2002 Mustang 3503 mini excavator (Gehl/Wacker Nueson). House won't swing. I have only 250 psi pilot oil pressure coming out of the pilot oil supply block outlet (BV) when left stick is moved left or right, and consequently, low/no pressure at outlet (PV) as well. I don't think it's enough pressure to hydraulically release the mechanical swing brake. It won't release and the machine will not swing. I get 3200 psi at P3 (gear pump) and can hear the pump load up when I move the joystick left or right, but only 250ish psi at the (BV) outlet. I think the brake is locked because there's not enough pressure at the release piston (PV). I have proper pressure at all three pump inlets to the pilot supply oil block. All my hydraulic functions work as they're supposed to, except she won't swing, and the auxillary hydraulics won't switch between the thumb function and the boom swivel function. Which I think is also related to the low pilot pressure. I've swapped the two pilot oil valves and solenoids around to verify they both work. Both are getting 12volts with left armrest down. The problem seems to be a blockage in the pilot oil supply block, between where the pressure is entering and the pilot control oil output (BV). (Blocked shuttle valve, or failed pressure reduction valve, maybe?) There's supposed to be a way to adjust the pilot pressure at the pressure reduction valve but I can't tell how to adjust it. Metal rings?) I've removed the (BV) fitting, pressure reduction valve cap, and safety valve cap, on the block, and probed them with a magnet but found no sign of metal or blockage. There was evidence of fluid in both solenoid valves when I removed them. It should probably be noted that when I lift the left armrest, the dozer blade and auxillary hydraulics continue to operate, while all other hydraulics are inoperable, as they should be. She also doesn't load up when I try to swing the house with the armrest up, which indicates the safety solenoids are working. Why the dozer blade and AH work when the safety solenoid is open remains a mystery. lol. I'd appreciate any suggestions or tips that might point me in the right direction. Thanks, Rick.
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