Weak Ford Backhoe

[Oldyellowtractor]

Wondering if someone can point me in the right direction to fix my backhoe.

I have an old Ford 4000 Heavy Industrial 4cyl diesel with a 712 loader and a 723 backhoe. Engine runs great, everything works fine when until it gets hot. When the hydraulic fluid gets hot, the main boom is weak and slow. Really everything is a little weak but it is most noticeable when trying to pick up anything with the boom. It works good for an hour or so, then falls off.

I suspect the pump is worn, but how do I go about knowing for sure? I have never checked hydraulic pressure on anything, and don稚 know how to go about it on this old tractor.

It has new screw on filters and the fluid looks and smells like new.

Thanks

 

[CincyFlyer]

You can check pressure at the port of your valve where the cylinder hoses attach. It's best to tee it in, and reconnect your hose. Check the pressure cold, and watch is as the unit heats up. As the pressure seems to drop as the system heats up, it can easily be a worn pump, or even a worn valve. Make sure you run the cylinder to full extension. You can also put your tee before the valve.

 

[oldnslo]

Main boom weak could also be the seals on the boom cylinder. Will the boom hold a load in position when the load is trying to extend the cylinder? If no this would also point towards worn piston seals

 

[Oldyellowtractor]

So, if the pressure is good, look at the cylinder seals? Or could it be the spool?

 

[oldnslo]

So, if the pressure is good, look at the cylinder seals? Or could it be the spool?

Seth,
Typically spool valves cannot be repaired. They are a metal to metal seal.

A couple of tests you ran to check for cylinder seal leakage.

Place the boom in a position so that the load is trying to extend the cylinder. Center the control valve. Does the cylinder start extending or drifting out? If yes this indicates that you potentially have bad seals in the cylinder.

Place the boom in position so that the load is trying to retract the cylinder. Center the control valve. Does the cylinder start retracting or drifting in? If yes this would point towards an external leak dripping on the ground or leakage past the valve spool.

Depending on how much the seal leak there is you can also either fully extend or fully retract the cylinder and then hold the control so that you are building full pressure to that function. Hold the valve like this for a minute or two and then compare the temperature of the rod end Vs cap end cylinder lines if one is significantly hotter than the other this also indicates bad seals on the cylinder.

 

[ovrszd]

I think your pump is weak. With added heat it loses the ability to create pressure. The main boom cylinder has the most load.

As to "drift". Only way it's the cylinder is if it's spitting fluid out to atmosphere somewhere in the system. If there's no external leak, then drift is caused by a leaking valve.

 

[oldnslo]

As to "drift". Only way it's the cylinder is if it's spitting fluid out to atmosphere somewhere in the system. If there's no external leak, then drift is caused by a leaking valve.

This not a true statement for single rod cylinders. They can and will drift if the load is trying to extend the cylinder without external leakage.

It is true that They will not retract without an external leak.

 

[ovrszd]

If the rod extends there is then more capacity in the system for fluid. Where does it come from?

 

[oldnslo]

Cylinder draws a vacuum and creates a void in the cap end of the cylinder.

 

[ovrszd]

Although I'm not technically smart enough to explain it, it's a fact that the cylinder rod gland seals could be removed and the cylinder would suffer little to no movement under load as long as there are no external leaks in the system.

The only time they are of value is when the valve is activated. When the valve is in it's neutral position, they do nothing.

So a system that drifts under this condition has an external leak or a leaking valve.

Sorry for the subkect drift. I still suspect a weak pump as the cause of the OP's problems.