ARB RD109 - Manual (Page 24)

3 Installing the Air Locker
22
3.9 Checking the Backlash
Set a depth indicator on one of the ring gear teeth as in
Figure 14.
While supporting the pinion gear by holding the drive shaft, rotate
the differential in both directions while observing the maximum
variation in depth from the indicator (i.e., the highest value minus
the lowest value). This value is referred to as the ring and pinion
backlash.
Rotate the differential center 90
° and measure again for accuracy.
Figure 14.
Refer to your vehicle service manual for the specified maximum
and minimum amounts of backlash. If the backlash is not within the
specifications then the differential will have to be removed and re-
shimmed.