Weak Ford Backhoe

Oldyellowtractor · Jan 24, 2018

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 · Jan 24, 2018

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 · Jan 24, 2018

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 · Jan 25, 2018

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

oldnslo · Jan 25, 2018

SethBagwell said:
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 · Jan 25, 2018

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 · Jan 25, 2018

ovrszd said:
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 · Jan 25, 2018

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

oldnslo · Jan 26, 2018

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

ovrszd · Jan 26, 2018

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.

LD1 · Jan 26, 2018

If things are slowing down (with no or little load) when it gets hot....as well as getting weaker.....I also suspect pump.

Worn seals shouldnt slow things down too much with little to no load.

But the cylinders are easy enough to test.

Oldyellowtractor · Jan 26, 2018

The valve was leaking quite a bit when I bought it. I took it apart and replaced the quad rings on the spools. The spools looked good and the bores looked good from what I could see. The swing cylinders leak some, the others just seep a little.

I did put some Lucas booster in the fluid last year, it did seem to slow down the cylinder drips, but it didn稚 change the power. I feel like the fluid is getting hot and thinner so the pump can稚 make pressure.

Would a Prince pump be OK? What do you recommend?

LD1 · Jan 26, 2018

Pumps don't make pressure.....they just move fluid.

Restriction to that flow makes pressure.

If cylinders are leaking.....thinner fluid has less resistance to the flow of oil finding it's way back to tank....thus less pressure.....which means less power.

If the pump is worn out, it will pump less fluid.....making thinks slower. And may have enough internal leakage that a little back pressure causes it to not pump enough fluid to build pressure.

But all that is neither here nor there. Don't even think about a pump without testing cylinders as described in this thread. It's easy and quick to do so. Why do you want to jump the gun and look at an expensive pump when testing cylinders is free

4570Man · Jan 26, 2018

It’s likely a splined shaft pump. I don’t think you can just order a pump and stick it on. If you’re lucky you can find an affordable replacement, but you will have to do your homework.

4570Man · Jan 26, 2018

LD1 said:
Pumps don't make pressure.....they just move fluid.

Restriction to that flow makes pressure.

If cylinders are leaking.....thinner fluid has less resistance to the flow of oil finding it's way back to tank....thus less pressure.....which means less power.

If the pump is worn out, it will pump less fluid.....making thinks slower. And may have enough internal leakage that a little back pressure causes it to not pump enough fluid to build pressure.

But all that is neither here nor there. Don't even think about a pump without testing cylinders as described in this thread. It's easy and quick to do so. Why do you want to jump the gun and look at an expensive pump when testing cylinders is free

How do you test the cylinders without removing the hoses and capping them? The test above doesn’t eliminate the valve is a variable. If you can force the rod back in the cylinder without oil spilling the valve definitely leaks. If you can pull the rod out of the cylinder without oil spilling the valve either leaks or fluid is bypassing the inner seal. The other problem is it sounds like his cylinders leak out the gland seal so you’d be forced to make a guess based on rod movement over fluid spilled.

LD1 · Jan 26, 2018

Oldnslo gave good pointers are testing things out in post #5

If cylinders are leaking....they need fixed.

If valve spool is leaking, that also needs fixed.

A pressure gauge can be put on the system and monitored as the thing heats up and the performance deteriorates.

All things I would do before even talking about a pump replacement.

At the end of the day......we cannot be there with the machine to diagnose. All we know is what is being told.....and asking questions and doing simple tests/checks are all pieces to the puzzle. Need more information for anyone to say with 100% certainty what the issue is. And it could even be a combination of all 3......

4570Man · Jan 26, 2018

I wouldn’t loose sleep over a minor cylinder leak. It would cost more than the backhoe is worth to fix all the hydraulics.

ovrszd · Jan 26, 2018

4570Man said:
I wouldn’t loose sleep over a minor cylinder leak. It would cost more than the backhoe is worth to fix all the hydraulics.

I agree. I've got a 34 year old Ford 555A. I accept some cylinder seepage. I repair what is cost effective.

oldnslo · Jan 26, 2018

SethBagwell said:
Would a Prince pump be OK? What do you recommend?

Seth,
Like 4570 states you will have look at how the pump is mounted, drive shaft style, possibly port size and locations, etc. For a heavy duty industrial application I would rate the Parker-Commercial cast iron gear pump as the best, the aluminum housing pumps would be a second choice for any serious use. No clue what is on the machine today. Our old 5000 Ford had a Dowty brand pump on it but this was also an ag tractor so much less hydraulic use vs industrial.