Operation and maintenance manual

Section 250-0065
Braking System - Two Speed Control Valve
SM 2159 7-02
2
WARNING
To prevent personal injury and property
damage, ensure wheel blocks and steering
locking bar is installed prior to executing
functional checks.
1. Position the vehicle in a level work area, apply the
parking brake and switch off the engine.
2. Disconnect electrical harness from temperature
switch at front axle manifold block (switch nearest
manifold block). Refer to Section 190-0270,
SWITCHES AND SENSORS.
3. Start engine and allow to idle.
4. Bridge connection on the temperature switch
harness. This will energise the solenoid cartridge (1) in
the two speed control valve.
5. Observe increase in disc brake oil cooler fan speed.
6. If fan speed does not increase, investigate fault on
two speed control valve solenoid cartridge (1) and
associated wiring.
FAULT DIAGNOSIS
Numbers in parentheses refer to Fig. 1. There are 4
possible points of failure:
1. Temperature switch failure. The disc brake oil
cooler temperature switch, mounted on the front axle
manifold block, should close when disc brake cooling
oil temperature rises above 50°C (122°F). Failure to
close will result in the solenoid cartridge (1) remaining
de-energised and the disc brake oil cooler fan will
remain at the slower speed setting. (Refer to
Functional Checks). Failure to energise the solenoid
cartridge (1) will result in higher disc brake cooling oil
temperatures.
2. The solenoid coil, although continuously rated they
may fail after long periods of service. Failure will be
evident as the higher speed operation of the disc
brake oil cooler fan will not be possible. (See
temperature switch failure above).
Solenoid Coil Rating: 14 W.
3. The cartridge valve (1) to which the solenoid is
attached. Failure is only likely to occur due to
contamination in the system. The valve is a low
leakage device and any contamination may cause
either damage to the components or cause
components to stick in position. Failure may be more
difficult to detect due to the different modes of failure.
Damage to the components will allow a progressively
increasing leakage, eventually resulting in some flow
not being shut off when the solenoid is energised.
Sticking components could hold the system at either a
low fan motor speed or a high fan motor speed,
depending on where the assembly has stuck.
4. Flow regulator cartridge (2). Contamination is the
only likely cause of failure, causing damage to the
relief valve seat. Failure will be difficult to detect as the
result of contamination damage is likely to be a
variation in the flow across the valve when the
solenoid is de-energised. This change of flow is
difficult to detect until it becomes very excessive.
Erratic disc brake oil cooler fan speed may be evident.
REMOVAL
Numbers in parentheses refer to Fig. 1.
WARNING
To prevent personal injury and property
damage, ensure wheel blocks, blocking
materials and lifting equipment are properly
secured and of adequate capacity to execute
the job safely.
1. Position the vehicle in a level work area, apply the
parking brake and switch off the engine. Operate
treadle valve continuously to relieve pressure in the
braking system.
2. Block all road wheels and place the battery master
switch in the 'Off' position. Place steering lock bar in
the 'Locked' position.
3. Remove guard from rear of disc brake oil cooler.
Refer to Section 210-0050, DISC BRAKE OIL
COOLER.
4. Remove blanking cap from remote drain line at the
bottom of the hydraulic tank. Install a length of hose on
remote drain fitting, open drain cock and drain
hydraulic oil into a suitable container. Close drain
cock, remove hose and reinstall blanking cap.
5. Clean two speed control valve and surrounding area
with a suitable solvent. Identify and tag all hydraulic
lines connected to two speed control valve, to aid in
'Installation'.
6. With suitable containers available to catch leakage,
disconnect hydraulic lines. Fit blanking caps to all