Axle BearingsAxle bearings are what your vehicle rolls on. Whether your vehicle is front wheel
drive (fwd), rear wheel drive (rwd), or all wheel drive
(4wd), it has an axle bearing at each wheel. In this article we will explain what
they are and what they do, and what to look and listen for if you suspect you have
a bad axle bearing. All vehicles ride on axle bearings, there are different applications
depending on the vehicle, but the same principle applies. Rear wheel drive vehicles
use an axle that is mounted in the rear end housing and utilizes an axle bearing
at the outer (wheel) end to support the axle. Front wheel drive vehicles have an
outer axle bearing as well sometimes referred to as a “hub bearing”. Both axle bearings
do the same job; they are just a little different in appearance. Rear wheel drive
axle bearings are usually pressed into either the
rear end housing or are pressed
onto the axle itself whereas front wheel drive axle bearings are mounted in the
front spindle assembly. Fwd applications usually bolt into the spindle assembly,
but on older models they are pressed in and will require special tools and equipment
to replace them.Axle bearings can last over 100k miles depending on the application. A truck
used to carry heavy loads will most likely need them before a small fwd vehicle
that is used for commuting. When wheel bearings begin to go bad, you will usually
hear a slight grinding noise, this
noise will usually change when turning the vehicle as the load changes on the bearing
when the car transfers weight. In most instances if you turn the vehicle right and
the noise goes away or diminishes, you most likely have a bad right side axle hub
bearing, same theory goes for left turns. On rear wheel drive applications, a gear
oil leak is usually the first indicator
of a bad axle bearing. When the bearing begins to go bad, it will let the axle move
more than the axle seal can compensate for, causing a gear oil leak. This should
be repaired as soon as possible, if the leak is bad enough it can actually catch
fire from the heat generated by the
brakes. When replacing your axle bearings, always use a high quality OEM (Original
Equipment Manufacturer) replacement part. Less expensive bearings are that for a
reason, they usually use a lower grade of steel and can fail much sooner than an
OEM part.Bearings consist of an inner race, outer race and the bearings themselves that
are between the two races. The races are hardened steel pieces that isolate the
bearing from the piece it is pressed into (axle tube) or mounted onto (spindle).
Whether the inner or outer race is the stationary one will depend on the application.
All bearings are constructed of hardened steel.Axle bearings are made in much the same way, with some slight differences depending
on application. Severe duty applications will use a roller style of bearing, which
means it consists of several cylindrical hardened bearings riding between two races,
this style of bearing helps dissipate the load over a wider area. Vehicles that
don’t see severe duty usually use a ball style bearing, which is the same inner
and outer race, but with round bearings instead of cylindrical. Both of theses style
bearings are usually used in rwd applications and are lubricated by the rear end
oil. Most fwd applications use what is called a ”sealed” bearing assembly. These
bearings require no external lubrication and contain the seal as part of the bearing
assembly. On older rwd vehicles the front axle bearings, or “wheel bearings” as
they are commonly called consist of 2 separate bearings, inner and outer and a grease
seal. These are roller style bearings, usually cone shaped so that the axle nut
can set the preload (tension). Wheel bearings of this style require the proper high
temp bearing grease to keep them lubed, and will fail if not properly lubed.
Replacing axle bearings can be a difficult task for the do-it-yourselfer. On
fwd applications, you will need to separate the
lower ball joint from the control
arm, remove the axle from the outer hub assembly, and then bolt in the new one,
reverse procedure to assemble. If the bearing hub assembly doesn’t bolt in, you
may need to remove the entire spindle assembly and have it pressed apart and together
by an automotive machine shop. Rear wheel drive vehicles require the axle to be
removed from the rear end housing. On Some applications the axle is held in with
bolts at the end of the axle tube. After removing the brake caliper and rotor, the
axle should come out with the removal of these bolts. Other models will require
the differential cover to be removed to gain access to the cross pin and retaining
bolt. Once removed the axle can be pushed in a little allowing the “C” clip to be
removed, once the clip is removed the axle will pull out of the rear end housing.
Then the axle bearing can be removed with a slide hammer and the proper attachment.
The new bearing should be installed with the proper tool to keep it from being damaged.
Always replace the axle seals when doing the bearings and inspect the rear brakes
for oil contamination, if this has happened the
brake pads should be replaced at the same time to prevent any kind of stopping
problems. As with any vehicle repair, proper safety attire must be worn and the
vehicle needs to be properly supported before any work begins.
Written by Ken Lavacot Co-Founder and CEO of 2CarPros.com 35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.
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