Question:When I hit a bump, my car suddenly jerks to
one side. Is anything wrong?
Answer:Yes. The condition is called "bump steer,"
and it means your steering linkage is not mounted parallel in
the chassis possibly as a result of collision or frame damage,
a bent steering arm, misalignment in the chassis, or an improperly
mounted steering rack.
Bump steer is not a very common condition, but it can be a
very unnerving thing to experience if you're unfortunate enough
to encounter it. It is usually most noticeable when crossing
a major dip or bump at speed, as when crossing a railroad crossing
or passing through an intersection with a lot of road crown.
As the suspension bounces over the bump, it suddenly feels as
if someone tugged on the steering wheel. The car twitches or
jerks to one side as if it has a mind of its own. This occurs
because of unequal toe changes that occur as the suspension extends
and compresses.
In a properly aligned car, the toe alignment of both front
wheels changes equally as the suspension moves up and down. But
if something causes more of a toe change in one wheel than the
other, it will jerk the steering towards the side with the greatest
toe change.
The thing that needs to be checked is the parallelism of the
steering rack and linkage with respect to the ground. This can
be done by simply measuring the distance between both ends of
the rack and the ground. If one end of the rack is sitting higher
than the other, the rack is misaligned in the chassis. If it
can't be corrected by loosening and retightening the rack mounts,
the subframe or crossmember on which the rack is mounted may be
bent or damaged. This will require special straightening equipment
or replacement to correct.
The height of the outer ends of the tie rods with respect
to the ground should also be measured. If one tie rod is higher
than the other, one of the steering arms is probably bent. The
cure here is to replace the steering knuckle.
CAUTION: Bending a steering arm to "correct" a
bump steer condition is not recommended because doing so may weaken
the arm and increase the danger of it breaking.
