Section 12: BRAKE AND AIR SYSTEM
PA1562
28
CAUTION
In order to protect the ABS electronic control
unit from voltage surges, always disconnect
before performing any welding procedure on
vehicle.
31.3.2 ABS Modulator Valve
This ABS system is equipped with four or five
modulator valves, located between the brake
chamber and the relay valve or quick release
valve (Fig. 45). Note that on the basic ABS
system, there is only one solenoid valve
controlling the drive and tag axle wheels on the
same side (tag axle is slave to drive axle).
FIGURE 45: ABS MODULATOR VALVE 12221
This is an "On/Off" type valve, i.e., at brake
application, the valve exhausts air from the
brake chamber when the electronic unit senses
that the corresponding wheel speed is
decreasing in relation to the other wheels.
Maintenance
Refer to Bendix Service Data sheet SD-13-4870
located at the end of this section.
31.3.3 Sensors
The sensors are mounted on the front, drive and
tag axle (if applicable) wheel hubs (Fig. 46). The
inductive sensors consist essentially of a
permanent magnet with a round pole pin and a
coil. The rotation of the toothed wheel alters the
magnetic flux picked up by the coil, producing an
alternating voltage, the frequency of which is
proportional to wheel speed. When wheel speed
decreases, magnetic flux decreases proportion-
ately. Consequently, the electronic control unit
will command the solenoid control valve to
decrease the pressure at the corresponding
brake chamber.
Maintenance
No specific maintenance is required for sensors,
except if the sensors have to be removed for
axle servicing. In such a case, sensors should
be lubricated with special grease (Prévost
#680460) before reinstallation. Refer to
paragraph “Sensor Installation” for details.
FIGURE 46: ABS SENSOR LOCATION 12153
NOTE
The resistance value, when sensors are
checked as a unit, must be equal to 1,75 k
ohms. To check the sensors for proper output
voltage after the sensors and toothed wheels
have been assembled to the axle, connect a
suitable AC voltmeter across the output
terminals. With the hubs rotating at 30 rpm,
the output voltages should read from 50 to
1999 mV to be acceptable.
Sensor Installation
The following procedure deals with sensor
installation on the axle wheel hubs. Read
procedure carefully before reinstalling a sensor,
as its installation must comply with operational
tolerances and specifications.
1. Apply recommended lubricant (Prévost
#680460) to spring clip and sensor.
To Next Page
Loading...