Thwaites SPRITE NIMBUS, Manual

Page: 42 / 54

BACKLASH - CORRECTION PROCEDURE FOR ADJUSTMENT:
Remount the dial indicator on the gear carrier housing with the button against one
of the drive gear teeth, as nearly in line with the direction of tooth travel as possible,
see figure. Move the drive gear to check the backlash which should be as etched on
the gear. If the backlash is not in accordance with the specification, transfer the
necessary shims from one side of the differential case to the other to obtain the
desired setting. To increase backlash, remove shims from the drive gear side and
install on the opposite side. Backlash is decreased by transferring shims to the drive
gear side from the opposite side of the differential case.
After setting the backlash to the required figure, use a small brush to paint eight or
ten of the drive gear teeth with a stiff mixture of marking raddle, used sparingly, or
engineer’s blue may be used if preferred. Move the painted gear teeth into mesh
with the pinion until a good impression of the tooth contact is obtained. The
resulting impression should be similar to figure A in Table 7. Refer to the section on
Tooth Contact and to Table 7 for instructions on correction of tooth contact if the
impression obtained is not satisfactory.
Diff. Preload Shim Alice. 007" on All Models
Backlash ... ... ... As etched on Drive Gear (Minimum .004")
E Heel Contact Figure E shows an example of heel contact which is indicated by
the concentration of the bearing at the large end of the tooth. To rectify this
condition, move the drive gear closer into mesh, i.e. reduce backlash, by adding
shims to the drive gear side of the differential and removing an equal thickness of
shims from the opposite side.
NOTE: it is most important to remember when making this adjustment to correct a
heel bearing, that sufficient backlash for satisfactory operation must be maintained.
If there is insufficient backlash the gears will at least be noisy and have a greatly
reduced life, whilst scoring of the tooth profile and breakage may result. Therefore,
always maintain a minimum backlash requirement of .004".
BACKLASH:
When adjusting backlash always move the drive gear as adjustment of
this member has more direct influence on backlash, it being necessary to move the
pinion considerably to alter the backlash a small amount. (.005 “movement on
pinion will generally alter backlash .001").
GEAR & PINION MOVEMENT: Moving the gear out of mesh moves the tooth
contact towards the heel and raises it slightly towards the top of the tooth.
Moving the pinion out of mesh raises the tooth contact on the face of the tooth and
slightly towards the heel on drive, and toe on coast.
3-3-1