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Old 08-18-2007, 02:31 PM
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Cavalry Cavalry is offline
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Default Binding hydraulic ram?

My dump truck project has hit a snag. If I lift the box up past the second stage of the ram (telescopic) it does not want to go down. As long as there is weight on it it goes down fine, but as soon as I hit about 35* and the weight transfers to the back pins it will not do down on its own.
The box hinges are pretty crusty but I do not think its binding there. If I leave the down valve open and yank on the box (by hand) it seems to "bounce" a little and then after I work it down to the first stage it goes down fine. When I say "bounce" its like there is air in it or the valve is not open enough to let the fluid out fast.
I know need to check/change the hyd fluid. I am sure its 1985 vintage. The proprod was rusted shut so I did not exactly feel safe hanging out under there.
Someone along the line has cut off the cab overhang. That amount of weight would probably make the box come down on its own. hopefully this is not a design level problem.
My only idea is to strap a few hundred pounds to the front of the bed and work it for awhile with new fluid? Any other ideas?
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Old 08-18-2007, 02:48 PM
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Well you can't go wrong changing the fluid, but it does sound as though something internal is ketching when it goes beyond the first stage. Check all the moving points for the cylinder to be sure there is not a binding point. Most hydraulics I work with are power up and power down and I'm not as familiar with dump trucks. Is this a free fall setup?
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Old 08-18-2007, 06:21 PM
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Quote:
Originally Posted by Cavalry View Post
and the weight transfers to the back pins it will not do down on its own.
The box hinges are pretty crusty but I do not think its binding there.
Sounds like you already know whats going on. I think its weight transfer/center of gravity issues more than ram issues.Why not,instead of just tossing in a couple hundred pounds, rebuild the overhang? Remember the cantilever/leverage effect? Less weight out front doing something is better than more dead weight in the box.

You should check the valve and make sure it is opening all the way.
Could even mount a couple of garage door springs on it to help retract.
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Old 08-18-2007, 06:54 PM
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If the fluid is dirty it may be blocking a check valve. Dirt kill those things.
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Old 08-18-2007, 07:58 PM
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I had that happen with mine. What I found was that the cylinder got tight when it came to the end of the stroke. I fixed it so that a rope would pull the lever on the valve so it would stop before it got that high. Now it comes right down.
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Old 08-18-2007, 08:28 PM
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Any pictures ? Somehow we easier imagine if we see things.
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Last edited by Yadranco; 08-18-2007 at 08:29 PM. Reason: grammar!
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Old 08-18-2007, 09:59 PM
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I have found that a lot of multi stage cylinders begin to leak and this leads to people trying to tighten the seal ring at the top of that stage. And this causes the cylinder to bind on the way down. I see this a lot on the four and five stage cylinders. Adding a couple a hundred pounds for a short time will usualy cure this problem. Although I as others would like to some pics of the bed all the way up and down to the binding point.
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Old 08-18-2007, 11:29 PM
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Quote:
Originally Posted by TommyA View Post
Most hydraulics I work with are power up and power down and I'm not as familiar with dump trucks. Is this a free fall setup?
yes this is a single action ram. power up,gravity down.
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Old 08-18-2007, 11:31 PM
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I fixed it so that a rope would pull the lever on the valve so it would stop before it got that high. Now it comes right down.
The current max height before binding is not enough to dump a sticky load. Most dumps of this size I have come across have a cable or rod that turns off the valve before it gets to the top of the stroke. The cable on this one is broken. It is possible that the ram may have been overextended and slightly bent?
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Old 08-19-2007, 08:16 AM
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Well the more I look at this POS the more I think its the down valve not opening all the way. No matter where on the stroke it is if it freely goes down it goes down slowly.
If I pull it down while both stages are out one will go in while the other goes out. This tells me that the ram is not binding but the fluid just can not get out fast enough.
I got some pics of the complete unit and the pump. The pump is made by monarch hydraulics which appears to still be in business. I will have to get a hold of them for a diagram or something. I have never really messed with these elect/hyd units. I see there is a nut on the side of the pump. It looks like an adjusting nut? Whats that do? If you look at pic 724 its just north of the high pressure hose.
One other thought I have is there is a cable release on the bed. The cable is rotted off near the pump motor. I see no where that this is suppose to hook up? It seems to me that if the emergency down is binding then that might be an issue to check out.
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