Lesson 2/Learning Event 3
Learning Event 3:
Maintenance of airhydraulic brake systems is much the same as that
for straight hydraulic brake systems. The major difference between
the two is that the airhydraulic system contains components for
compressing air and applying air pressure to the hydraulic system.
As with any other automotive system, a wellorganized sequence of
events must take place to properly maintain airhydraulic braking
systems. The steps to take include a preroad test inspection, a road
test, and an afterroad test inspection to determine if there are any
troubles, a troubleshooting step to determine the cause of any
failure, and then the service and repair required to correct the
The maintenance procedures between 2 1/2 and 5ton military vehicle
braking systems will not vary too much. Therefore, throughout this
lesson, general maintenance practices will pertain to all air
BEFORE ROAD-TEST INSPECTION
Many times a good visual inspection is all that is needed to locate a
brake failure. However, to ensure that all parts of a braking system
are working properly, a complete inspection should be made.
The best place to start a visual inspection is at the brake pedal.
Check to ensure the pedal does not bind and that it operates the
linkage correctly. When the pedal is released, spring tension should
return it to its released stop position. Check to ensure there is
enough free travel in the pedal movement to allow the brakes to
completely release when the pedal is released. Check for wear on the
pedal bushing. The pedal should move freely but not have any
sideways motion. Check the pedal travel for sponginess which would
indicate air in the hydraulic system.
Inspect the master cylinder next. Check the fluid level and correct
it if necessary. Using the proper tools, check all the mounting
bolts to see if they are tight. Check the cylinder for leaks in the
housing, around the dust boot, and at all fittings where lines are
connected. Ensure the reservoir vent operates properly.