I’ve been chasing a problem in my 4620 hydraulic system and getting nowhere with it. The tractor works almost perfectly in winter in the feeder car when the oil is cold. Most people would not even notice a problem. But if I put it in my hay crusher and it gets hot, the hydraulic system rattles terribly and the conveyor speeds up and slows down, even once it came to a complete stop and I had to move the hydraulic valve back and forth several times to to get going. Now that it’s warmer, the hydraulics won’t stop flashing. Yes, it is always full of oil. I did a complete oil and filter check. The mesh was totally clean. The hydraulic pressure has been at 2400 psi with no problem but if I crank a second valve with the hose routed inside the valve just for it to flow my pressure drops to 500 psi and the priority valve is the culpert of the talk. I checked the transmission pump, a lot of pressure filled a 5 gallon bucket in 25 seconds, I checked the line going into the pump, the same, I thought fine, the pump gives me pressure but no flow, possible problem inside, replacement the main hydraulic pump, problem not solved, I have inspected through the plug in the back of the rear for leaks and have not seen anything with light. The steering and brakes work fine, if I flow with the scv valve the PTO squeaks as it does not have enough pressure for the clutch. Obviously I have a leak somewhere and I’m chasing but not much luck searching, right now I have the priority valve off to inspect, but everything looks good, there are three wedge washers in it with the spring. I have felt the pipes but I have not felt heat, but I have not worked with the tractor since it is in the workshop. Also this tractor is a power shift.
Hydraulic system is running out of functional return oil to hydraulic pump. Based on your description of the problem, what work have you done, knowing this is a PS transmission and if you are not seeing oil leaks inside the differential case, the next most likely place for the return oil leak to the crankcase would be hydraulic return filter relief valve functional (rear).
This filter has its own filter relief valve located at the base of the rear filter cavity. If this valve is left open, return oil from all rear hydraulic functions will be directed to the crankcase, causing a lack of return oil to feed the main hydraulic pump. These systems must have all the return oil for the main hydraulic pump to meet its normal pumping capacity. It is recommended to drain the hydraulic oil from the rear, remove the rear hydraulic filter, remove the three screws holding the relief valve housing at the rear of the filter cavity, and inspect the valves and springs in this housing / set.