Applicable Systems
9R Tractor
Symptoms
Loader bucket does not curl or dump smoothly; jerky motion observed.
Possible Causes
- Bucket cylinder piston seal worn causing pressure bypass.
- Main relief valve pressure set too low or spring fatigued.
- Hydraulic oil aerated due to suction leak on pump inlet.
Troubleshooting Steps
- Step 1: Hold bucket against pile and check rod-side pressure gauge.
Pressure holds steady at 24 MPa; no decay. - Step 2: Measure main relief valve cracking pressure at test port.
Relief opens at 24.5 MPa ± 0.7 MPa. - Step 3: Inspect suction hose between tank and pump for collapsed inner liner.
Hose firm, no vacuum collapse; clamps tight.
How to Reset
Re-seal bucket cylinder; adjust or replace main relief valve; replace suction hose if collapsed.
Common Replacement Parts
- Bucket Cylinder Seal Kit RE18158: Bucket Cylinder Seal Kit RE18158
- Main Relief Valve RE17185: Main Relief Valve RE17185
Frequently Asked Questions
- Q: Can aerated oil damage the pump?
Yes, cavitation from air bubbles erodes pump plungers and housing.
- Q: What is normal hydraulic pressure for 644K?
Main relief: 24.5 MPa; pilot: 3.4 MPa.
Source: John Deere 644K Loader Hydraulic Manual
Category: Heavy Equipment