Applicable Systems
EMCP 4.2
Symptoms
Complete loss of swing function. Swing brake does not release.
Possible Causes
- Swing motor brake solenoid coil open circuit.
- Swing relief valve stuck at high-pressure setting.
- Swing planetary gearbox seized due to lack of lubrication.
Troubleshooting Steps
- Step 1: Check solenoid coil resistance with multimeter.
Coil resistance 25–35 Ω; no open or short to ground. - Step 2: Measure swing circuit relief valve pressure at test port.
Relief pressure 34.3 MPa ± 0.5 MPa. - Step 3: Drain swing gearbox oil and inspect for metal fragments.
Oil clean with normal bronze wear dust only; no large chips.
How to Reset
Replace swing brake solenoid or relief valve; refill swing drive with SAE 80W-90 gear oil.
Common Replacement Parts
- Swing Brake Solenoid 191-1326: Swing Brake Solenoid 191-1326
- Swing Relief Valve 150-8225: Swing Relief Valve 150-8225
Frequently Asked Questions
- Q: Can I operate without swing brake?
No, swinging with locked brake will overheat and destroy the motor.
- Q: What oil goes in the swing drive?
Cat SAE 80W-90 gear lubricant or equivalent GL-5 spec.
Source: Caterpillar 320 Excavator Hydraulic System Manual
Category: Heavy Equipment