WORM BEARING PRELOADAssures that
the worm shaft is held snugly inside the gearbox
housing. If the worm shaft bearings are too loose, the
worm shaft can move sideways and up and down during
OVER CENTER CLEARANCEControls the
amount of play between the pitman arm shaft gear
(sector) and the teeth on the ball nut. It is the most
critical adjustment affecting steering wheel play.
Set the worm bearing preload first and
then the over center clearance.
The basic procedures for adjusting worm-bearing
preload are as follows:
Disconnect the pitman arm from the pitman arm
shaft. Loosen the pitman arm shaft overcenter adjusting
locknut and screw out the adjusting screw a couple of
turns. Then turn the steering wheel from side to side
Using a torque wrench or spring scale. measure
the amount of force required to turn the steering wheel
to the CENTER position. Note the reading on the torque
wrench or the spring scale and compare it to the
If readings are out of specifications. loosen the
worm-bearing locknut. Then tighten the worm bearing
adjustment nut to increase the preload. Loosen it to
decrease preload and turning effort. With the preload set
to specifications. tighten the locknut. Make sure the
steering wheel turns freely from stop to stop.
If the steering wheel binds or feels rough,
then the gearbox has damaged components
and should be rebuilt or replaced.
The basic procedures for adjusting the over center
clearance are as follows:
Find the CENTER position of the steering wheel.
This is done by turning the steering wheel from full right
to full left while counting the number of turns. Divide
the number of turns by two to find the middle. This
allows you to turn the steering wheel from full stop to
Most gearboxes are designed to have more
geartooth backlash (clearance) when turned to
the right or left. A slight preload is produced in
the center position to avoid steering wheel
play during straight-ahead driving.
With the steering wheel centered, loosen the over
center adjusting screw locknut. Turn the over center
adjusting screw in until it bottoms lightly. This will
remove the backlash.
Using the instructions in the service manual,
measure the amount of force required to turn the
steering wheel. Loosen or tighten the adjustment screw
to meet the manufacturers specifications. Tighten the
locknut and recheck the gearbox action.
When adjustment fails to correct the problems, the
steering gearbox needs to be overhauled or replaced.
Overhauling a gearbox is done by disassembling,
cleaning, inspecting, replacing worn components, and
seals. After reassembling the gearbox. fill the housing
with the correct type of lubricant. Most manual
steering systems use SAE 90 gear oil. Make sure that
you do NOT overfill the gearbox. Refer to the
manufacturer's service manual for the particular
gearbox you are working on since procedures,
specifications, and type of lubricants vary.
and-pinion steering systems have few parts that fail.
When problems do develop, they are frequently in the
tie-rod ends. When NOT properly lubricated, the rack
and pinion will also wear, causing problems.
Depending upon the manufacturer, some
rack-and-pinion steering systems need periodic
lubrication. Others only need lubrication when the unit
is being reassembled after being repaired.
Most rack-and-pinion systems have a rack guide
adjustment screw. This screw is adjusted when there is
excessive play in the steering. Basic procedure for
adjusting rack-and-pinion steering system is as
Loosen the locknut on the adjusting screw. Then
turn the rack guide screw until it bottoms slightly. Back
off the rack guide screw the recommended amount
(approximately 45 degrees or until the prescribed
turning effort is achieved).
Tighten the locknut. Check for tight or loose
steering and measure steering effort. Compare with the
manufacturer's specifications. If not with