Help with my Ford 753 Backhoe, Hydraulic Cylinder/Chain on King Post

I had a problem develop with the 753 Backhoe on my Ford 3400 tractor last fall. I was done using the hoe so I just dropped it for the winter and put a drawbar on the tractor for the winter. I'm getting ready to remount the hoe to do some more digging now and need to fix my problem.

The chain drive on the bottom of the "King Post" of the boom gained a lot of play in it for some reason just as I was finishing up last year. There was not anything that I could see "broken" with the hydraulic cylinders, pistons, or chain. The cylinders are fed via separate hydraulic lines, with a smaller secondary line connected between the two cylinders.

It would seem that I have gotten too much, or not enough, fluid in one cylinder compared to the other, to get their "opposing balance" out of whack creating the slack in the chain. I'm guessing that I need to disconnect one of the ends on the smaller line between the cylinders and place it into a can with some fluid. Then put a piece of tube onto the exposed nipple of the other cylinder and put it into a can (or the same can) with fluid also. (sort of like bleeding brakes). Then, run the hoe and slowly turn the boom to draw in the slack in the chain allowing the cylinders to balance correctly. Hook the line back up between the cylinders and I should be good to go again.

Does this seem correct?

Here is a view of the "tight" side the way that the hoe is sitting on blocks.



Here is a view of the "loose side" showing the amount of slack.



Here is a view of the cylinders connected to the chain. The surprising thing to me is that they are not fastened to the frame but "float" freely in the housing. You could pull back on the left cylinder and take up the slop in the chain around the king post in the photo above. The tight tension on the chain between the two is all that seems to keep the cylinders in place!





Any suggestions as how to proceed?

The Ford 3400 does not have any traction problems once you hang all this ballast off the back end!

 

I think it's unlikely that you're air bound in any way. Best guess from here is there is some wear in a pivot, sprocket wear, chain stretch, or a combo of several.

 

I was thinking more "fluid bound" on one side versus the other, than air in there.

 

Are those double acting cylinders on each side?

 

No, they seem to be "single acting" via the hose connections in the front of the cylinders going to the control box. There is then the smaller secondary line off the rear end of each cylinder that just loops around above and connects to each other.

 

Release the pressure on the "loose" side and push it back in until the slack is out then reconnect. No idea if that would work, but it might.

 

It's possible that one of the piston seals is letting fluid by in one direction and not the other. I do a lot of hydraulic repair work and don't recall a single action cylinder getting bound by either air or fluid, but hey you never know. Was having a discussion with my better half the other day and she said I was right and she was wrong. Whoda thunk it?

 

You'll remember that until the day you die and she's already forgotten about it and will deny it ever happened.

 

Yeah, and probably do that best at that "easy to reach" control box connection versus the front one, or smaller lines between the cylinders. Just crack that connection some till I can get it to drain there. I'll have to check which has the swivel connection.

 

Mark that day on your calendar!

 

And have her initial it.

 

Cracking the line is worth a shot. It defiantly will be cheaper than the alternatives.

 

Doesn't really vent in this setup. The two base ends of the cylinders push the oil back and forth between each other.

 

So are these actually "double acting cylinders" then after all, just plumbed as such to work in balanced opposition to each other? Maybe not since the "inlet" is much bigger than the rear "outlet".

 

Does it still swing equal amounts both directions? Could be letting oil past the spool valve or poppet letting it gradually creep out. My t340 international has the same setup on the Wagner iron works hoe but haven't had this problem I have the manuals for it somewhere I may be able to find a cause in them. I would think these only have force going in as you can't push a chain.

 

I'm not sure about the swing until I get it remounted, but I think so. It comes up against metal stops on the swing before the hydraulics travel ends.

 

Mine hits big rubber blocks but same principal. May even be a spring not centering the valve when you let go of it and slowly letting oil in behind the piston

 

Heavyequipmentforums.com

 

If the two rear ports of the cylinders are just connected to each other by the hose and that hose doesn't connect to any other manifold or valve then they are single acting cylinders.

Got a 20' bat wing brush hog at work with single acting cylinders to raise the wings for transport. The back end of the cylinders just have a vent cap to keep the crud out of them. When the piston seals in the cylinder start to fail the vent will spray oil everywhere. If the seals are good then just some air comes out when you push the lever to open the valve and gravity pulls the deck down.

From wiki:

Single acting vs. double acting
For more details on this topic, see Single- and Double-acting cylinder.

• Single acting cylinders are economical and the simplest design. Hydraulic fluid enters through a port at one end of the cylinder, which extends the rod by means of area difference. An external force or gravity returns the piston rod.

• Double acting cylinders have a port at each end, supplied with hydraulic fluid for both the retraction and extension.