SERVICE MANUAL
Trailer Charge (Fig. 7)
If both valves are out, parking the combination
vehicle, and it is desired to recharge the trailer leaving
the tractor spring brakes applied, the red knob may be
pushed in repressurizing the trailer supply line. This
mode may also be used to park a combination vehicle
with tractor spring brakes only.
Automatic Application
With both knobs in, as in the normal run position
(Fig. 8 ), and supply pressure to the push-pull valves is
reduced to 276 27.6 kPa (40 5 psi), the red knob
(trailer supply valve) must pop out, applying the
emergency or parking brakes on the trailer. If the red
knob is held in manually and the pressure decreases to
207 27.6 kPa (30 5 psi), a tripper piston within the
trailer control spool will move upward, exhausting the
trailer air supply, thus applying the trailer brakes.
Fig. 8 Normal Operating Position
Normal Run Position (Fig. 8)
With both knobs pushed in, air is now being supplied to
the trailer and to the tractor spring brakes; all brakes are
released.
Actuation or Trailer Park or Emergency Brakes (Fig.
9)
To actuate the trailer brakes only, the red knob is
pulled out, exhausting the trailer supply line. The trailer
brakes are now applied either by emergency air or spring
brakes, depending on the type of trailer system. This
mode would be used to uncouple from the trailer and
during bob-tail operation.
Fig. 9 Park Trailer with Tractor Released or Bobtail
Tractor
MAINTENANCE
Once each year or every 160,000 km (100,000
miles) the modular control valve should be disassembled
and
thoroughly
cleaned.
Replace
all
components
supplied with the repair kit.
Lubricate all components with lubricant listed in
LUBRICANT SPECIFICATIONS, Item 3.
Perform the Service Checks after rebuilding valve
assembly.
SERVICE CHECKS
When the service checks on the modular control
valve are performed on the vehicle, both the Leakage
and
Operating
checks
will
be
accomplished
simultaneously.
In some instances it will be necessary to remove the
instrument panel bezel and the access panel on the
instrument panel to gain access to the valve. Block or
hold vehicle by means other than the parking brake while
performing the Service Checks.
1.
With both control knobs out, charge the air brake
system to 448 kPa (65 psi), and check for
leakage. No leakage permitted.
2.
With supply pressure still at 448 kPa (65 psi),
push the red knob in. The knob must stay in.
Leakage at the exhaust port must not exceed a
25 mm (1") bubble in 5 seconds.
3.
Push the yellow knob in. With the engine off
apply the foot valve several times to deplete the
air supply. The red knob must pop out
CTS-4079 - CHAPTER VII - Page 8
