Operation and maintenance manual

Section 190-0270
SM 2252 10-03
3
Braking System
Stop Light Pressure Switch (2) - The normally open
(NO) pressure switch is located at a tee in 'B2' port of the
treadle valve. As brake apply pressure increases to
2.7 bar (39 lbf/in
2
) and above, the circuit closes and sends
a signal to illuminate the brake lights at the rear of the
vehicle. As pressure drops below 2.7 bar (39 lbf/in
2
) the
circuit opens and brake lights go out.
Rear Brake Pressure Switch (3) - The normally
closed (NC) pressure switch, located below the rear
brake accumulator, senses pressure in the rear brake
circuit. The pressure switch sends a signal to
illuminate 'Red' trailer brakes overstroke warning light
(7, Fig. 2) when pressure drops below 115 bar
(1 668 lbf/in²). An audible buzzer also sounds.
Front Brake Pressure Switch (4) - The normally
closed (NC) pressure switch, located below the front
brake accumulator, senses pressure in the front brake
circuit. The pressure switch sends a signal to
illuminate 'Red' tractor brakes overstroke warning light
(3, Fig. 2) when pressure drops below 115 bar
(1 668 lbf/in²). An audible buzzer also sounds.
Parking Brake Pressure Switch (5) - The normally
closed (NC) pressure switch, located in the brake
manifold valve, senses pressure in the parking brake
(Pk) line. The pressure switch opens at a pressure of
4.9 bar (71 lbf/in²) and sends a signal to illuminate
'Green' parking brake indicator light (8, Fig. 2) when
the parking brake is applied.
Brake Cooling Oil Temperature Switch (11) - The
normally open (NO) switch, located at the manifold
block on the front axle, senses oil temperature in the
brake cooling lines. The switch sends a signal to the
two speed control valve to increase brake cooler fan
speed when oil temperature reaches 50 °C.
Brake Cooling Oil Temperature Switch (12) - The
normally open (NO) switch, located at the manifold
block on the front axle, senses oil temperature in the
brake cooling lines. The switch sends a signal to
illuminate 'Red' brake cooling oil temperature warning
light (16, Fig. 2) when oil temperature reaches 120 °C.
Steering
Emergency Steering Pressure Switch (8) - The
normally closed (NC) pressure switch is located in a
block at the rear outlet port of the main hydraulic
pump. The pressure switch sends a signal to
illuminate 'Red' emergency steering warning light
(km/h) and miles per hour (mph). A digital odometer is
incorporated in the speedometer to record the
distance travelled by the vehicle at any given time.
Speedometer Calibration
1. Determine the impulse setting required. Reference
speedometer calibration table.
Electrical System - Switches and Sensors
2. Depress and hold calibration button at the front of
the speedometer and turn the ignition keyswitch to
position '1'. Release button when PULSE is displayed.
3. After a few seconds, the digits will flash in
sequence. Depress the button until the desired
number is displayed the release the button for a few
seconds until the next digit flashes.
4. Repeat step 3 to obtain the desired impulses/
revolution. The speedometer is now calibrated.
Retarder Proximity Switch (13) - Incorporated in the
treadle valve. The first 7° of pedal travel will request
the transmission retarder. The retarder will engage,
provided that the transmission 'Stop' warning light (12,
Fig. 2) is out and the transmission is in lockup. Further
depression of pedal will apply the service brakes. To
disengage the retarder, release the treadle valve.
Retarder Pressure Switch (14) - The normally open
(NO) pressure switch, located on top of the
transmission, senses pressure in the transmission
retarder line. As retarder pressure increases to
0.3 bar (4.4 lbf/in
2
) and above, the circuit closes and
sends a signal to illuminate the retarder apply indicator
light (15, Fig. 2).
Oil Temperature Sender (6) - Sends a signal to
indicate transmission oil temperature on the
transmission oil temperature gauge (20, Fig. 2) in the
cab.
Kickdown Switch (7) - Refer to Section 120-0010,
TRANSMISSION AND MOUNTING, for detailed
operation of the kickdown switch.
Speedometer Calibration Table -
All units with standard tyres
Unit Transmission Pulses
TA25 6 WG 210 333650
TA27 6 WG 210 333650
TA30 6 WG 260 232100
TA35 6 WG 310 231900
TA40 6 WG 310 217130