Figure 6-14.Automotive type emergency/parking brake axle mounted.
are usually mounted on the output shaft of the
transmission or transfer case directly in the drive line.
Theoretically, this type of system is preferred for heavy
equipment because the braking force is multiplied
through the drive line by the final drive ratio and the
braking action is equalized perfectly through the
differential. Drawbacks are that severe strain is placed
on the power transmission system, and also that the
vehicle may move while it is being lifted since the
differential is not locked out.
Parking brakes interconnected with service brakes
are usually found on automotive types of equipment
(fig. 6-14). This type of emergency/parking brake is
actuated by a foot pedal or a dash mounted handle
assembly and is connected through linkage to an
equalizer lever (fig. 6-15), rod assembly, and cables
connected to the emergency/parking brake mechanism
within the drums/discs (fig. 6-14) at the rear wheels.
When you test parking brakes, stop the vehicle on a
road graded at about 30 percent. Set the parking brake
and release the service brakes. The vehicle should
maintain its position and not roll or inch backwards.
Repeat the test in the opposite direction. Again, the
vehicle should hold its position. If there is no hill close
by, you may test parking brakes by setting the brake,
placing the vehicle in first gear (low), and slowly
releasing the clutch with the engine idling (do not rev
the engine while doing this exercise). This action should
stall the engine of the vehicle you are testing. In the case
of an automatic transmission, the vehicle should not
move in any gear. In either of these tests, if the vehicle
does move, it is an indication that there is a parking brake
Once you determine there is a problem, proceed as
follows. First, inspect the condition of the emergency
brake linings and contact surfaces just as you would for
service brakes and just as carefully. Pay attention to the
ratchet and paw] or any other automatic locking device
that holds the brake in the applied position to make sure
it is operating properly. In addition, when inspecting the
drive line type brake, examine the universal joints and
splines for loose bolts and grease leaks. Loose bolts are
not uncommon for vehicles having brakes mounted in
the drive line.
The emergency brake must hold the vehicle on any
grade. This requirement covers both passenger and
commercial motor vehicles equipped with either the
enclosed type of emergency brake at each rear wheel or
a single emergency brake mounted on the drive line. The
Figure 6-15.Equalizer linkage.