Hello Gents. Brand new to this forum. Thank you to John from "Farmcraft" Youtube channel for the link to this site. I have a 2002 Mustang 3503 mini excavator (Gehl/Wacker Nueson) I recently picked up that needed some tlc to bring her back to life. Long story short, I have no pilot oil pressure coming out of the pilot oil supply block outlet (BV). Consequently, the hydraulically released mechanical swing brake won't release and the machine will not swing. I can hear the pump load up when I move the joystick left or right, but the brake is locked because there's no pilot pressure at the release piston. I have proper pressure at all three pump inlets to the pilot supply oil block. I did find a teaspoon full of metal shavings in the main tank hydraulic filter that I suspect came from the scalded gear pump I subsequently replaced. All my hydraulic functions work as they're supposed to, except she won't swing because of the brake not disengaging. I've swapped the two pilot oil solenoids around to verify they both work. The problems seems to be a blockage in the pilot oil supply block, between where the pressure is entering and the pilot control oil output (BV). 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 is evidence of fluid in both solenoid valves when I removed them, but there's no pressure at the lower solenoid valve to direct. My next step is to remove the pilot oil supply block and dissasemble it on the bench to check for blockages. I'd appreciate any suggestions or tips that might point me in the right direction. Thanks, Rick.
Update: Removed and inspected pilot contol oil unit. Found no sign of contamination. I did find the pressure at P1 variable displacement pump only making 2200 psi max. It's supposed to max out at 3500 psi. Could that be why it's not getting through the safety valve in the pilot oil block rated at 725 psi? I only have half that pressure (350ish psi) at pilot oil outlet BV.
Update 2. Rebuilt variable displacement pump. Getting 3000+ at P1 now. Still only 350 psi at Pilot oil port BV, which only allows 350 psi at port PV to release the brake. (Supposed to be 500 +/- 80). So, either 350 psi is not enough to release the brake and the block is defective, or, I'm afraid I've got a bad swing drive unit. Does anyone know how to test the swing drive without removing it? I get 3000+ psi when I move the stick left or right, but I don't feel any hint of the house trying to swing. Pilot pressure only 350 psi. Seems like the brake is either locked tight, or my swing motor died. Would explain the two sizeable chunks of gear metal and metal shavings I pulled out of the hydraulic filter. Appreciate any suggestions. Thanks, Rick.