Why should ball joints and tie rod ends be changed in pairs?
It is not absolutely necessary, but many professional installers
insist on replacing both even if only one is bad. This is because
both have more or less the same mileage and sooner or later the
other one is going to fail too.
In many instances, the companion part on the opposite side is
marginal, so it makes sense to replace both ball joints (uppers
and/or lowers) or both tie rod ends (inner and/or outer) at the same
time. It also saves the customer the inconvenience of having to
bring his vehicle in a second time.
There is some evidence to suggest that suspension and steering
components on the right side of a vehicle have a somewhat higher
rate of failure than those on the left side. The right side takes
more punishment when it comes to close encounters with curbs,
potholes and other obstacles, and the typical vehicle makes more
righthand turns than lefthand turns.
Even though all suspension components have the same mileage, those
on the right side often need to be replaced at a lower mileage than
those on the left.
It is important to check tie rod ends when doing any type of
suspension work.
Some components also wear faster than others. Loaded ball joints
(those that bear the brunt of the vehicle's weight) wear out faster
than unloaded ball joints. Loaded ball joints are the lower ones on
vehicles where the spring rests on the lower control arm, and the
upper joints on vehicles where the spring rests atop the upper
control arm. The lower ball joints on FWD cars are unloaded.
Outer tie rod ends also tend to wear out faster than inner tie rod
ends because the outer ones experience more deflection and are more
exposed to road splash, salt and dirt. Inner tie rod sockets on
vehicles with rack and pinion steering are protected by bellows, so
the rate of replacement for the inner sockets is only a fraction of
that for the outer tie rod ends.
The real issue here is not which parts wear out first or why, but
how your customer's needs can be best served. If only one tie rod
end or ball joint is obviously shot, but its partner on the opposite
side still appears to be in good condition (and the customer cannot
afford to replace both at the same time) then do not tell him he has
to change both.
Better to sell only what he needs now and get his repeat business
when the other part fails than to risk losing his business by trying
to sell him parts he is not convinced he really needs.
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