from the front area and a slight vibration
around 80mph. Decided to do front bearings. First time for me. Must say it was
surprisingly easy. Only additional tips I offer not found on the usual 928
1) a 30mm socket works perfect for punching out stuff on the smaller side of the hub
2) a 3/8" extension bar works good to punch out the other side without marring the hub if you're careful
3) use the old races with a slit cut (so now it is a "C" instead of an "O") to push in the new races. This way they pop right out after starting to seat. I used a friend's cheap Harbor Freight press, worked great.
4) Hardest part is being confident you didn't preload the bearings when adjusting the stub nut.
The 928 feels like a new car now. Very smooth. So the two main things I've done now (clutch and bearings) weren't bad at all.
The tapered bearings in the front hubs should be adjusted for zero end-play and zero preload. The easy way to do this:
- Use a socket or wrench to firmly snug the bearing nut as you turn the hub - perhaps 15-20 lb/ft of torque. This ensures that the bearings are seated and that there is no excessive grease on the rollers and races.
- Stop turning the hub, and carefully loosen the bearing nut without letting the bearing slip out on the spindle.
- Using only your fingers, tighten the bearing nut as tightly as you can.
- Check for any end-play - if there is any end-play, repeat the process, but don't loosen the nut quite so much. You must still be able to turn it with your fingers.
This method ensures no preload and zero end-play, and was used on the auto assembly lines for many years.
As a point of information - there are two types of tapered roller bearings used on cars, and they are virtually identical visually.
Those used on the front hubs must have zero preload, while those used in the differential must have significant preload. The difference is a few degrees in the taper...
The wheel bearings need to have zero end play and zero preload. To adjust the
bearings, tighten the nut firmly with a wrench or pliers while rotating the hub.
Stop rotating the hub and loosen the nut, then tighten it as tightly as you can
with your fingers - no tools, just your fingers. Check for free play - if there
is any perceptible free play, repeat the process.
On the spindles, and for future searchers/readers, I can't overstress the need to avoid over-tightening the spindle nut on tapered wheel bearings. The original cold fit is loose enough to let you -easily- move the washer with a screwdriver. Way too many folks try to fudge towards tight to get the wheel to be absolutely free of all play, but that's not the goal with cold bearings and all. The alloy hub expands more quickly with heat than the steel spindle, meaning the bearings will get "tighter" after the jut a short amount of driving and brake applications. Meanwhile, the rollers depend on having a film of grease on them to survive in service. If the cold setup is snug, the hot setup will be too tight. With no grease film, the cones will expand with the heat and spin with the excess bearing friction and reduced contact with the OD of the spindle. That wll quickly damage the spindle, most notably, as Stan reminds us, on the bottom where folks seldom look. The cascade effect is that a new bearing won't fit correctly on the damaged spindle, leading folks to tighten the spindle nut even more as they try to remove play from the replacement.
A recent Ford 4WD I owned had the two front bearings very close together, to allow room for the auto- locking mechanism for the drive system. It was incredibly sensitive to adjustment. Ford's initial WSM guidance was to tighten the nut to 75 lbs/ft to make sure all the bearing bits are seated correctly, back off the tension completely, then without rotating the hub at all, tighten the nut again to 15 lbs/ft. There were a lot of subsequent failures. The "solution" was a revised recommendation to 15 inch/lbs, only after rolling the hub and restoring the grease film that was squeezed out with the initial seating instruction. For those who didn't have access to a small enough torque wrench, guidance was revised to "finger-tip" tight. No tools, no gloves, no hand wrapped around the nut. Just the finger tips, putting the nut against the washer. Nut goes looser rather than tigher if the locking key didn't line up. For the 928, I tried the 15 inch/pound setting using a torque screwdriver in the slot in the nut, and found it a little too tight to allow the washer to move easily. So you get an idea about how sensitive the adjustment can be.
Correctly set up, wheel bearings are pretty much maintenance-free for a very long time. The only reason to open them up at all is to replace the grease that's stiffened up with age and doesn't flow as well in the cages. More bearing and spindle damage is caused by incorrect setup than by anything else including tired grease. So stay loose, stay lubricated, stay cool.
'89 S4 Auto, black