FOOT THROTTLE VALVE
The foot throttle valve is a treadle operated air valve
mounted on the superstructure cab floor. The valve
controls the air pressure to the air cylinder mounted
characteristics or a low pressure warning
on the engine, which in turn controls the engine rpm.
may indicate a malfunction in one or the
other brake circuit, and although the
vehicle air brake system may continue to
function, the vehicle should not be
Chock the wheels.
operated until the necessary repairs
have been made and both braking
Deplete the pressure in both air systems.
circuits, including the pneumatic and
mechanical devices are operating
Disconnect the air lines from the foot throttle
normally. Always check the vehicle
brakes after performing brake work and
before returning the vehicle to service.
Lift the rubber material on the pedal and
remove the two screws, lockwashers, and nuts
Check the delivery pressure of both No. 1
securing the throttle bracket to the pedal. Leave the
and No. 2 circuits using a test gauge known to be
bracket connected to the cable.
accurate. Depress the treadle to several positions
between the fully released and fully applied
positions, and check the delivered pressure on the
securing the throttle valve and pedal assembly to the
test gauges to see that it varies equally and
cab floor. Remove throttle valve and pedal assembly
proportionately with the movement of the brake
from the hole in the cab floor.
After a full application is released, the reading
on the test gauges should fall off to zero promptly.
If installing a new pedal assembly, it will be
It should be noted that the No. 1 circuit delivery
necessary to drill two 0.281-inch (7.14 mm)
pressure will be about 2 psi (138 kPa) greater than
diameter holes in the upper end of the pedal using
the No. 2 circuit delivery pressure with both supply
the throttle bracket as a template. Lift the rubber
reservoirs at the same pressure. This is normal for
material from the pedal. Do not drill through the
Position the throttle valve and pedal
assembly through the hole in the cab floor and
Make and hold a high pressure (80 psi [5516
Coat the exhaust port and body of the brake
Lift the rubber material on the pedal, position
valve with a soap solution.
the throttle bracket on the pedal and secure it with
the two screws, lockwashers, and nuts.
Leakage of a 1 in. (2.54 cm) bubble in three
seconds is permitted.
Connect the air lines to the foot throttle valve.