B
MECHANICAL BRAKES
Read all of SAFETY and this section before attempting any procedure. Pay particular attention to Notices, Cautions, Warnings and Dangers.
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Repair and Service Manual
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Periodic Brake Performance Test (PBPT)
To prevent a severe injury or death
resulting from operating a vehicle
with an improperly operating brake
system, the braking system must be properly
maintained. All driving brake tests must be done in a
safe location with regard for the safety of all
personnel.
The Periodic Brake Performance Test (PBPT) should be
performed regularly as an evaluation of braking system
performance. It is useful as a method of identifying sub-
tle loss of performance over time and as part of fault
testing a problem vehicle.
Before performing this test, inspect the brake pedal and
linkage and correct any problems found including adjust-
ing the brake pedal free travel if required (See Brake
Pedal and Linkage Inspection on page 94).
The purpose of this test is to compare the braking per-
formance of the vehicle to the braking performance of
new or “known to be good” vehicles or to an established
acceptable stopping distance (Ref Fig. 12).
Actual stopping distances will be influenced by weather
conditions, terrain, road surface condition, actual vehicle
weight (accessories installed), and vehicle speed. No
specific braking distance can be reliably specified. The
test is conducted by latching the parking brake to elimi-
nate different pedal pressures and to include the affects
of linkage mis-adjustment. Significant changes or differ-
ences in braking performance will be evident due to mis-
adjustment.
Establish the acceptable stopping distance by testing a
new or “known to be good” vehicle and recording the
stopping location or stopping distance. For fleets of vehi-
cles, several vehicles should be tested when they are
new and the range of stopping locations or distances
recorded.
Fig. 12 Periodic Brake Performance Test
NOTICE: Over time, a subtle loss of performance
may take place; therefore, it is important to estab-
lish the standard with a new vehicle.
1.
Drive the vehicle at maximum speed on a flat, dry,
clean, paved surface (Ref Fig. 12).
2.
Quickly press the brake pedal to latch the parking
brake at the line or marker in the test area and
remove your foot from the pedal. The vehicle should
stop aggressively. The wheel brakes may or may not
lock.
Latch
Parking Brake
and Take Foot
Off Pedal
Line or Marker
Acceptable
Stopping
Distance
Normal Range of
Stopping Distance
Any vehicles that stop
more than 4 ft. (1.2 m)
beyond the Acceptable
Stopping Distance or
pulls to one side should
be removed from service
and inspected by a
qualified mechanic
Accelerate To
Maximum Speed
4 ft. (1.2 m)
Line or Marker
PRELIMINARY
