Need hydraulic control valve help on 70s Ford 4500/750 backhoe

[gkbikers]

Hello all.

This is my first post to Heavy Equipment Forums. I'll appreciate any information, advice or help you can offer.

BACKGROUND:
I have searched this site and a number of others, but have not found specific information. However, I KNOW many others have had the same type of problem that I have, which is basically this: I have an old Ford backhoe and the mono-block control valve bank for the 750 model backhoe is dying. It really leaks, the crowd cylinder continues to fall, and the mono-block leaves a puddle on the ground because the mono-block leaks like a kitchen faucet!

I'm sure y'all get the picture. It is an old early 1970s machine, it has not been maintained, it has been abused terribly and then I bought it about a year ago (stupid novice mistake). I've had all the backhoe hoses replaced, new swing chains installed and I had the crowd cylinder rebuilt (thinking it was bypassing - and it may have been) and now the control valves are leaking. Also, various repairmen have worked on it since I have had it and obviously BEFORE I bought it. Hoses have been swapped on the mono-block to try to make it work better, but nothing has helped.

HELP NEEDED:
At this point, I would like to EITHER have the mono-block repaired OR just buy new control valves. The latter is really where I need some detailed information, advice or help. I am not a mechanic, nor am I familiar with hydraulics. However, it is just intuitive that there MUST be a way to put new control valves on this thing. The one thing, above other things, that has me bumfuzzled in that on the swing lever, there is a linkage connected to the control valve (underneath the floor plate your feet sit one) that seems to function to slow the swing at about 75% of its movement either way. I am just guessing. SO, how do I replace the levers and the control valves, etc. on this thing and make it function the way it should? I can live with either a 4 stick arrangement OR 2 stick (like on an excavator) setup.

There, that is my question! THANKS for any help you can give me!!

 

[jimg984]

valves are sealed with o rings, so there is a chance of repairing them, slowing the swing is normal, can swing more by pushing hard on lever GL

 

[gkbikers]

Thanks jimg984. You're right about the repairs and the swing. When I first tested the swing left to right, I thought there was something wrong with the machine because the boom would only swing about 70 degrees each way. Then, probably more by accident than my understanding, I pressed the lever with a lot more force and, whatchya know, the boom swings all the way left and right! Pretty good safety feature.

Regarding the O-rings and repairing this valve block, have you ever heard of a circumstance where the valve block could not be repaired and if so, why? If it can't be repaired, then what is to be done?

Thanks much!

 

[Delmer]

the valve block can crack, or wear out from debris, rust, etc. The spools can get scratched and rust so they won't seal, or the new seals won't last long.

Usually it's just o rings though, how old do you think that rubber is? the same age as your old hoses were. The o rings can usually be replaced without removing the spools (not sure about a ford). The internal valve action is metal on metal, no seals, just tight tolerances, that would not be repairable. BUT, relief valves could be leaking also, causing your drifting issues.

Pull the bottom cover off one of the spools and take the spring off and pull out the o ring, then get the replacements and do them all, piece of cake. Actually dirty and you'll bust a lot of knuckles getting at the stuff, but that's life.

 

[gkbikers]

Hi Delmer and thanks for your help. You make excellent points. As you say, until I get dirty, I won't know what I've got. Piedmont tractor in Gainesville, GA worked on this thing for months. Their thoughts were that the mono-block was cracked. But, they never did what you suggested.

I know the thing really needs to come completely off to do a proper job of evaluation and possible repair. By asking about replacement, I guess I'm getting a little ahead of myself, but I like to plan for the worst and hope for the best.

If this thing cannot be repaired, what are the chances of success in replacement?

 

[Tinkerer]

Welcome to HEF, gkbikers,
If resealing the the valve bank doesn't help you may need to replace the mono-block as was suggested by the techs at Piedmont Tractor.
They may not have considered resealing the valve bank for that reason.

 

[Delmer]

I know the thing really needs to come completely off to do a proper job of evaluation and possible repair.

Why? the bottom cover on each spool is about 2" diameter typically and held on by two small bolts, take one of those off and investigate the inside until you figure it out. Taking all the hoses off the valve will be more work than replacing the seals.

I have no idea what anybody did to your backhoe, you might not either. I'd suspect that this was not their top priority, and they might not have had their best crack mechanic working on your old backhoe. You want it to work right, you fix it.