Hydraulic dump bed questions Please help.

[Chopper]

I bought a 1995 Ford Superduty F-450 dump truck. 15000 GRW.
It has an electric hydraulic pump.
There are two hoses on the cylinder.
The switch turns on the pump and raises the bed fine.
Flipping the switch the other way lets the bed drop via gravity, the pump does not run with the switch in the down position.
The bed holds its position when you let off the switch.
When the bed is less than about 40 degrees angle it drops downs slowly when I hold the switch down.
When I take the bed past about 40 degrees it does not want to drop.
I took it to the top of its travel and had to use a comealong to pull the bed back down.
There is a hose that runs from pump to the bottom of the cylinder.
There is a second hose that goes from the top of the cylinder to the bottom of the reservoir.
There is a solenoid switch on the pump that the dump switch activates to start the pump.
There is a second solenoid that when the dump switch is in the drop position, the solenoid actuates a valve to drop the bed, but the pump does not run.

Is the piston a single or dual acting cylinder?

With the bed stuck up, I had the switch held in the dump position and put a jumper wire to power the pump as well, the pump ran fine, but the bed did not drop. I thought that maybe the piston was dual acting with the two hoses, but apparently I was wrong.

The guy I bought the truck from had only had the truck for a short while. He thought that the pins and linkage on the dump were just stiff from rust and lack of use and that is why gravity would not drop the bed from its fully open position. I greased all the pins, they do not make any noise when the bed is raised or lowered, so I do not think that lubrication is the problem. Like I said the bed goes up nice and smooth.

Any ideas what I can do to get the bed to drop properly?

An additional question is whether I can use the electric pump to run a log splitter, or is the pump and flow too small?

 

[MJPetersen]

Is the piston a single or dual acting cylinder?
An additional question is whether I can use the electric pump to run a log splitter, or is the pump and flow too small?

The way that I understand these things work is that the cylinder is a two way cylinder but is used as a one way and the top side is used as an additional hyd reservoir. You can tell easily by checking the hose that runs to the top of the cylinder--is it a high pressure hose or low pressure? compare it to the bottom hose which will be high pressure. I have never seen a dump truch that had a power down on the dump--it just is not necessary.

Why it is not coming down on its own I cannot say. I only make this observation that the geometry of the dump means that there is a lot less weight to force the piston down in the higher dump angles. how much force was necessary to pull it down?

It would most assuredly be too slow for a splitter and not have enough duty cycle time.

Mike in Warsaw

 

[Dougster]

Sounds like it is a single acting cylinder system with a rod side vent line routed back to the tank rather than fitted with a breather cap to avoid those tiny oil spills and spots that can eventually happen with a breather. I almost wish I had that nifty little feature on my dump trailer.

On the other hand, that vent line could be pinched or plugged somehow and/or drawing back in just enough hydraulic oil to be slowing down your descent if the bed itself doesn't weigh quite enough to both push out... and pull up... enough hydraulic oil to properly reseat itself.

I would disconnect the vent line from the cylinder, plug the line temporarily and try a little breather cap on the cylinder to see what happens:
Hydraulic Cylinder Breather Cap — 1/2in. Dia. | Breather Caps | Northern Tool + Equipment

Dougster

 

[Chopper]

Thanks for the replys. The two hoses are the same size, but the fact that one of the hoses is routed straight to the tank and the tank has a plastic screw on cap means that it is low pressure.

Things might be a little stiff yet. The fact that it works smooth going up and at less than about 40 degrees coming down makes me think it is a design issue.

The bed is an 8' stake side on a 12' chassis, with an added sleeper box/crew cab. I might take off the sleeper box and extend the bed to 12'.

Thanks again.

 

[RonMar]

Show us some pics... The fact that is goes up smoothly is not really relevant as it was designed to do so under hydraulic power with a load on. Any resistance in the pivots and linkages would easilly be overcome going up, yet might apply enough drag on the way down to overcome the force of gravity on an empty bed. Is this a commercially produced product or someones homemade rig? Improper engineering is possible, but I would think less so on a commercially built dumpbed. Have you cleaned and greased all the pivots?

How big is the resovoir on the hydraulic power unit? How big is the hydraulic cylinder? With a small HPU, the extra capacity of the rod end of the cylinder may be necessary to fully lift the bed. Removing the line may make a mess as that end of the cylinder is probably full of oil which will want to come out as soon as you try and lift the bed. Besides, I think if it was a hydraulic restriction, it would be evident from the start of a lowering cycle, not 40 degrees down.

 

[JimR]

I had one of those on my pickup. It is a one way setup with a vent hose. You probably have a sticking release valve or partially plugged up valve. Put a pan under the hose fitting and break the hose loose. I bet the dump drops right down. Or as mentioned, your tank may be too full and the vent is actually trying to suck fluid into the top end of the piston. But even that would not make it neccessary to use a come along to pull it down.