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Discussion Starter · #1 ·
Hoping to get some ideas and advice on an issue I am having with a John Deere Backhoe.
Here is a brief history on the machine and some information on the current issue.
1977 John Deere 310A with 6500 hours.
Same person that drove the machine off the trailer in 1977 has operated and supervised maintenance on the machine for all of those hours and now owns the machine. Machine has had no major mechanical issues until now. Current issue is that all hydraulic functions powered by the front pump have stopped completely. Machine will drive in all 8 gears in both forward and reverse. Seems to still have full power to the torque converter because, with the machine against a solid bank, the wheels spin from a dead stop in first and second and chokes the engine out above those gears.

We checked the pressure from the transmission/charge pump at the reverser valve port. Pressure reads 150psi at cold (25 degrees outside) start up and drops to roughly 146 after warm up. Maintains 146 with reverser in neutral, forward and reverse through all 8 gears. Pressure drops to 75 and jumps right back up to 146 when shifting between neutral, forward and reverse.

We have completed the following to try and fix the issue.
Replaced main front pump including de-stroke solenoid valve and rubber parts of drive coupling. No worn splines or evidence of connection slipping found.
Drained old fluid, changed both filters, cleaned sump screen, refilled then ran the machine to flush system and changed filters and screen again before installing new pump.
Removed, cleaned, inspected and reinstalled all relief valves externally accessible on the transmission, all three relief valves on the backhoe and the one relief valve on the loader including new seals/o-rings.
Removed, cleaned and rebuilt reverser valve with all new seals, 0-rings, valve spools and grove pins.
Removed, cleaned and rebuilt priority valve with all new seals and o-rings.

Absolutely zero change after all of this work.

Am in the process of installing fittings to accommodate pressure gages in various locations to see if we can find where the pressure drop is happening.
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