Mustang 742, 744, 944, 1155 Telehandler Service Manual (incl. Wiring)

Check the hydraulic reservoir fluid level first — capacity is 170 L (page 15). If fluid is good, verify main relief pressure is at 3000 PSI (page 19); low pressure points to a worn pump or stuck relief valve. Inspect the 15-micron filter element for contamination; bypass opens at 45 PSI (page 19), so a clogged element starves the system. Then work through the boom lift troubleshooting chart to isolate cylinder seals versus valve faults.

Start at the starter circuit troubleshooting procedure on page 49. Check battery terminal connections and verify the starter relay — relay mounting bolts torque to 40 to 45 lb ft (54 to 61 Nm). Confirm fuel tank has adequate supply; tank capacity is 114 L (page 15). If cranking speed is weak, load-test the battery and check ground straps before condemning the starter. Cold-weather no-starts with adequate fuel usually trace to glow plug circuit — test per the electrical schematics beginning page 61.

Check transmission fluid level against the 11.3 L capacity spec (page 16) and inspect for burnt smell or discoloration. Verify transfer case oil is at the 2.8 L mark (page 16). If fluid checks out, confirm pilot pressure is within spec using the Control and Park Brake Pilot Pressure troubleshooting procedure — low pilot pressure kills both drive and brake release. Transmission and transfer case mounting bracket bolts should be torqued to 285 to 320 lb ft (385 to 435 Nm) per page 108; loose mounts cause driveline vibration that mimics transmission slip.

Run the boom extend cylinder troubleshooting sequence. Inspect cylinder seals for bypass — internal leakage lets the load settle even with the control valve centered. Check the hydraulic schematic to confirm extend circuit routing and verify auxiliary relief pressure is at 2500 PSI (page 19); low auxiliary relief allows premature bypass. If you're pulling the cylinder for seal replacement, the hydraulic filter rated flow is 70 GPM (265 L/min) — confirm flow returns to spec after reassembly before closing up.

Work through the Park Brake Circuit Troubleshooting procedure on pages 51-52 before touching hardware. Verify pilot pressure reaches the SAHR valve using the check procedure — the park brake is spring-applied, hydraulic-release, so low pilot pressure keeps it dragging. Inspect the brake circuit solenoid wiring against the schematics starting page 61. If pilot pressure is confirmed good and brake still drags, the issue is mechanical: inspect disc wear and SAHR valve seals per the hydraulic system teardown procedures.

Begin with the Steering Mode Circuit Troubleshooting procedure on page 54 to isolate whether the fault is electrical (mode solenoid, switch, wiring) or hydraulic. Verify steering system pressure is at 2500 PSI (page 19) — low pressure prevents mode shifting. Pull up the Steering Circuit Troubleshooting chart to check front and rear steer cylinders individually. If solenoids are suspect, test coil resistance against the wiring diagram on page 61 before ordering parts; a failed mode switch feeds the same symptom as a dead solenoid.