ARB RD131 - Manual (Page 16)

4 Installing the Air Locker
14
4.5 Drilling and Tapping the Bulkhead Port
An air line port must be drilled and tapped through the differential
housing to mount the bulkhead fitting into.
Mark a spot on the exterior of the differential cover plate in the
position shown in Figure 6. (i.e., toward the bottom in the center of
the flat area that will be accessible from the outside and clear of all
moving components inside).
Figure 6.
Secure the differential cover plate to a work bench.
Drill an 11.2mm [7/16”] diameter hole through the differential
housing square to the outside surface.
Tap the hole from the outside using ¼”NPT thread tap.
Remove any sharp edges that may chip off from around the hole
and fall into the housing.
Thoroughly clean the cover plate to remove any filings from drilling.