Question:My mechanic says my car needs ball joints.
Please explain.
Answer:Ball joints are a part of your vehicle's suspension
that connects the steering knuckles to the control arms. A ball
joint is essentially a flexible ball and socket that allows the
suspension to move and at the same time the wheels to steer.
Cars and trucks without strut suspensions typically have four
of them (one upper and one lower on each side). Cars and minivans
with strut suspensions have only two (one lower ball joint on
each side). Some front-wheel drive cars also have ball joints
on the rear suspension.
Like any other suspension component, ball joints eventually
wear and become loose. Excessive play in the joint can affect
wheel alignment and tire wear. Loose joints can also cause suspension
noise (typically a "clunking" sound when hitting a bump).
WARNING: If a ball joint fails, the suspension can collapse
causing a loss of control. So don't put off having a bad set
of joints replaced.
JOINT INSPECTION
Joints should be inspected before they're greased (since grease
takes up some of the slack in the joint). Ball joints are pretty
easy to check, but each type requires a different inspection procedure.
Use the wrong procedure and you'll get misleading results. The
procedure that needs to be used depends on the location and loading
of the joint:
* LOWER LOAD CARRYING ball joints are found on front- and
rear-wheel drive vehicles where the coil spring or torsion bar
is on the lower control arm. You'll also find them on the rear
suspension of 1985 & up FWD Buick, Cadillac, Pontiac &
Oldsmobiles, too.
Joints with built-in wear indicators (most GM and Ford RWD
cars, rear joints on the FWD GM cars, and GM RWD vans, S10 &
S15 Blazer) must be checked with the full weight of the vehicle
on the tires on the shop floor or on a drive-on style ramp --
not with the wheels up or the suspension supported by jack stands.
No measurements are required if a joint has a wear indicator
because internal play is indicated by the position of the grease
fitting boss. The boss protrudes about .050 inches on a new joint.
As the joint wears, the boss recedes into the housing. The joint
is considered "good" as long as you can see or feel
the edge of the boss protruding from the housing. But if the
top of the boss is flush or below the housing, it's time to replace
the joint.
On lower load carrying ball joints without a wear indicator,
the joint is checked in the unloaded condition with the wheel
raised off the ground and the lower control arm supported by a
jack stand. A dial indicator is then used to measure play in
one of two directions: sideways (horizontal or radial play) or
vertically (axial or up-and-down play). The direction to measure
depends on the application (refer to a manual for the exact specs).
Sideways play is measured with the indicator positioned against
the inside of the wheel rim near the joint. The wheel should
be pushed in and out by hand to check sideways play, and lifted
with no more than 25 lbs. of force to check vertical play. Many
joints allow up to .250 in. of sideways (radial) play, but some
allow no play or only .015 in. of play. Always refer to the vehicle
manufacturer's specs.
Vertical play is measured with the dial indicator positioned
against the knuckle stud nut (Ford & GM) or the joint housing
(Chrysler). A joint that has more than .050 in. of vertical play
doesn't necessary require replacement because the specs range
from zero play to as much as .125 inch of play.
The most common mistake that's made here is to use too much
pressure on a pry bar or to insert a pry bar between the control
arm and knuckle rather than under the wheel. Pry hard enough
and any joint may appear to be bad.
* LOWER FOLLOWER NONLOADED ball joints are found on two kinds
of applications: RWD cars where the spring is over the upper control
arm, and vehicles with MacPherson strut suspensions. On both
applications the lower joint is checked with the wheel raised
off the ground hanging free (no stand under the lower control
arm). Rock the wheel in and out by hand. A good joint should
show no movement.
One exception here is 1978-80 Omni & Horizon which allows
up to .050 inch of sideways play. Another exception is Chrysler
FWD minivans and FWD cars ('81 & up). On these applications,
the lower joint has a wear indicator grease fitting. Joint play
is checked with the wheels on the ground rather than raised.
If the grease fitting can be twisted with your fingers, the joint
needs to be replaced.
* UPPER LOAD CARRYING ball joints are found on vehicles where
the spring or torsion bar is on the upper control arm. Like the
lower follower nonloaded ball joints, the upper joints are checked
in the unloaded condition with the wheels off the ground -- but
with a wedge or block between the frame and upper control arm
to support the upper arm. On most applications, any movement
calls for replacement. But on some Fords, up to .250 in. of radial
play is allowed.
* UPPER FOLLOWER NONLOADED ball joints are also checked with
the wheels off the ground but with the lower control arm supported.
Any movement usually calls for replacement.
JOINT REPLACEMENT
Any joint that exceeds the vehicle manufacturer's maximum
allowable wear needs to be replaced. The greater the amount of
wear, the greater the urgency to replace it.
Ball joints are often replaced in complete sets, or at least
in matched pairs on both sides (both lowers or both uppers).
This is because the joints on both sides of a vehicle usually
have the same amount of wear. If one is bad, the other usually
is too. Load carrying ball joints usually wear out before ones
that don't carry a load, so it may only be necessary to replace
the loaded joints instead of the complete set.
Replacing a set of ball joints requires separating the control
arms from the steering knuckles, a job which can be difficult
depending on the design and age of the vehicle. At the very least,
it usually requires a special "ball joint fork" tool
to loosen the ball joint stud from the knuckle. If this sounds
like more of a a job than you want to tackle, let a professional
do it the work.
