Trouble Shooting
In trouble shooting a pump and motor system it is necessary to isolate the pump from the motor to determine which unit is
actually malfunctioning. A worn pump or worn motor will give the same system indication. Therefore, it is advisable to first run a
pressure and flow check on the pump to make sure it is performing within its operating specifications. The following trouble
shooting suggestions are based on the assumption that the pump’s flow and pressure settings meet operating specifications.
Possible Trouble
1. Motor turns while unloaded but
slows down or stops when
load is applied.
2. Motor will not turn.
3. Motor free wheels.
4. Rapid tapping noise in motor.
5. Excessive case drain flow.
Causes
A. Scored back plate.
B. Scored connector plate.
C. Scored or worn piston shoes.
D. Low relief valve pressure.
A. Severely scored back plate
and connector plate.
B. Contaminate particle holding
connector off back plate.
A. Oil flow and pressure shut off
going to motor.
A. Free floating pistons seating
on bearing race.
A. Excessive internal wear in.
Remedies
A. Remove backplate and examine surface condition of flat area, if
scored, replace back plate. Do not lap.
B. Disassemble motor, check finish on connector plate and back
plate, replace of necessary.
C. Disassemble motor, examine condition of shoes on pistons,
replace pistons as a complete set.
D. Check relief valve for proper pressure setting, adjust or replace
relief valve.
A. Disassemble motor completely. Inspect all parts, clean all parts,
replace all worn parts and flush hydraulic system.
B. Disassembly motor, inspect and clean parts, replace necessary
parts.
A. When the hydraulic system is shut off, either by shutting off the
engine on a closed loop system or returning the control valve
spool to neutral on an open center system, the motor will free
wheel after it has leaked off and allows the free floating pistons to
collapse. This is inherent in the design. On a closed loop or
propulsion system, the motor will not free wheel as long as
charge pressure is maintained to and from the motor.
A. When oil flow to the motor is shut off and the motor allowed to
free wheel, the free floating pistons will collapse into the piston
block. When oil flow is reapplied to the motor the pistons will re-
seat themselves against the bearing race and will cause a rapid
tapping sound. This is not harmful to the motor as long as the oil
flow into the motor does not exceed 10 GPM for the first
revolution of the motor.
A. Disassemble motor, inspect parts and replace as necessary. Case
drain flow should not exceed 1.5 GPM at full pressure.
