33–06 Steer Axle Hub Cap Vent
Plug Inspection
General Information
As a function of their design, hubcap vent plugs will
on occasion exhibit signs of hub oil on their exterior
surface. Depending on environmental conditions
and/or age of the plug, the amount of oil present can
vary. This is a normal result of the venting process
due to pressure increase within the hub cavity. For
an example of normal vent plug appearance, see
Fig. 13.
A vent plug can wear or be damaged and cause ex-
cessive leakage, or allow water to enter the hub and
contaminate the oil. For examples of a leaking vent
plug, see
Fig. 14 and Fig. 15. Evidence of a leaking
vent plug may appear as;
• Oil splatter around the wheel
• Gooey/gummy oil around the vent plug purge
point
• Hub/plug area is dirty, and water contaminated
oil in the hub.
• Hub/plug area is clean, but there is water con-
taminated oil in the hub. (pressure washing is
the most likely cause)
Inspection
NOTICE
Only remove vent plugs by hand. They can be
damaged if a tool is used. Wipe the hub/plug area
f33029809/01/2016
Fig. 13, Normal Oil Venting
f33029909/01/2016
Fig. 14, Excessive Leakage
f33030009/01/2016
Fig. 15, Water in Oil
Front Axle 33
108SD and 114SD Maintenance Manual, May 2017 33/7
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