Section 250-0070
SM 1939 4-00
3
Thereafter, relay piston (5) will operate the inlet/
exhaust valve (2) as previously described.
Apart from the reduced vehicle braking efficiency, the
effect of a loss of air pressure from No. 1 circuit will
be a small increase in the operating plunger travel
and a moderate increase in the effort required to
depress the brake treadle.
REMOVAL AND DISASSEMBLY
Numbers in parentheses refer to Fig. 1.
WARNING
To prevent personal injury and property
damage, be sure wheel blocks are properly
secured and of adequate capacity to do the job
safely.
1. Position the vehicle in a level work area, apply the
parking brake and switch off the engine.
2. Block all road wheels and place the battery master
switch in the 'Off' position.
3. Open drain cocks on air tanks and drain air from
three main air tanks and auxiliary air tank. Close
drain cocks on air tanks when air is exhausted.
4. Remove mounting hardware securing toe plate
assembly to the cab floor.
5. Manoeuvre the toe plate assembly to allow access
and tag and remove all air lines from the treadle
valve assembly.
6. Release and remove mounting hardware securing
treadle valve assembly to the toe plate assembly.
7. Remove treadle valve assembly from the vehicle.
8. If required, separate valve body (1 & 8) assembly
and treadle (26) assembly.
Note: The treadle valve assembly should not be
disassembled further as replacement of parts is by
treadle (26) assembly and/or valve body (1 & 8)
assembly only. Refer to 'Maintenance' procedures.
ASSEMBLY AND INSTALLATION
Numbers in parentheses refer to Fig. 1.
Note: Tighten all fasteners to standard torques listed
in Section 300-0080, STANDARD BOLT AND NUT
TORQUE SPECIFICATIONS.
1. If removed, install treadle (26) assembly on valve
body (1 & 8) assembly.
2. If removed, install treadle valve assembly to the
toe plate with mounting hardware, as removed at
'Removal and Disassembly'.
Note: Treadle valve is the left hand pedal on the toe
plate.
3. Install all air lines to the treadle valve assembly,
as tagged at removal.
4. Place the battery master switch in the 'On'
position, start the engine and allow air pressure in the
tanks to build up to correct operating pressure.
Check for leaks at air lines and tighten as required.
5. Secure toe plate assembly to the cab floor with
mounting hardware, as removed at 'Removal and
Disassembly'.
6. Remove wheel blocks from all road wheels.
ADJUSTMENTS
Numbers in parentheses refer to Fig. 1.
If the treadle valve does not release promptly or does
not fully release, it indicates that exhaust valve is not
opening sufficiently. This can be caused by:
1. Lack of lubrication in valve body causing piston
and spring assembly to bind.
2. Dirt or other foreign matter between the heel of
treadle (26) and mounting plate (28).
If the treadle valve does not apply promptly, or does
not apply fully, it indicates that inlet valve (10) is
not opening sufficiently. Check for correct operation
and replace valve assembly, if required.
Braking System - Treadle Valve
Courtesy of Machine.Market
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