Lesson 1/Learning Event 3
Drive
The vehicle, when turned in either direction, tries to turn more rapidly
than the operator intends. This can be caused by bent, loose, or broken
parts. This is especially true if the steering gear assembly is loose on
the frame.
Wandering and drive can both be caused by loose steering parts, and several
malfunctions have the same symptoms. For example, hard steering and
wandering have the same symptomthe operator must "fight" the steering
wheel.
The good troubleshooter always makes a complete inspection of the components
before removing or replacing any parts.
STEERING GEAR INSPECTION
Description of steering gear (1/4-ton truck M151)
This steering gear assembly is the wormandroller type. The roller has two
teeth that mesh with the worm, so it is usually called a two or double
tooth roller. The steering gear is mounted on the body frame left side
rail. The steering column is supported by a bracket attached to the
instrument panel.
The steering gear worm gear is pressed on the steering shaft. Two tapered
roller bearings support and prevent endwise movement (thrust) of the worm
and shaft.
A steel trunnion pin attaches the double roller to the sector shaft. The
sector shift is mounted in bushingtype bearings pressed into the steering
gear housing. An adjustment screw engaged in the sector shaft is threaded
into the cover and controls sector shaft end play as well as the lash
(movement) between the teeth of the worm and the roller. Adjustment of the
worm thrust bearing is made by installing or removing gaskets of various
thicknesses between the gear housing and the housing cap.
A balltype bearing pressed into the steering column tube supports the shaft
at the steering wheel end.
The pitman arm and the steering wheel have fluted serrations (splines), with
one serration being double width. The doublewidth splines match blind
splines on the sector shaft and the steering shaft to ensure correct
installation.
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