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To increase gear lash, use a thicker
shim. Gear lash can also be adjusted
by changing the driven pinion bearing
housing shim(s) in the same way.
Too little gear lash is extremely des-
tructive to gears. Always recheck an
assembled component for specified
D. Tooth Pattern Inspection and Adjustment
(1) The middle gear case must be relatively
free of oil, with only enough to protect
the bearings. Clean the gear teeth
with spray solvent.
(2) To mark the gears, use a white paint.
White lead or artist's oil zinc white
may be used. The paint must be
smooth and firm, with the consistency
of toothpaste. Apply this paint to 3 or
4 driven pinion teeth. Cover the
contact faces of the teeth.
(3) Use the middle gear holding tool to
turn the pinion shaft while holding
the driven pinion flange to simulate a
load. Turn for 2 or 3 revolutions.
Then reverse the rotation and load
for 2 or 3 revolutions.
(4) Remove the bearing housing cap and
tap out the drive pinion shaft. Inspect
the gear tooth patterns.
Example 1. Correct pattern
NOTE:
The pattern should be centered in the
tooth drive surface. However, wear
and drive forces tend to move the
contact area to the out side. Therefore
the correct pattern can be slightly
toward the inside, or heel, of the gear
tooth.
(5) To correct an incorrect tooth pattern,
change the total shim thickness at
each location (A and B) an equal
amount. The shims must be changed
an equal amount or gear lash will be
affected. Use the following guide:
Example 2. Incorrect pattern
Decrease shim thickness at A increase
shim thickness at B an equal amount.
Example 3. Incorrect pattern
Increase shim thickness at A decrease
shim thickness at B an equal amount.
Remove original contact pattern and
recheck with fresh paint. If the new
pattern is correct, thoroughly clean all
paint from the teeth and flush the
case several times with solvent to
remove all traces of paint. Immediately
oil all bearings with gear oil. Recheck
gear lash.
Driven
pinion
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