The rear end invariably is the last component of the automobile to
receive an upgrade or model change. But recently we have seen changes,
and many for the good.
“Generic gears”, sometimes referred to as “Hog Cut”, are a new
generation of crown and pinion gear. In these crown and pinion sets,
the gear tooth angle is changed and curved more in shape, giving the
gears a larger contact area for a given crown gear diameter. The
generic gears started showing up in GM cars in 1993 and are now used
almost industry wide. Difficulty can be experienced setting up these
gears for quiet operation. Excessive backlash is usually required to
achieve a good gear contact pattern.
Spider gears are changing also. Many makers are adding a tooth and size
to the spider gear and reducing the size of the side gear, consequently
evening up the gears' wear rate. The tooth angle has a more generic
cut, too. Some makers' spider and side gears appear to be pressed or
stamped out, instead of being machined. These gears, seen in Chrysler
and Mazda products, appear crude in manufacture, but the advantage is a
flange formed around the outer end of the tooth adding strength and
integrity to the gears.
With the demand for ABS, we must monitor the speed of the rear wheels.
Most makers install a tone ring to the crown gear flange or to the
pinion shaft with a sensor on the banjo housing or in the cover plate.
Toyota sometimes uses the crown gear teeth themselves as a tone ring.
Quite resourceful, but lacking some flexibility. These methods only
record both or one wheel locking, so the good guys install a tone ring
on each axle shaft with its own left or right sensor to record wheel
lock-ups individually.
Traditionally, almost all 4x4 front differentials were a rear unit
turned through 180 degrees and driven in reverse. This practice, though
economical, had major disadvantages, specifically poor ground clearance
and poor gear life as they were not designed to be loaded constantly in
reverse.
The oil flow was also disrupted, and the remedy was to raise the filler
plug location, thereby increasing the oil capacity. Now, almost all
front drives are a reverse spiral design (high pinion) where the pinion
enters the differential above the center line of the front axles. The
reverse spiral pinion turns anti-clockwise, applying pressure on the
large pinion bearing instead of pulling on the small bearing as on the
previous design.
Independent front suspension and shift on the fly are just about
standard on all 4x4 fronts. One ton and up vehicles have retained a
solid axle front, as high performance, car-like ride is not of primary
concern.
GM has an oil change schedule which requires under warranty that the
rear end oil be changed at 5,000 km and every 30,000 km, thereafter,
whether or not it has a posi-trac. It’s popular knowledge that GM
gov-nr-lok units are sensitive to aged oil, but this measure seems
extreme for a regular differential.
Posi-tracs of many styles are finding their way into the majority of
rear wheel vehicles these days. This helps traction immensely and
enhances braking efficiency.
If you have any questions or suggestions, please don’t hesitate to call us.
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