AIR BRAKES-GENERAL INFORMATION
Initial Test Speed - If other than the recom-
mended 64 kmh (40 mph). If speeds of 64
kmh are not permitted in the area chosen
for the test, the test speed for the snubs
can be reduced to 30 mph. Whatever
speed is used, it should be the same for
each of the checks noted below.
Check the brake torque output of the tractor and
trailer in combination and individually as follows:
NOTE - An observer should be used to record all data for
these tatas. Only the SUSTAINED decelerometer
reading a should be recorded and not the peak readings
at the beginning and end of each step.
Tractor-Traller Combination Torque Output
determine whether the combination
combination in a suitable test area, make
three (3) stops from 64 kmh (40 mph) at
deceleration reading (to the nearest .5
ft./sec.2) for each stop in the appropriate
space on the Data Sheet. Determine the
average for the three readings.
Tractor Torque Output
With the service brakes released, close the
shut-off cock in the double gladhand
connection between the tractor and trailer.
WARNING - SINCE CLOSING THE SHUT-
VEHICLE. IF POSSIBLE, USE A NON-
PUBLIC AREA FOR CONDUCTING THE
combination, this time using the tractor
brakes only to make three (3) stops from 64
kmh (40 mph) at 276 kPa (40 psi) brake
decelerometer readings on the Data Sheet;
determine and record the average reading.
Trailer Torque Output
With the service brakes released, open the
shut-off cock In the double gladhand
combination and, using only the trailer hand
control valve (Figure 34) make three stops
from 64 kmh (40 mph) at 276 kPa (40 psi)
and record the readings and average on the
NOTE - It may be helpful to preload the traller air
lines for smooth brake application and more
accurate test results. This Is accomplished by
maintaining vehicle speed while lightly applying
the hand control valve just prior to the test stop.
Figure 34 - Trailer Hand Control Valve
Add the average deceleration reading for the
tractor to the average deceleration reading for
The sum should be within +.5 ft./sec.2 of the average
deceleration reading obtained from the combination test.
If not, the individual tractor and trailer torque output tests
must be rerun.
Evaluating the Performance of Tractor and Trailer
From the test results, compute the Balance
Ratio using the following formula:
NOTE - Typical Weights In the formula are those
weights normally being carried by the vehicle. If
a realistic estimate cannot be made, it Is
recommended that the tractor and trailer (with
typical load) be weighed.
Record the Balance Ratio on the Data Sheet. a If
the balance ratio is 1.00, the tractor-trailer
combination is in ideal torque balance.
CTS-4154Y - Page 33