Hydraulics not working proper on 555

[JimFord555]

1979 555 backhoe lost all hydraulics suddenly (if I rev it up I can move the loader up and down slowly tilt the loader and get small movements out of the hoe side to side and bucket curl but can t lift the hoe (machine runs perfect)

Fluid level is good

Checked the tank for a plugged screen or loose baffle restricting fluid

Pulled the pump and went through it video of it sent to to a heavy duty mechanic and it looks all good

Removed disassembled and cleaned hoe and loader system over pressure valves (no broken springs and all the poppets seemed to move freely

Switched the hoe system over pressure valve (2400psi) for the bucket curl over pressure valve (2375psi) and still nothing works

In the back hoe manifolds outlet cover I checked:
-regenerative check valve on the side
-back pressure valve on top
-unload valve on top

These are just visual checks by me and springs and poppets are all in good working order seemingly

Connected the main hydraulic hose coming from pump back to the hoe manifold inlet but left the power beyond port capped and capped the hose that connects the power beyond port to the loader manifold. The hoe worked For a minute then stopped and the machine died. I m thinking there isn t enough return path for the fluid withought the loader manifold connected and I created a bottleneck. Any idea if this is correct or an indication of a problem?

I have a mechanic friend coming over with a flow meter but if the machine runs the loader normal without the hoe connected it makes me think the pump and loader are fine and the hoe manifold is letting fluid bypass somewhere so I can t build enough pressure for anything to work properly.

Any idea of what to check next would be very helpful I ve checked everything I can think of at this point, what in the hoe manifold is capable of bypassing fluid ?

Any low or pressure checks that can help diagnose ?

 

[Sean in PA]

I believe that the flow normally goes from the pump to the backhoe first, so the backhoe control valve has two exit ports, one for power beyond that goes on to power the loader, and the other is a return to the sump for the fluid from the back sides of the cylinders being moved. It sounds like the control valve for the hoe is leaking internally to that return port so not enough flow/pressure is getting to anything else when the backhoe control valve is connected.

 

[JimFord555]

(quoted from post at 12:30:08 08/16/23) I believe that the flow normally goes from the pump to the backhoe first, so the backhoe control valve has two exit ports, one for power beyond that goes on to power the loader, and the other is a return to the sump for the fluid from the back sides of the cylinders being moved. It sounds like the control valve for the hoe is leaking internally to that return port so not enough flow/pressure is getting to anything else when the backhoe control valve is connected.

You are correct, that s how its plumbed. The backhoe manifold intake from the pump is on the right side where the system over pressure valve is and the power beyond (too the loader) and the sump return to tank are on the left outlet end of the manifold with the regenerative check valve, back pressure valve and unload valve

How do I go about finding an internal leak ?
Am I correct in understanding that the "control valve" is system pump pressure and its getting through to the sump line that returns to tank. Could that happen in the middle of the manifold in one of the implement sections or is it limited to the end outlet cap where the sump and power beyond are connected ?

 

[Check Break]

You could bypass the hoe and see if there's a change in you loader function. The backhoe control valve is not fun to remove and repair.

 

[Sean in PA]

With the engine running and all control valve spools centered, simply loosen the return line from the backhoe control valve. No fluid should be coming out of there if the backhoe control valve is not leaking internally. The only time fluid should come out of that port is when you are extending or retracting one of the cylinders on the backhoe. If fluid comes out of there when all spools are centered, then there is an internal leak.

 

[JimFord555]

(quoted from post at 15:00:24 08/16/23)
You could bypass the hoe and see if there's a change in you loader function. The backhoe control valve is not fun to remove and repair.

With the hoe bypassed the loader works normally

 

[Check Break]

(quoted from post at 12:14:42 08/16/23)
... what in the hoe manifold is capable of bypassing fluid ?

She can bleed internally between valve sections. There's no telling all that can happen. I have one that bypasses between the swing valve and extendahoe. When you energize the extendahoe, she swings 3x faster.