At 11:57 AM 5/16/2003, Martin Bishop wrote:
I was doing my front wheel bearings last night and the inner bearing was
strange. It has been too long since I took them out so I completely forgot
what they should have looked like. The Races where not taken out when I
removed the bearings, so I just dropped in new bearings.
The thing was that the bearings do not seem to be held into place with
anything when not mounted. The repair manual says to put the cap thing
flush mount with the top of the hub carrier. If you do this it seems to
allow the bearings to move out of the races.
Is this correct? I hope so.
===============
When properly installed, the inner front wheel bearing will be kept from
falling out of the hub by the grease seal. The outer diameters of the
grease seal and the inner bearing race are the same, so the inner diameter
of the seal opening must be smaller than the bearing. The seal should be a
press fit into the hub.
The grease seal does NOT hold the bearing tightly in place, however. The bearing can move around freely. Both bearings are held in place and adjusted by the nut.
Adjustment of the nut is critical. Too loose or too tight will ruin the bearings, and this can lead to serious safety issues.
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 periodically repacking your wheel bearings. They also
both agreed that you should never use the old-fashioned stiff "wheel
bearing grease" in a wheel bearing. The grease that they both recommended
was soft, sticky, black moly grease. There are now special high-temp wheel
bearing greases that should be fine, however.
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. Grab the wheel at
top and bottom and try to shake it - there should be no perceptible looseness.
9) Firmly apply the foot brake to return the brake pads to the normal
position.
10) Repeat on the other side (once only).
Wally Plumley
928 Specialists
www.928gt.com