Hydraulic Pump And Motor Assembly; 9-5.1. Pump And Motor Assembly Removal; 9-5.2. Hydraulic Pressure Adjustment; Lift Cylinder Repair - Big Joe PDBB-20-T12 Operation, Maintenance, Repair Parts List

9-5. HYDRAULIC PUMP AND MOTOR ASSEMBLY.

A defective hydraulic pump must be replaced as a
complete unit, but the pump motor can be repaired
(see SECTION 10, Electrical Components Servicing.

9-5.1. Pump and Motor Assembly Removal.

WARNING: Before disconnecting any hydraulic lines,
make sure the forks are lowered com-
pletely and the system is not under pres-
sure.
1. Disconnect battery.
2. Drain hydraulic oil from reservoir into suitable
container.
3. Label, then disconnect wires from solenoid.
4. Label, then disconnect tubing (39,
hose (23) from the pump and motor assembly (2).
5. Remove the pump and motor assembly by remov-
ing the two screws (5), two lock washers (8) and
two flat washers (7).
6. To separate the pump from the motor, remove the
four hex head screws that connect the pump to
the motor end housing.
NOTE: When reassembling the pump to the motor,
always use a new gasket.

9-5.2. Hydraulic Pressure Adjustment.

WARNING: Improper setting of the hydraulic pump
pressure by an unauthorized person can
damage the hydraulic system and void
your warranty.
NOTE: The hydraulic pump is factory set to lift a load
at the rated capacity of the truck. The pres-
sure relief valve should rarely need adjust-
ment. If the truck fails to lift a load that is
within the truck capacity rating, adjust as fol-
lows:
1. Remove the cap nut from the hydraulic pump.
2. Insert a screwdriver blade in the screw slot.
CAUTION: Do not set pressure any higher than that
required to lift a load of the rated capac-
ity of the truck.
901357
3.
4.

9-6. LIFT CYLINDER REPAIR.

NOTE: Removal procedures are covered in
CAUTION:
1.
Figure 9-1) and
2.
3.
CAUTION:
4.
5.
6.
NOTE: Install packing kit 907123.
7.
8.
9.
CAUTION:
10. Secure lift cylinder tube (1) in vise.
11. Install cylinder ram (5) into cylinder tube (1).
12. Install new O-ring (4) and wiper ring (2) on gland
13. Install gland nut (3) in cylinder tube (1).
14. Remove lift cylinder assembly from vise.
Turn the screwdriver clockwise to increase
hydraulic pressure; counterclockwise to decrease
pressure.
Install the cap nut on the hydraulic pump.
TION 8.
To prevent cylinder damage, use proper
pipe clamp vise. The cylinder will be dis-
torted if the vise is tightened too much.
Secure lift cylinder assembly in a vise and remove
gland nut (3, Figure 9-2) with wiper ring (2) and O-
ring (4).
Pull out cylinder ram (5).
Remove lift cylinder tube (1) from vise.
To prevent damaging the finish on the
ram, use proper pipe clamp vise with
non-marring jaws.
Secure ram (5) in vise.
Remove nut (11).
Pull off piston (14) and O-ring (7). Remove seal
(15) from piston (14).
Coat seal (15) and piston (14) liberally with petro-
leum jelly. Install new seal (15) on piston (14).
Install new O-ring (7), piston (14), and nut (11)
onto cylinder ram (5).
Remove cylinder ram (5) from vise.
To prevent cylinder damage, use proper
pipe clamp vise. The cylinder will be dis-
torted if the vise is tightened too much.
nut (3).
SEC-
9-3