Johnston VM502, Maintenance Manual

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MA9:7
V Range 502
l
652
l
802 Maintenance Manual
Johnston Sweepers Limited
Chapter - Service Tools
Motor Set-Up - Pressure Control Adjustment
The motor is equipped with two in-built pre-set control features:
1 Threshold Control.
Instigates a decrease in the motor displacement resulting from a signal from the main control
valve in the pump.
2 Pressure Compensator Override (PCOR).
Instigates a increases in the motor displacement resulting from higher circuit pressure.
Both these controls are pressure sensitive and factory set and on this basis should not be adjusted. However,
to ensure conformity we like to check the displacement actuation pressure. This is achieved by connecting
suitable pressure gauges (40 bar) to test point
T4B with Hydrodrive engaged, handbrake released, select
forward drive and using the hand held PPU on position C2 , slowly increase its value until a road speed of
between 8-10 km/h is reached, at the same time observing the reading on pressure gauge, it should be 24
bar, until 8-10 km/h is reached. At this point the pressure should start to reduce.
The object of this test is to ensure the pump boost pressure (24 bar) is maintained at
T4B until the speed
criteria is achieved when motor displacement starts to change.
Sectioned view of transmission motor
M02MA-047-2
1
2
3
4
5
6
Control Pressure Port
Hydraulic Proportional Control
Pressure Compensator Override
Minimum Displacement Limiter
Valve Segment
Bearing Plate
Tapered Roller Bearings
Synchronizing Shaft
Piston
Change Pressure Relief Valve
Servo Piston Cylinder
7
8
9
10
11
4
3
2 1
5 6 7
8 9
10
11
Completion of Setup
Remove guarding. Lower the vehicle off the axle stands and road test the vehicle in hydrostatic drive to
confirm 40 kph can be achieved along the flat and that the vehicle can climb hills in Forward and Reverse.
Please note max speed in reverse along the flat is restricted to 10 kph approximately.