BRAKE SYSTEM CONTINUED
Air Control System
The modulator air system consists of a pressure regulator which receives system air pressure from a bottom port
on the right treadle valve and reduces the system pressure from 105 to 70 psi (723.9 to 482.6 kPa), an air solenoid
valve which controls air flow from the pressure regulator, and a double check valve which channels air flow to the
double check valve on the right treadle (for brake application) and to the neutral knockdown valve (for transmission
disconnect). A third air line between the double check valve and a top port on the left treadle allows (upon full
application of either left or right treadle) full system air pressure 105 psi (723.9 kPa) to override the modulator
application 70 psi (482.6 kPa) of the brakes and neutral knockdown valve.
Pressure Regulator Check and Adjustment. The pressure regulator has an air pressure gauge in the body of
the regulator. The gauge should not read over 70 psi (482.6 kPa). If the pressure indicated is not below 70 psi
(482.6 kPa), loosen the locknut and turn the adjusting screw. Apply a brake treadle several times till the air
pressure is below 70 psi (482.6 kPa). Then back off the adjusting screw until compression is released from
pressure spring. Re-adjust pressure by turning adjusting screw clockwise until the 70 psi (482.6 kPa) pressure is
reached. Tighten the locknut.