OK... to give you some back story... I have a personal use Ford F350 Dump... this is our second year of ownership and we have had this problem for the whole time... Well today we dumped a load of crusher run on the driveway and went to lower and of course as normal its not lowering... my buddy and I have only basic knowledge but are both fairly decent mechanically so we went to town on the thing... The problem is only happening from full height till the bottom rails are about 6" above the cab... then it drops decently. We checked all the zirts and greased the bed at different altitudes, we pulled apart the wiring and redid all connections, we took apart the magnetic coil and flow control and tested them and cleaned them up... we are getting a decent click when we hit the button but no drop... so last thing we did was break the hose loose slowly to see if we could bleed down the bed slowly... and we got zero movement until we gave it a pull with a come-along... any help would be greatly appreciated... its not life or death but it would be fantastic to be able to use this thing without having to come-along it down...
The only thing similar I've run into is little short dump beds about 8' or so going up high enough to get over balanced, or for a scissor type stabilizer to over center. Do you still have this problem if you go about 3/4 of the way up, not all the way?
Yeah the problem is definately not any over extension... I get the problem from full height (about 75 degrees) all the way down to just above the cab (> 45 degrees)
Ok, can you post a pic of it while it is up so we can see what kind of hoist it has? If it is a scissor, maybe it has a bent shaft. I guess a slight dent in the cylinder could do this with any type of hoist. Post some pics let us kick ideas around some. I wish you were close cause things like this hold my interest until I get an answer. Mitch
I also forgot to mention... the reservour doesnt appear to be over full... but at some points lifting I get blow-by out of the cap of the reservour even though it isnt even remotely near the top... very strange collateral issue...
hum... id try to isolate my problem to either a cylinder issue or a valve issue. might be able to disconnect the hoses from the valves while the bed is supported by a loader, crane, excavator or something and see if the cylinder will collapse completely on its own. be carefull and be sure to double protect yourself when working under the bed, aka along with the excavator holding it up, have a block back at the hinge, the prop folded down or something else holding so one thing cant fail and squish you. Also lower the body very slowly or you will just have a torrent of oil.
If the rod is bent it will do this
He said in his original post that he had taken the hose loose and it still didn't come down, so it about has to be the cylinder or the hoist, if it isn't a direct lift. A bent cylinder rod does sound like a good possibility.
Thought I would chime in as I'm the friend that helped diagnose the issue. My final thoughts were something being bent due to the way it drops at first, from full up position, but then binds and stops, then we use the come a long to get it down a couple feet then it starts to finish the descend on its own while increasing speed. It is a scissor style hoist and we greased everything with a fitting from multiple positions of the bed to ensure adequate lube. We sprayed a few joints that were not equipped with a fitting with PBS Blaster in case they were the cause. But what gets me is the fluid draining from the reservoir cap/dipstick. I think it leaks most when it's down low, low enough where you can't watch it happen. One question we had was what position should the boom be in to properly check the fluid?
Be careful about being under the bed when its up especially if you have removed the hyd lines.
I had something similar with front mount cycle of dumptrailer. The cylinder had rust/pitted so it would catch or bind. What does the crome finish look like on piston? But I am also confused. About reserivor tank overflowing. I normal check fluid level with cylinders fully closed.
The chrome appears in A-1 condition. The pump and res are located behind the cab on the frame. We cant get to it with the cylinder closed/bed down. I wonder if its overfull all the way down? Is that a reason a cylinder would not descend? Is there a chance the reservoir is pressurizing? Although doesn't explain why cracking the pressure line didn't let it just come right down though. Fluid did gush from the line as we forced it down though.
If you have opened the hydraulic line enough to force oil out when pulling it down, that means there is no way this is a hydraulic issue. It could be a mechanical issue with the hydraulic cylinder, or with another part, but it is not a hydraulic problem. As far as the oil gushing out when you lower it, that is probably because you are over filling it. This will not cause this problem because the excess oil will just be forced out the vent. Sometimes if you can't fill a system w/ the bed down there will be a check plug on the [/U]reservoir, sometimes there isn't. As long as you have enough oil for the cylinder to extend all the way, you have enough oil. I can't stress enough, be very careful around a raised dump bed, they have killed and maimed many an experienced truck mechanic!
Ditto I can't stress enough, be very careful around a raised dump bed, they have killed and maimed many an experienced truck mechanic! Most of these are a one way cylinder , which means they have only one hose . Somewhere there is a vent to let air on the non pressurized side . moisture can get in and rust the upper part of the barrel
This does have a hose connected to the top of the barrel down to the tank. We have noticed the fluid pump into the res tank upon raising it. It could be over filled but despite the tank being white plastic, its too hard to see through so we cant do a visual when the bed is down.
OK, so the problem is not hydraulic, that's good. If you can force it down with a come along, which isn't really a lot of force, don't get me wrong there is some leverage there, but not like pushing it down with a 20 ton hoe. I would look two places, a rusty clinder bore like tiny suggested, is a very real possibility casue its common to leave a bed propped up 6" or so to let water drain, and if it sat for some amount of time it could create a rust line. Next possibility is in the linkage that tips the bed, I have seen and help repair on a chip dump bed that had a scissor hoist, where two verticle plates had rust build between them and swell, binding the linkage in the fully closed position only. If its that you could see definite rub marks and other signs of mechanical problems. Same if the frame had been tweaked in the truck. The hose on the non pressure side of the cylinder doesn't have sufficient size to let you get a plumbers inspection camera in there does it?
I dont know the hose is that big but that's not something we have access to anyhow. As for a rust line, I think that's out also. A rust line at 6" up would not effect the bed getting stalled out when it's 2/3rds fully extended like it does. Linkage is still a possibility however it would have to be an issue at the joint itself as we see zero signs of any parts rubbing. I suspect two possibilities at this point. One would be a bent piston getting bound up as it lowers past the bent point. Or two, a bent pivot point. But my question would be, how far out of straight would the piston have to get in order to make it not slide with the bed weight on it? FYI, the come a long is set up in double leverage mode and it takes a moderate yank on the lever to get it moving each time. It has to lower nearly 2 or more feet before it gets easier and eventually descends on its own.
Use the brute force approach, just pick a component and start tearing things apart till you find the "Aha!" moment. Helps if you have something to lift the bed with, after disconnecting the rod end of the cylinder. If the bed goes up and down freely with the cylinder unpinned, the problem is the cylinder.