My '92 F-350 7.3 12' stake pto dump is giving me some concern. Mostly, I just use it around the farm, but will occasionally take it for a ride to get some fertilizer etc.

When I am finished dumping, I push the red (pto) **** all the way in, and then I lower the body slowly, pushing the black dump **** all the way down. The black dump **** has somewhere around 6 inches of travel (guess), the red pto **** has less than an inch of travel.

When the body gets to the frame, I can hear the hydraulics trying to pull it tight against (or through) the frame, even though my pto button is pushed fully in. To get it to stop making that "hydraulics are in a bind and something is going to break" sound, I have to pull up on the dump **** about an inch, and leave it there.

I'm not a dump truck guy, so this is all pretty new to me. However, it makes me wonder if the pto is failing to disengage. The truck is on our farm about a hundred miles away. I'm posting this question hoping I will be a little smarter when I get to the farm and troubleshoot and fix the problem. IIRC, the brand of dump is Omaha.

I'm thinking maybe there is a problem with the pto cable that causes it to engage/disengege. Does the red **** what operates the pto pull a cable, or is the dump **** the cable, and the red **** really just an electrical switch? I do remember seeing what i think was a green wire that was loose near the tranny in the vicinity of the pto when I was fixing a blown brake line.

I'm hoping you folks can teach me a thing or two about how this system operates so I don't have to figure everything out while on my back in the cold.

Thanks!

 

it sounds like the cable is bad not disengaging the pto. You could probably onhook the cable at the pto and move the lever to see if it will engage and disengage properly

 

It sounds like the PTO cable needs to be adjusted.

 

Thanks 79 and bashby,

The cable you're talking about, is it the one that comes from the dump ****?

If that's the case, I can see that the cable is maybe trying to send the cylinder too far closed - correct?

However, once I push the PTO **** to the off position, shouldn't the pto disengage, and the unit not have any fluid being pumped anymore to force the cylinder closed?

My thinking about how this thing operates is that you could move the dump **** in and out all day long, and without the pump running (pto engaged by pulling the red **** out), the body would just sit there on the frame.

I have experience with hydraulics, but on a submarine, not truck dump bodies. Where's my misunderstanding?

 

you are correct, it wont matter what you do with the black **** if the red was working properly and would disengage. The red **** engages the pump, the black moves a valve to direct oil flow between up, float (bypass) and down. Thats why pulling up on the black **** into float mode let the pump stop straining

 

I am guessing it might be the red **** to engage the PTO... Then my thinking is if that is misadjusted for whatever it would grind.

When you operate either control is there an abnormal amount of resistance?

 

Thanks again guys!

It seems to me that I may have two problems.

The dangling wire (or something else) might be causing pto to stay engaged when the red **** is pushed all the way in. That should be an easy check with a volt/ohm meter.

At the same time, the cable leading from the black **** might be adjusted to push the valve past neutral when the black **** is pushed fully down.

No, they doth seem to feel ok when pulled/pushed on.

I've got to get the pto disengaged, as I'm pretty sure it ain't supposed to be pumping at highway speeds - even if the valve is in bypass. Lots of heat, wear and probably pushing the design rpm of the pump. Also, it wouldn't take much for the valve to shift a little, and start porting fluid to raise the bed. That could make quite a mess.

I'm guessing it takes voltage to an internal electromagnet to engage the pto, and lack of voltage allows an internal spring to disengage it. Is my guess right, or does it work on another principle? I don't remember seeing any air or vacuum lines. Not saying they aren't there, but just that I don't remember seeing any.

If electricity causes the pto to engage, it would seem to me that the dangling wire wouldn't have anything to do with the pto not disengaging. Seems like a loose/missing wire would cause it to stay disengaged?? Wiring circuits aren't my strong point though, so I'm asking for anyone to help me with a little understanding here.........

 

very simple setup. you are just over thinking it.

if it was an electrical setup, there would not be a PTO. electric dump setups run an electric pump, and it is controlled by a switch box that looks like an electric winch controller.


your main problem here is that the PTO control cable is not working properly.

there are 2 things that can cause this . either the cable is bad, or it is improperly adjusted.
to figure out what the problem is, you will need a helper.

with the truck shut off, crawl under it and look at the PTO pump. have your helper pull the dump **** out, then push it back in. this cable will be connected to the pump with the hose going to the piston. watch to see this cable move. this will tell you that this is the wrong cable.

now have the helper pull out and push in the red PTO ****. this will be connected to the PTO drive on the side of the trans. if the cable moves, (and i bet it don't) you will need to adjust it.

disconnect the cable from the PTO drive. move the lever all the way the opposite of what it is now. get up and into the truck, start it up, and try to dump it by pulling the black dump **** out. it should not dump.
this will ensure the PTO is not engaged anymore.

if the cable moves both ways, push it all the way down, and reconnect it to the PTO drive. then make sure the cable housing is clamped. have your helper try to pull the PTO out and then push it back in to turn it off now, and it should work properly.

 

Thank you tjc,

What, Me...........Overthink something?

I was trying to figure out how to apply the quadratic equation to it.

let me see here

-b +/- square root of b squared -ac all divided/2a

Nope, still doesn't work. Can't figure it out that way.

Seriously, you've given me a simple way to understand a simple system. I'll print it out and take it down to the farm later on this week.

Take Care!

 

no problem. i try to put things in simple ways, because i deal with a lot of simpleminded people all day long. when i get technical with some of my mechanics and drivers, they look at me like i am talking martian.