310 Backhoe Hydraulics

[310farmer]

I purchased a 1974 310 with 6200 hours on it a couple of months ago to use on my farm. Before I used it I changed all of the filters and fluids. I have never used a backhoe before, but it seems like the hydraulics have a volume problem. Everything moves fine if I move one thing at a time, but if I try to raise the loader while tilting the bucket, or curl the backhoe bucket while swinging the boom,or any other multiple movement, the movements become very slow and it is faster just to move things one axis at a time. I should add that the pump shaft seal has gone out and the pump is currently sitting disassembled on my work bench waiting on a seals kit and new shaft. I have been reading this forum and have since learned of the long screen that is inside the transmission, but it only had a minimum amount of sludge on it. Are there any other things I should check out while the system is drained and apart?

 

[Roy Suomi]

Filter relief valves have been a problem for many years on the older machines...It doesn't take much...Just a nearly microscopic piece of crap sticks the filter relief valve partially open dumping oil back to sump, starving the pump..It's located just above the vertical filter..You can see it from underneath with filter off..Shiney chrome....Plug on the side of the trans case above the removed filter...Clutch linkages adjusted wrong...The top 6 inches should feel like you're moving nothing until you flip up the pedal stop...Then you will feel the engine clutch.. Worn roll pins and groove pins in the clutch linkage cross shaft..

 

[310farmer]

Thanks for the great advice. I found the relief valve. With the plug removed, I can move it back and forth with the tips of my pinky fingers but just barely. It's border line on hanging up. I assume it should glide smoothly in it's housing? After removing it I notice there appears to be another spool type valve inside this main one captured by two small roll pins and spring loaded. It seems to move back and forth just fine with the aid of a small screw driver.
When installing the valve back in the housing does it need to be biased one way or the other? That is all the way in until it bottoms or towards the outside?
I have the manual and it explains the clutch adjust procedure. I'll be checking that next.

 

[310farmer]

Update: The pump is back together and is working good. I'm still chasing the slow movement problem when making multiple moves though. I've checked the relief valve, readjusted the clutch (only off a half turn). Yesterday I removed the return line from the backhoe control valve bank (per the tech manual) and started the engine. Huge gusher of oil trying to return to sump! Strickly a guess, but maybe 3-5 gallons a minute. Seems I have a problem in my control valves. Before I tear into those 6 valves, is there something else I should check to narrow down which valve may be at fault, or is it likely the whole set is just worn out and they are all leaking some?