Hydrostatic Troubleshooting

Keep in mind:

1. Use proper safety protocols - the hydrostatic system operates at very high pressure and testing may result in unintended wheel movement.
1. Use proper PPE
2. Never work under or in close proximity to a running machine without accounting for possible unintended movements (elevate and stay clear of the wheels).
2. The system is highly susceptible to contamination. When removing hoses for testing – ensure the entire area and the environment is free from dust and debris.
3. When reassembling/installing new hoses and components:
1. Hoses must be rated for 6000 psi.
2. Do not mix aftermarket hose couplings with factory hoses. Hose couplings and hoses are a matched set to ensure performance at a given pressure over the life of the hose.
3. Ensure hoses are clean. If making the hoses locally (not preferred), thoroughly clean hoses before installation. The hydrostatic system is closed loop - meaning any contamination introduced to the closed loop will remain there, damaging components the entire time.
4. Bleed air from the circuit before driving the machine or wheel motor/pump damage may occur.
4. Document your troubleshooting by working down the attached hydrostatic troubleshooting worksheet, be sure to include:
   1. Last hydraulic oil replacement
   2. Last filter replacement
   3. Take a hydraulic oil sample – the issue could be caused by unsuitable hydraulic oil or there could be contamination
5. In general terms, check the pump first by isolating the pump from the diff-lock and wheel motors (remove large #12 hydraulic lines from the rear of the diff-lock manifold: plug the lines, cap the manifold – the pump should have perfect:
   1. Charge pressure
   2. Pedal pressure
   3. Servo control pressure
   4. Main pressure and
   5. Typically load the engine down from full throttle when dead headed
6. Once the pump is known to be good, then check the wheel motors for
   1. Case drain - Leak by should be less than 1 quart/30 seconds at full throttle and as much travel pedal as you can give the pump without spinning a wheel.
   2. Cross port leakage - Leak by should be less than 0.25 quart/30 seconds at full throttle and as much travel pedal as you can give the pump without spinning a wheel.
   3. In order to check all the pistons in the wheel motor, conduct both tests above with the wheel motors in two positions (mark the wheel/tire, rotate 180°, and retest).  
7. When replacing any hydrostatic component, flushing the system with a temporary high pressure flushing system is a must – P/N 500.055.1651.  This is a loaner tool which can be purchased and returned for credit.  Instructions on how to hook it up are included in the M50_M40 Service attachment.
8. Clean the inside of the hydraulic tank and replace the hydraulic oil and suction filters before installing a new pump
9. If the machine is also fitted with a purge valve (which moves hot oil out of the closed loop hydrostatic circuit), check the flow from the purge valve – about 4 quarts/30 seconds.