Operation and maintenance manual

Section 250-0075
Braking System - Priority Unloader Valve
SM 2161 7-02
2
2. Start truck and allow pressures to increase with
engine at low idle, until all warning lights are
extinguished.
3. Take note of the gauge reading; this is the pressure
setting of the priority unloader valve. Valve should be
set at 170 bar (2465 lbf/in²).
4. If pressure setting is too low after following steps 1
through 3:
(a) Ensure engine is operating at low idle.
(b) Loosen lock nut on unloader relief valve (1).
(c) Turn setting screw on unloader relief valve (1)
clockwise (CW) until correct pressure is observed on
gauge.
(d) Re-tighten lock nut.
Note: Always adjust hydraulic pressure on the
increase.
5. If pressure setting is too high after following steps 1
through 3:
(a) Stop engine and operate treadle valve continuously
to dissipate pressure in brake accumulators.
(b) Loosen lock nut on unloader relief valve (1).
(c) Turn setting screw on unloader relief valve (1)
counter clockwise (CCW) 2 to 3 full turns.
(d) Re-start engine and allow pressures to rise with
engine at low idle, until all warning lights are
extinguished.
(e) Turn setting screw clockwise (CW) until correct
pressure is observed on gauge.
(g) Re-tighten lock nut.
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 the steering lock bar
in the 'Locked' position.
3. 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.
4. Clean priority unloader valve body (3) and
surrounding area with a suitable solvent. Identify and
tag all hydraulic lines connected to the priority
unloader valve, to aid in 'Installation'.
5. With suitable containers available to catch leakage,
disconnect hydraulic lines. Fit blanking caps to all
open lines.
6. Remove bolts and lockwashers securing the priority
unloader valve to the hydraulic cradle. Remove priority
unloader valve.
DISASSEMBLY
Numbers in parentheses refer to Fig. 1.
It is not recommended that any of the cartridge
assemblies are disassembled for maintenance
purposes. Ensure that valve assembly is cleaned off
prior to removal of any components and that no
contaminant is allowed to enter the internal galleries.
1. Note location and position of all hydraulic
connectors and adaptors prior to removing them from
valve body (3).
2. Remove unloader relief valve (1). Check for wear,
scoring or contamination.
3. Remove check valve (2). Check for wear, scoring or
contamination.
ASSEMBLY
Numbers in parentheses refer to Fig. 1.
1. Replace all 'O' rings on hydraulic connectors and
adaptors.
2. Replace all seals on unloader relief valve (1) and
check valve (2) prior to assembly.
3. Locate unloader relief valve (1) in valve body (3)
and tighten to 95 Nm (70 lbf ft).
4. Locate check valve (2) in valve body (3) and tighten
to 95 Nm (70 lbf ft).
5. Install hydraulic connectors and adaptors to correct