Aloha from hawaii. Long time lurker seldom do i ask for help but I need some advice. I've got a pc35mr-2 , all of the hydraulics are slow except the thumb. So far what I've done and checked is flow out of both pumps and have max 3 maybe 4 gpm as for pressure I have everything close to spec but just not the flow. So far I Teed in to the load sense circuit on the pump and I have 100 psi at idle in neutral and real close to circuit pressure on each individual circuit (bucket, boom etc). At full throttle going over relief. I checked the LS orifice and its free and clear as well as the in tank filter. A little back story on machine. A previous mechanic about 10 years back diagnosed the machine as having a bad pump with the same issue I'm having now. He replaced it and all was well until recently. Any one have any input?
Does your thumb circuit operates on a separate fixed-displacement circuit or bypass (not load-sensing controlled.) If yes, Low flow (3 to 4 GPM) with good pressure across all circuits except thumb = load-sensing system failure, not the pumps themselves. Your LS pressure readings says: 100 psi at idle/neutral is reasonable standby Going over relief at full throttle means the LS signal isn't commanding the pump to destroke -pump stays at max displacement and hits relief = no flow control What's wrong: LS compensator spool stuck: Internal contamination or wear prevents the pump from responding to load-sensing signals—pump can't modulate displacement properly Shuttle valve failure: PC35 uses shuttle valves to select highest pressure signal; if stuck, pump gets wrong LS command = poor flow distribution Main control valve LS ports: Internal wear or blockage prevents proper signal generation from each spool Critical test: Disconnect LS line at pump, plug it - pump should go to max flow/pressure (destroked) If flow doesn't increase significantly, the pump compensator is mechanically failed That "bad pump" 10 years ago probably wasn't bad - same LS system issue. Focus on compensator internals and shuttle valves before replacing pumps again.
Yes the thumb uses a fixed displacement circuit. Thank you for the detailed information. Ill be doing what you recommend later this afternoon and reporting back. I appreciate the info