1
Wheel Bearings
and Wheel
Bearing Service
Function of wheel bearings
• Provides a low friction bearing surface for
wheel rotation.
• Supports the weight of the vehicle.
• Transfers the lateral loads of cornering from
the wheel and tire - into the body / frame.
• Lasts indefinitely - normally the life of the
vehicle.
2
Radial loads acting on bearings
• Radial loads are forces
acting on the bearings at a
right angle to the axis of
rotation.
• The weight of the vehicle is
largest radial load.
• Jounce and rebound forces
are applied to the bearing
when the vehicle
encounters bumps in the
road.
• When the vehicle
accelerates or the brakes
are applied additional radial
forces act upon the bearing.
Vehicle Weight
Jounce and Rebound
3
Axial forces acting on bearings
• Axial loads are loads
that a parallel with the
wheels axis of rotation.
• Cornering force is an
axial loads.
• When the tires hit
curbs or strike potholes
sidewise high axial
loads are applied to the
wheel bearings.
4
Anti-friction bearings
• Bearings that use rollers, balls or
Outer Race
needles, riding between two races are
considered anti-friction or low friction
bearings.
• A rolling element, either a sphere,
cylinder or tapered pin rolls along the
surface of the races, reducing to a
minimum the friction between the moving
parts.
• A cage is sometimes used to separate
the rolling elements.
• Anti-friction bearings are lightly lubricated
by oil or light grease and do not require a
force fed oil supply system like engine
bearings.
• Some bearings are permanently
Inner Race
lubricated and sealed at the factory - and
require no maintenance whatsoever.
Rolling Element
5
Bearing types
•
•
•
•
Ball bearings
Straight roller bearings
Tapered roller bearings
Needle bearings – not used as a
wheel bearing
6
Ball bearings
• Ball bearings are suitable for
light radial loads and very
light axial loads
• Component parts:
• An inner race - with an external
groove
• An outer race - with an internal
groove
• A set of balls
• A stamped sheet metal or
plastic cage
7
Dual row ball bearings
• Dual row ball bearings are
one of the most common
types of front wheel drive
wheel bearings
• When 2 ball bearings are
placed side to side the
ability of the combined
bearings to handle axial
loads is greatly increased
8
9
Dual row ball bearings
• On most FWD cars a single
outer race housing will have
two grooves - for inboard and
outboard ball races
• Typically there will be two
inner half/races - the external
groove is machined for 1/2
the width of the balls
• A single, plastic cage holds
the balls in their proper
position and helps to retain
Inboard
grease
inner race
Outer race
Outboard
inner race
Sealed ball bearings
• Wheel bearing applications that
utilize ball bearings are
permanently sealed by 2 rubber
disks installed in a groove in the
outer race.
• These seals keep the grease from
leaking out.
• They also keep dirt from getting
into the bearing.
• This type of bearing should never
be washed in solvent.
• There is no way to repack this type
of bearing. If the grease has been
washed away by solvent the
bearing must be replaced.
10
Interference fit
• Shaft and bearing are machined for a slight
interference fit
• Shaft is typically .0005 inch larger than the hole
in the center of the inner race
• When a force of a ton or more is exerted on the
shaft the metal of the bearing will expand
slightly to allow the bearing to be pressed onto
the shaft
• In some cases the outer race is a press fit into
the housing that supports it
• This will help to prevent the bearing from rotating
inside the housing
11
Ball bearings for FWD vehicles
• FWD vehicles normally use a dual-row ball
bearings for the front wheels.
• Some manufactures used two separate ball
bearings mounted back to back.
• Since these are asymmetrical they must be
mounted in proper orientation.
• Ball bearings used for FWD cars are
lubricated and sealed at the factory and
cannot be cleaned and lubricated in the
field.
12
Cylindrical [straight] roller bearings
• The rollers have the same
from one end of the roller
to the other.
• Normally lubricated by oil but can also be lubricated
with light grease.
• Has very high radial load
capacity - but very little
axial load capacity
13
Cylindrical roller bearings
• Typically used for a rear
wheel bearing on rear drive
cars
• Since these bearings have
very little axial load capability
the axle shafts must be
retained in the axle housing
by horseshoe clips that fit
into grooves machined onto
the ends of the axle shafts
• Without these clips the axle
shaft will literally slide out of
the axle housing
• No inner race required - the
axle shaft is machined and
hardened to allow the rollers
to ride directly on the shaft
14
Tapered roller bearings
• Similar to a conventional [straight]
roller bearing except that
• Rollers have a smaller diameter at
one end than at the other
• Inner race is cone shaped - with
lips at both ends to retain the
rollers
• Sheet metal cage positions and
retains rollers onto the inner race
• Outer race has an internal cone
[cupped] shape
• Outer race is not retained to the
rest of the bearing assembly
15
Tapered roller bearings
• Have both a high axial and
radial load capacity [heavy
duty]
• Tapered roller bearings have
the highest axial load capacity
of all bearing types
• Used in heavy duty
applications where axial load
is high - such as rear axle
pinion bearings
• Best design for front wheel
bearing
16
17
Disadvantages of tapered roller bearings
• Increased surface contact area
adds strength but also adds drag
- reduces fuel efficiency
• Tapered roller bearings must be
periodically adjusted for preload
• Minor wear in the races and
rollers allow the bearing to
loosen up - permitting looseness
or wobble in the wheel
assembly
• An adjustment nut, retained by a
cotter pin is typically used for the
preload adjustment
18
Wheel bearings for RWD cars
• RWD vehicles use 2 tapered roller bearings
for each front wheel
• The inboard bearing is larger and carries
most of the weight of the vehicle
• The outboard bearing is smaller and carries
most of the outward thrust in cornering
• The offset of the rim and tire places the
center of the rim nearly directly over the
inboard wheel bearing
19
Non-driven wheels with tapered roller bearings
Inner
cup
Outer
cup
Thrust
Washer
Castle
cap
Nut
Grease
seal
Inner
bearing
Outer
bearing
Hub
Rotor
Dust
cap
Lubrication and Sealing
• The bearings are lubricated
by wheel bearing grease
• A lip seal is placed inboard of
the inner wheel bearing to
retain grease and keep dirt
out
• A garter spring is used to maintain a slight
pressure between the lip seal and the seal
surface on the spindle
• A metal dust cap [ grease cap ] prevents grease
from leaking to the outside
20
21
Wheel Spindle
Seal
surface
Inner
bearing
surface
Outer
bearing
surface
• The steering knuckle has a
spindle [ tapered shaft ] to
support the wheel bearings
• Two machined surfaces on the
spindle support the bearings
• A third machined surface is
used for the lip seal
• Threads on the outboard end
are cut for the preload adjusting
nut
• The outboard end of the spindle
is usually drilled through to
accommodate a cotter pin
Bearing retention
• Castle nuts and cotter pins are
normally used to retain the
bearings
• Some foreign cars use a split
nut with an Allen bolt clamp
• Many Japanese cars use a
special lock nut - and a square
cut groove in the spindle
• After the preload has been
adjusted the soft metal lip on
the end of the nut is hammered
into the groove in the spindle
with a hammer and chisel
• This type of nut can only be
used once
22
Bearing retention
• Inner race of the wheel
bearings fit loosely over
the spindle
– Although it is not desirable
to have the inner races
rotate on the spindle there is
very little rotation that
normally takes place
– If the wheel bearing fails
however, the spindle may be
damaged by the constant
rotation of the inner race
23
Bearing retention
• Outer races [ cups ] are
pressed or hammered
into the wheel hub
– Often the hub is integral
with the front brake
rotors
– On drum brakes the hub
is usually retained to the
drums by in interference
fit between the wheel
studs, brake drum and
hub
24
25
Wheel Bearing
Service and
Replacement
Unit type – Bearing and Hub assembly
26
• Many FWD wheel vehicles
have unitized bearings
wheel bearings and hub
assemblies that can be
simply unbolted from the
steering knuckle
• These bearings and hubs
often include the wheel
flange and wheel studs.
• The bearing/hub assembly
is normally attached to the
steering knuckle by 3 large
bolts
• The ABS wheel speed sensor is
often built into the bearing assembly.
Separate hub and bearing
• The wheel bearing
is pressed into a
bore machined in
the steering
knuckle and
retained by very
large snap rings
27
Separate bearing and hub
• When a wheel bearing needs to be replaced,
the steering knuckle will need to be removed
from the vehicle.
• A 10 ton press is typically used to press the
hub out of the bearing and also to press the
bearing out of the knuckle
– Removal of the wheel bearings is a two part
operation
• First the hub and hub flange must be pressed out of the
wheel bearing
• Once the hub and flange have been removed the
snaprings can be removed from the steering knuckle and
the bearing pressed out
28
Separate bearing and hub
• In some instances
the hub and wheel
bearing can be
removed a slide
hammer
• In other cases
special factor tools
may be required for
safe removal and
replacement of the
wheel bearings
29
Tapered Roller Bearings
• Removal
• With the wheel is removed
the dust cap, cotter pin and
preload adjusting nut can be
removed
• The thrust washer and outer
wheel bearing can now be
removed
• To remove the inner wheel
bearing the lip seal must be
removed first
30
31
Grease seals
• The grease seals should always
be replaced when servicing wheel
bearings
• If new lip seals are not available
the seal can be removed by
reinstalling the rotor , without the
outer bearing
– Thread the adjusting nut back
onto the spindle
– Pull the rotor outward - while
applying downward force at the
same time
– The rotor will come free from the
spindle - leaving the bearing, seal
and nut on the spindle
– Caution ! - if care is not used in
this procedure the wheel bearing
may be ruined
If new lip seals are to be installed
• Remove the old lip seals with a seal puller once
the rotor / drum has been removed
32
33
Inspection
• The wheel bearings
can be cleaned using
safety kleen
• Lightly polished
bearing surfaces [
satin ] is normal on
any bearing with a few
thousand miles or
more of wear
34
Examine the wheel bearings for:
• Spauling - large pits or chunks on the surface of the bearing
– Generally caused by fatigue and high mileage
• Brinelling - imprint of parallel lines on the bearing surface
– Caused by impact loading or vibration while the wheels are not turning - as
when it is transported on a flat bed truck
• Gauling - surface of the bearing appears as though flakes of bearing
material have pealed off
– Caused by overheating and / or insufficient lubrication [ or wrong lubricant ]
• Scuffing [ abrasive wear ]
– Scratches and pitting on the bearing surfaces
– Caused by abrasive material in the lubricant
• Smearing - polished edge near the outside edge of the bearing
– Caused by the bearing cup rotating in the hub bore
– Repair necessitates replacement of both the bearing and hub [ rotor ]
• Bent cage - dents or distortion in the bearing cage
– Caused by mishandling during assembly
Spauling damage
35
36
Replacement
• As a rule wheel bearings are generally replaced in
sets
• If there are any signs of damage to the bearing the
entire bearing assembly must be replaced [ inner
and outer races ]
• The outer race can be removed by hammering it out
of the hub with a long tapered drift [punch] – a small
brass drift is preferable
• Most hubs have two cast slots in the bore to
facilitate bearing removal
• Wipe all of the grease out of the bore to find them
• A special bearing installer tool is used to press or
hammer the new bearings into the hub
Packing the bearing with grease
• With the new inner bearings
repacked with grease the
hub is reinstalled onto the
spindle
• Tapered roller bearings can
be repacked by hand by
scooping up a few ounces
of grease in one hand and
dragging the open end of
bearing cage through the
grease until you see grease
oozing out of the openings
between the rollers and the
cage
37
Packing the bearing with grease
• A less messy way of packing
bearings is by way of a
packing tool that forces grease
through the cage
• Bearing packers force grease
to fill the voids between the
rollers and between the cage
and rollers
38
39
Wheel bearing grease
• Wheel bearing grease is a specialized lubricant that is
designed to stay solid at relative high temperatures
• Wheel bearing grease is sold in one pound plastic tubs
that look like margarine containers
• Chassis grease is not recommended for wheel bearings
– it is normally sold in cardboard tubes that fit in grease
guns
• Whenever repacking wheel bearings always thoroughly
clean the bearings and hubs to remove the old grease
– Intermixing greases from two different manufactures may
produce a chemical reaction between the two greases that
either turns the grease to a very thin oil [ that will leak out ] or
may reduce the greases ability to prevent friction between
metal parts
40
Coat spindle with wheel bearing
grease
41
Install rotor
Install outer bearing and thrust washer
42
Pre-torquing after bearing replacement.
• Many manufactures recommend a bearing
pre-torquing procedure
• The bearing is initially pretorqued to a very
high level - let’s say 60 lbs/ft
• It is then loosened and then properly set for
preload
• The pre-torquing helps to insure that the
new bearing is properly seated in the hub
bore
43
Adjusting
• Manufactures procedure is found in any good
shop manual
• Typically tapered roller bearings on the front
wheels of RWD cars are adjusted for zero
preload
– In most cases this means that the adjustment nut is
tightened ‘finger tight’
– If the cotter pin does not line up with the slots in the
castle nut - the nut is backed off until the cotter pin
will pass through
– The thrust washer should be free to slide back and
forth a little bit
44
45
Adjust the bearing
• Spin the rotor while tightening the nut. When a slight
drag is felt the back off one flat [1/6 turn].
Adjusting
• Some manufactures require that the wheel
bearing be preloaded with an inch / lb
torque wrench
– Typically the bearing is set to a higher level first
[ let’s say 20 ft/lbs. ] then backed off and retorqued to a lower value [ let’s say 25 inch / lbs
]
• Excessive bearing preload can cause
premature bearing failure
– Insufficient [ loose ] preload may cause shimmy,
loose steering , pulling, premature tire wear,
noise and bearing damage
46
47
Install the retainer cap and cotter pin
• When a retainer cap is used the cotter pin is wrapped
around the outside.
Install dust cap
48
Wheel bearings - rear wheels of FWD cars
• Tapered roller bearings
– Smaller but otherwise identical to tapered roller
bearings used on the front wheels of RWD cars
• Single row ball bearings
– Used on lightweight economy cars – Low load carrying ability of the single row
bearing is not an issue here since there is so
little weight being carried by it
– Usually permanently lubricated - but some
manufactures build them with an external seal
that allows them to be repacked
49
Wheel bearings - rear wheels of RWD vehicles
• 4 types.
– Single row ball bearing – light vehicles
– Single tapered roller bearing – some older domestic
cars
– Cylindrical [straight] roller bearing – domestic RWD
cars and light trucks
– Two tapered roller bearings on full floating axle –
heavy trucks
50
Single row ball bearing
• Permanently lubricated by greases
• Internal bearing seals keep out dirt & help
retain grease
• External axle seal prevents axle lubricant
from reaching the bearing
• If axle seal fails - bearing is ruined because axle lubricant washes away grease
inside bearing
51
Single row ball bearing
• Retained by a pressed on
collar on the axle shaft
– Collar must be replaced when
ever the bearing is replaced
– Removing old collar generally
requires chiseling through [ or
drilling through ] the hard steel
collar
• Bearing retained to the axle
housing by the brake backing
plate or a separate retaining
plate [ 4 bolts]
52
Single tapered roller bearings
•
•
•
•
Pressed onto axle shafts
Occasionally retained to the shaft by large nuts
Lubricated by grease - can be repacked
Seal in axle housing prevents axle lubricant from
contaminating wheel bearing grease
• Outer cup retained to the axle housing by retaining
plate [ brake backing plate ]
• Preload normally adjusted by thin sheet metal shims
placed between the axle housing and retaining plate
• Steel block in the center of the differential gearset
carries axial load from the left side axle shaft to the
right side shaft [ & vice versa ]
53
54
Cylindrical roller bearing
• Pressed into axle housing
• Axle shaft rides directly on
rollers
• Lubricated by axle lubricant
• Lip seal on the outboard end
of axle housing retains
lubricant
• Axle shafts retained by
circlips at their inboard ends
Service requires opening differential
• Service of axle and wheel bearing require
that the differential cover and differential
pinion shaft be removed first
• With the differential pinion shaft removed
the axles are pushed slightly inward until the circlips fall out - then the axles
can be removed to gain access to the
wheel bearings
• If the wheel bearing fails - the entire axle
will have to be replaced
– Since the axle shaft rides directly on the
rollers any damage to the rollers will
cause damage to the axle shaft
• Whenever servicing these axle shafts
they should be checked for spauling,
brinelling and gauling
55