jcb ROBOT 150, Service Manual

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10 - 7
Section E
Hydraulics
9803/8500
Section E
10 - 7
Issue 2
Pumps
Fault Finding
Servo machines up to serial no. 676354
Machine veers to one side when travelling.
Servo unit adjustment
The diagram shows the main pump servo units when viewed
from the side door of the cab.
Note: The servo unit adjuster screws are normally set to
allow 5 mm gap when pump piston is at full swash. Therefore
to limit piston travel it is necessary to screw in the grubscrews
by approximately 5 mm before adjustment can take place.
If the machine does not travel in a straight line, proceed as
follows:
Fault
1 Machine veers excessively to left in forward travel
2 Machine veers excessively to right in forward travel
3 Machine veers excessively to left in reverse travel
4 Machine veers excessively to right in reverse travel
Loosen locknut on adjuster screw A , screw in grub screw
approx. 5mm and tighten locknut. Try machine. Keep
adjusting
2
turn at a time until straight line travel is achieved.
Proceed as for fault 1 but adjust screw D .
Proceed as for fault 2 but adjust screw B .
Proceed as for fault 3 but adjust screw C .
A A C C
B B D D
This condition may be corrected by adjusting the pump servo units but before attempting this, carry out the following preliminary
checks.
Check tyre pressures The pressure of one tyre may be low or one or both tyres on one side of the machine may be new
and condition and the other tyres worn. In both these cases the rolling circumference of the tyres will be unequal
causing the machine to veer to one side.
Check chain tension Chains which are tensioned unequally will cause the machine to veer to one side. Always adjust the
tension on all four chains, never just one.
Check brake release Low pressure or faulty seals may cause the brake to drag on one side. Check the pressure at the
pressure, seal failure anti-stall valve. Check the seal by using a hand pump to release the brake and see if the pressure
holds.
Check the drive joystick Check that the joystick spools are not sticking and are correctly operated by the lever.
Note: If the fault cannot be rectified by any of the above checks or adjustment, then either the pump or motor could be faulty. To
identify which, swop the motor feed hoses at the pump. If the machine now veers in the opposite direction then the pump is
faulty. If the machine continues to veer in the same direction the the motor is faulty.