Harry in Ky
Member
- Location
- Central Kentucky
I'm back on this 6640 today. I've replaced both the engine mounted and internal gear pumps now, and finally got it running again. The pumps are now working but there is another problem. It may well be what caused the pump failures to begin with, but I don't remember it doing this when I worked on it last. It has a loader supplied from the deluxe remote valves. When the remotes are activated the loader operates but when the valves are returned to neutral the pressure in the combined flow of the pumps doesn't drop off as it should.
I was expecting something wrong here to help explain what took out both pumps, so I have pressure gauges tied into both pump outputs to monitor each one separately while I check things out. The lift seems to work without a problem, and the loader does too as long as I move the levers just so far in all directions. If I open one valve too far the pressure on both pumps jumps to relief setting, no matter what position the valves are placed in. The pressure will not drop until I shut the motor off. I can start it back up and the pressure is gone until I start moving the valve levers again. I did this probably a half dozen times with the same results.
I've been going through the hydraulic sections on forty series tractor service manual and came to a section describing a portion of the system that might be in play here.
A brief description stating that activation of a remote valve applies the load sensing signal to the end of the spool of the combining valve and blocks off the pump output flow to sump (assuming that means it will build pressure as required?)
When the remote valve is returned to neutral the sensing line is vented, so pump pressure then moves the combining valve back the other way and pump pressure/flow is returned to sump. It seems that maybe this isn't happening?
Now I wonder just how to check for that and/or prove that it is or isn't.
I was expecting something wrong here to help explain what took out both pumps, so I have pressure gauges tied into both pump outputs to monitor each one separately while I check things out. The lift seems to work without a problem, and the loader does too as long as I move the levers just so far in all directions. If I open one valve too far the pressure on both pumps jumps to relief setting, no matter what position the valves are placed in. The pressure will not drop until I shut the motor off. I can start it back up and the pressure is gone until I start moving the valve levers again. I did this probably a half dozen times with the same results.
I've been going through the hydraulic sections on forty series tractor service manual and came to a section describing a portion of the system that might be in play here.
A brief description stating that activation of a remote valve applies the load sensing signal to the end of the spool of the combining valve and blocks off the pump output flow to sump (assuming that means it will build pressure as required?)
When the remote valve is returned to neutral the sensing line is vented, so pump pressure then moves the combining valve back the other way and pump pressure/flow is returned to sump. It seems that maybe this isn't happening?
Now I wonder just how to check for that and/or prove that it is or isn't.