No oil pressure

[willhoff]

I have a JD 6405 with a SyncroPlus Transmission. The transmission had 75 psi of oil pressure which is low. I pulled the transmission. Everything looks good so I put a new pump, seals, O-ring in the unit and put it back together. I started the tractor everything worked good. I shut the engine off and topped the transmission oil off then started the tractor again. It wouldn't move. I have zero oil pressure. I pulled the transmission again and everything looks good. Any Suggestions??

 

[WranglerX]

Air pocket in system (cavitation in pump?), any way to purge the pump and lines?

Dale

 

[willhoff]

Air pocket in system (cavitation in pump?), any way to purge the pump and lines?

Dale

I didn't hear the pump cavitating when it was running and the pump was working for a time. The oil pressure check point is basically beside the pump so there is no oil lines to bleed. I wouldn't think air could be trapped in this system.

 

[Stimw]

Relief valve stuck open?

 

[willhoff]

Relief valve stuck open?

It looks like there is two valves that regulate the oil pressure in that transmission. It has a Pressure Regulating Valve and a Engagement Override Valve. I disassembled both valves. The spools where clean, no marks or scratches and they moved freely in their ports. The springs looked good and they measured the specified length. I don't have a way to test pounds of torsion on the springs but I was satisfied they are not at fault and put the valves back together.