Towable Backhoe Hydraulics "Soft" and sluggish

[PV Bear]

I have a towable (small) backhoe made by Central Hydraulics (Harbor Freight). Recently the hydraulic operation has slowed and become weaker. I have changed the spin-on filter and checked the oil level and it is OK. The oil appeared clear, but I believe I checked it while the unit was cold so I may have missed any stirred up contamination. It does not appear to have a screen from the outlet of the tank to the suction line of the pump - otherwise I would check that for debris also.
The backhoe is used on a small barge and does dip the arm and one of the cylinders under the water frequently whilw digging. I have also noticed a couple of the cylinder seals are weeping slightly. The seal leaks are very slight, so i did not think that would be the problem, but I have little in the way of hydraulic knowledge, so please let me know if this would cause the problem.
I also noticed an earlier answer to a post suggesting to bleed the cylinders of air. How do I go about doing this? The owners manual just states to fully cycle all cylinders through their range of motion to bleed the system. Thanks for any help you can offer.

 

[J_J]

Cycling the cylinders, should bleed the air if any.

Is the engine running at the same speed as when new?

This is in hindsight, but it would have been a good idea to check the pressure when new, to establish a baseline. You can still add a pressure gage check point before and after the valve to check the pump pressure, relief pressure, etc. Cylinders leaking internally, valve spools leaking, pump not pumping like when new, could be anything. If the cylinders are leaking externally, then it is possible to suck in water at that cylinder. If it has sucked in a lot of water, you would notice the color of the fluid changing to a milky color. It sound like you have a return line filter, so you have to assume that the tank is clean. You might check the quality of the hydraulic tank cap to filter air/moisture, etc. My particular hydraulic system has a filter on the suction side, maybe because it is a closed loop system. Some say that suction filters are dangerous, but whatever.

 

[PV Bear]

How much will the fluid level in the tank affect operation? I checked the level and it is in the acceptable range, but the manufacturer rep noted the oil level as a potential problem. Could part of the problem be that this particular machine needs an very (top of range on dipstick or above) full reservoir to operate properly??? That just seems too simple, but I thought I'd throw it out there. The rep also confirmed that the only filter on the system is the spin on filter which is located on the return line just before entering the tank.
I guess I'll add some more fluid this evening and see if additional fluid will help any. Thanks again for any help or suggestions.

 

[dfkrug]

How much will the fluid level in the tank affect operation? I checked the level and it is in the acceptable range, but the manufacturer rep noted the oil level as a potential problem. Could part of the problem be that this particular machine needs an very (top of range on dipstick or above) full reservoir to operate properly???

Fluid level certainly could be the problem. At full extention of the dipper
and boom, the volume of oil in the cylinders is the greatest, so the
volume in the reservoir is the lowest. One sip of air by the hyd pump and
you get air entrainment, which requires a bit of cylinder cycling to be
removed. Also, is the hoe always level? I know I could starve my CADDigger
pump when the angle got too steep.

 

[J_J]

Try this, extend all the cylinders, and look at the level in the tank. This is the lowest you will get as the push stroke uses the most oil. Your suction line should be close to the bottom. Is the relief circuit activating when at the end of the cylinder stroke? That will tell you that the fluid is at the pressure set on the relief valve. Like I said before, get a gage and test things. Has the fluid level gone down since new?

 

[JoelD]

First blush sounds like the pump may be failing. On my towable, the pump failed, but that resulted in an external leak.

If all cyls are slowing then must be pump in my mind, can't imagine all valves failing the same way at the same time.

I would think remote you've got enough dirt to cause a problem in the system.

As others have posted, check for milky color of oil, if so, would be water in system, not sure what that would do to speed though.

I guess another option would be pump has spun the key on the shaft in your motor mount and maybe pump is not spinning as fast as motor I had that happen to me once.

Joel