Reasons for Bearing Failure



AMSOIL synthetic greases provide superior protection for

bearings.

Worn-out bearings can usually be blamed on either inadequate lubrication or improper

installation or adjustment, and it is important to pinpoint the reason for failure before

starting repair procedures. The bearings on the passenger side of a vehicle often fail

before those on the driver side because they are exposed to more standing water in the

gutter.

In order to harden the metal, most bearing components are heat-treated. However,

because heat treatment can only penetrate so far into the metal, spalling becomes a problem

once bearings wear to the softer metal underneath the heat-treated layer. Spalling

causes the metal to come off in flakes.

When bearings overheat, many greases break down, leading to scoring and etching of

bearing surfaces. Water and corrosive elements can also create this condition, and

spalling often follows. A lubricant that is burned or oxidized can leave a dark coating on

bearing surfaces, while excessive pre-load with tapered roller bearings can have the same

effect. Excessively hot bearings can also cause deformed cages and seals, leading to

bearing lock-up.

Seals play an important role in extending bearing life. If contaminants get inside, they

can create wear patterns known as bruising. Because used seals can leak and contaminate

brake linings or cause bearing failure, it is important to avoid re-using them.

Quality differences among bearings also

have a direct effect on their longevity.

Bearings that use low-quality steel and

receive inferior heat treatment will wear and

spall more quickly than high-quality bearings.

Because even a small distortion in a seal can

lead to shortened bearing life, using a highquality

set of seal drivers is important when

installing serviceable bearings, while use of a

high-quality grease also effectively extends

bearing life. Unit hub assemblies, on the

other hand, are maintenance-free units that

are pre-set, pre-greased and pre-sealed. In

order to avoid damaging the axle nut threads

Worn-out bearings

can usually be

blamed on either

inadequate lubrication

or improper

installation or adjustment,

and it is important

to pinpoint the

reason for failure

before starting repair

procedures.

Bearings and shocking CV joints, OEMs and bearing manufacturers recommend

using a torque wrench for bearing installation.

A common practice that often leads to premature bearing failure

is overtightening of adjustable tapered roller bearings. These

bearings are never pre-loaded when located on the front of rear

wheel drive vehicles, and they’re snugged with no more than 15

to 20 ft. lbs. of torque while rotating the wheel to ensure the bearings

are seated. The adjustment nut is then loosened 1/6 to 1/4

turn and locked in place with a cotter pin.

Endplay should be around 0.001 to 0.005 inches. Although there

should be no play on most front wheel drive cars, up to 0.010 inch

of play in the front bearings of rear wheel drive vehicles may be

acceptable.

The bearing adjustment procedure for front wheel drive vehicles

with adjustable tapered roller rear wheel bearings is usually the

same as with rear wheel drive vehicles (zero pre-load), although

some models do require a slight pre-load.

Formulated with top-of-the-line synthetic oils, lithium complex

thickeners and premium additives, AMSOIL synthetic greases

offer unsurpassed protection and performance in extreme operating

conditions, protecting bearings against spalling, scoring and

wear.