Group 29, Hydraulic Sump, Filters, and Pump
29-2-2 • Main Hydraulic Pump Troubleshooting SM 765, Nov ’06
The following is a list of problems and solutions relating
to the main hydraulic pump and associated components.
For other hydraulic system troubleshooting, refer to
Groups 30 and 34.
Noisy Pump
• Hydraulic fluid level low; measure and correct
fluid level.
• Fluid viscosity too high; change to specified fluid.
• Sump strainer dirty; check and clean.
• Air leak at pump inlet line; check plumbing tight-
ness.
• Inlet line restriction; check for foreign material or
line kinks, check and clean sump suction screen.
• Air leak at pump shaft packing; replace packing.
• Defective hydraulic pump; continue other trouble-
shooting items, then consider servicing or replac-
ing pump.
Pump Not Delivering Hydraulic Fluid
• Hydraulic fluid level low; check and correct fluid
level.
• Sump suction screen dirty; check and clean.
• Inlet line restriction; check for foreign material or
line kinks, check and clean sump suction screen.
• Air leak in suction line: check plumbing tightness.
• Fluid viscosity too high: check fluid viscosity and
change to specified fluid.
• Defective hydraulic pump; continue other trouble-
shooting items, then consider servicing or replac-
ing pump.
Failure to Build Pressure
• Hydraulic fluid level low; measure and correct
fluid level.
• Defective relief valve or pump: perform pressure
check to test valve and pump.
Pump Not Developing Sufficient
Pressure
• Leak in hydraulic control system; check system for
and correct leaks.
• Inlet line restriction; check for foreign material or
line kinks, check and clean sump suction screen.
• Suction screen dirty; clean screen.
• Defective hydraulic pump; continue other trouble-
shooting items, then consider servicing or replac-
ing pump.
Pump Output Low
• Cavitating pump; see “Noisy Pump.”
• Air in fluid or wrong fluid; drain and fill with cor-
rect fluid.
• System relief valve set too low or too high, stuck or
leaking; correct relief valve, pump may be OK.
• Overheated fluid; see “Overheated Pump and/or
Fluid.”
• Contaminated fluid; eliminate contamination
source and replace fluid.
• Gear face, body or cover nicked; repair or replace
pump.
• Excessive side loading, wear plate tight in body
bore, pinched thrust plate; inspect and service
pump.
Foaming Fluid
• Cavitating pump; see “Noisy Pump.”
• Wrong fluid; drain and fill with correct fluid.
Overheated Pump and/or Fluid
• Low viscosity fluid; drain and fill with correct
fluid.
• Contaminated fluid; drain fluid, clean suction
screen, replace filter and fill sump.
• Cavitating pump: see “Noisy Pump.”
• Pump drive shaft misaligned; check mounting and
alignment.
• Axial loading on drive shaft; check shaft end clear-
ance and shaft alignment; check for worn key/
spline.
• Relief valve usually in bypass; check relief setting.
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