1935 Cadillac - GM Heritage Center

32
REAR
AXLE
of the pinion gear teeth. Such markings as L-43,
L-5-7, etc., will be found. The numeral following
the letter "L" such as 4 or 5 indicates the recommended
backlash in thousandths of an inch.
When checking the backlash the axle shafts
should be pulled out of the differential side gears
and the drive pinion held stationary. The amount
of backlash can be meausred by means of a dial
indicator with holder, tool No. HM-91220, clamped
to the axle housing and in contact with a tooth on
the ring gear as shown in Fig. 17. If the backlash
is within these limits the gears can be checked for
proper meshing.
Correct meshing of the ring gear and drive
pinion can best be determined by painting the
working surface of the ring gear teeth with red
lead mixed with gasoline as a thinner, or Prussian
blue, as explained under "Testing Ring Gear for
Proper Tooth Contact."
After the correct position for the ring gear is
found, the adjustment of the bearings should be
checked. The bearing caps are then tightened
and the locking plates and differential cover are
installed, after which the differential should be
properly lubricated.
Testing Ring Gear for Proper Tooth Contact
Correct meshing of the gears can best be determined
by first painting the working surfaces of the
ring gear teeth with red lead thinned with gasoline,
or Prussian blue, and turning the ring gear several
revolutions by hand and then noting the tooth
contact obtained on the ring gear under load.
When the gears are turned the red lead or Prussian
blue is wiped off at the point where the teeth of
the ring gear and pinion mesh.
It is important to make this test by hand first
so that an initial adjustment can be made if the
gears are not correctly meshed. The tooth form
may easily be ruined by running the gears under
load when not correctly meshed.
To test the gear mesh under load the rear wheels
should be raised off the floor and driven in both
directions with the engine. The necessary load
can be obtained by applying the brakes. Care
should be taken in making this test not to run the
ring gear more than ten or twelve revolutions at a
time before checking the tooth contact. If the
bearings and gears are in proper adjustment, the
lengthwise tooth contact on the ring gear, which
is the contact along the length of the tooth, and
the profile tooth contact on the ring gear, which is
the contact from top to bottom of the tooth, will
appear as shown in Fig. 12, Plate 7 (a) for the forward
speeds and as shown in (b) for the reverse
speed.
It will be noted that the tooth contact for the
forward speeds under light load is at the small end
or "toe" of the tooth. This is necessary due to
spring in the housing and the bearings under
driving loads in the forward speeds, under which
condition the tooth contact will shift toward the
large end or "heel" of the tooth. Under no conditions
should the tooth contact on the ring gear
under light load be at the heel of the tooth, as a
heavy load on the gears m any of the forward
speeds would tend to concentrate the load at this
point.
In reverse, the tooth contact does not shift as far
toward the heel under load as the driving contact.
It is, therefore, permissible to have the contact
on the reverse side more nearly at the center of the
tooth than is the case on the driving side.
The profile contact, or the contact from top to
bottom, on the face and flank of the tooth, may
appear at any position throughout the length of
the tooth. For proper meshing of gears the greater
part of the profile contact on the ring gear should
be about the middle of the tooth at the pitch line
slightly below the outer edge. Referring to Fig. 12,
it will be noted that the contact surface for the
ideal condition extends only slightly below the
pitch line and almost to the edge of the tooth. If
the contact surface favors a lower position on the
flank of the ring gear tooth, as shown in Fig. 13, the
profile contact is too low. If, on the other hand,
the contact surface is totally above the pitch line
and also shows a decided contact on the top
point or face of the tooth, the profile contact is too
high.
To correct a low profile or flank contact, move
the drive pinion away from the ring gear. This
adjustment will increase the backlash and it may
be necessary to move the ring gear toward the
drive pinion to keep the backlash within the
limits. Changing the position of the ring gear will
alter the lengthwise contact on the tooth and to
obtain correct tooth contact, illustrated in Fig. 12
(a) and (b), several adjustments for lengthwise
and profile contact, may be required.
To correct a high profile or face contact, move
the drive pinion toward the ring gear. This will
decrease the backlash and it may be necessary to
move the ring gear away from the pinion to maintain
the proper amount of backlash. Changing
the position of the ring gear will change the lengthwise
contact on the tooth and to obtain a correct
tooth contact, illustrated in Fig. 12 (a) and (b)
several adjustments for lengthwise and profile
contact may be required. After obtaining the
proper tooth contact under load, check the backlash
to see if it is within the limits.
When the "toe" contact on both the driving
and reverse sides of the tooth is extended too close
to the end of the tooth as shown in Fig. 14 (a) and
(b) respectively, increase the backlash between
the gears, keeping it under .012 in. by moving the
ring gear away from the drive pinion. This may