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Flatbed to dump conversion

Discussion in 'Trucks and Trailers' started by TAF, Jan 27, 2005.

  1. TAF

    TAF LawnSite Member
    from Wa
    Messages: 47

    I have recently removed the flatbed off of my Chev 1 ton dually and am in the process of adding a hydraulic cylinder to turn it into a flatbed dump. I was given a hydraulic cylinder that is 43" long, that fully extends to 73". It has a 4" bore and a 2" rod. It calculates to a bit over 28,000lbs of force. More then enough for the load I wil carry on this truck. I have a new pump etc. With such a long cylinder I have limited options as to how I can mount it. This system will be a "push" type similiar to the type used on dump trailers. Currently I have it mocked into position. How can I calculate the force generated by the mounting geometry I am hoping to use? Fixed end of the cylinder is 10" below the end attached to the bed, which makes the cylinder point up to start pushing up at a 13.5 degree angle. Attachement point on the bed is 30" from the pivot point the bed will pivot on. Bed is 108" long. I have tried to describe this as best I can. After looking at alot of 1 ton dumps I have tried to mimic as best I can with what I have. can anyone help me figure out if this will be adequate? Looking at the geometry on my mini excavators dipper arm there even less of an advantage on boom and dipper cylinder then I have here. I appreciate any help that can be provided.
  2. wroughtn_harv

    wroughtn_harv LawnSite Member
    Messages: 194

    This is interesting.

    What we need you to do is post some pictures. It sounds like it shouldn't be a problem. Probably the most you can legally haul on your one ton after the bed is in place is a ton and a half.

    My biggest concern in your place would be the geomentry being off enough that the load would have to be kept at the back of the bed. That makes for interesting things happening, none of them good, when at speed.

    Yup. We need pictures. You provide pictures we'll give you advice.
  3. TAF

    TAF LawnSite Member
    from Wa
    Messages: 47

    Here is a picture of the geometry that I have mocked up on the truck. This is the best I can do to fit the cylinder in and not have it hitting the stock frame cross member and being right on top of the mufflers. I have used 4, 4" channels under the bed cross ways, which have 2, 4" channels running under them the length of the bed which rest on top of some heavy angles on top of the frame rails. The angles give the length wise channels a flat surface to rest on. Really I do not expect to carry more then 3000lbs on this truck. I did load it with 4200lbs of gravel prior to converting to a dump. Not that I want to push it now. But you can understand why I want a hydraulic dump! I have it all mounted and pulling up the bed with my excavator, it will go a bit beyond 45 degrees. If it will lift 3000lbs, then I am set. The cylinder mounts I have made a overkill so I am not concerned about bending something. Any idea on how to calculate the forces this geometry will create? The DC hydraulic unit is mounted behind the back seat. My local hydraulic guys were not alot of help regarding the geometry question I am asking here. I know I can always change it if needed after the pump is plumbed.

    Attached Files:

    • Geom.bmp
      File size:
      1.4 MB
  4. scott's turf

    scott's turf LawnSite Senior Member
    from NH
    Messages: 949


    I am a mechanical engineer so I think I can help you. From your diagram your hydraulic piston will provide around 6500 lbs of vertical force. This force combined with your piston location will be able to lift 3600 lbs assuming the load is center on your dump. Hope this helps.

  5. work_it

    work_it LawnSite Senior Member
    Messages: 976

    Very interesting post. I've been wondering the same thing lately since I've looked at buying a flatbed. I hope this thread keeps going since it will benifit a lot of us who would not only like to make this type of conversion, but it will also help when others are looking at buying a truck someone else converted.
  6. TAF

    TAF LawnSite Member
    from Wa
    Messages: 47

    Can you provide the method you have used to calculate the force this geometry will lift? Reason being I would like to know if I can change the mount a bit to get more lifting power I will. Not that I want to overload the truck, but I would prefer it to be able of more then I need, rather then less. I am a manufacturing engineer by trade. So I do have an understanding of how geometry changes can affect the ability of this system to lift a load. But I do not know exactly how to calculate the forces that result from a shift in the geometry. As is I could change (lower) the mount on the truck to be 12", rather then the 10" shown on the print. Ideally I would have used a shorter cylinder, but I got 2 of them and the pump in trade for a few hours of work! I could always mount both cylinders but thought it would be overkill. They came off a 7 ton dump trailer. Which figures to be what 2 of them would lift with the 3600lb figure you gave. I do not have measurements of the geometry in that trailer. I think they were mounted at more of angle originally.
  7. Edgewater

    Edgewater LawnSite Senior Member
    Messages: 457

    The way all of our local builders make the beds is with a vertical cylinder at the front. They weld a heavy subframe that sits on the frame of thr truck. Then the fixed end of the cylinder is mounted right behind the cab, centered on the truck. The other end of the cylinder is attached to the cab protector which is usually about 45 inces high. The cab protector has a box in it that just clears the cylinder at the top and gets wider at the bottom so that when the bed is up, it still clears the cylinder as it is now leaning toward the back of the truck.

    Just an idea. If yoy are intersted I may be able to dig up a pic or two
  8. gene gls

    gene gls LawnSite Gold Member
    Messages: 3,213

    If I was to build or get another dump body, it would have the cylinder at the front of the body as Edgewater explains. I have a sissor lift at present that is a dud even thou its rated for a lot more weight than I can carry.

  9. wroughtn_harv

    wroughtn_harv LawnSite Member
    Messages: 194

    Is your lift electric or PTO? And when was the last time you had your cylinder inspected?

    This is a scissor lift I pulled off of a one ton PTO driven. Actually what I did was pull the bed, eight by twelve steel, the lift, and then change everything over to a twelve volt pump.

    The trailer is built for fourteen thousand pounds. I've exceeded that hauling black clay and not had the lift grunt. But I went through heck and three pumps because my hydraulic man said it couldn't be the cylinder. It would climb out of it's skin empty and not budge with about a thousand pounds of load. It turned out to be the cylinder needed repacking. Fixed that and it's a hoss.

  10. scott's turf

    scott's turf LawnSite Senior Member
    from NH
    Messages: 949

    The scissor lift geometry is a little more complex to analize compared to the setup that taf has. Scissor lifts are generally used to maximize the stroke one can obtain by the cylinder.

    Taf, this is how I came up with the 3600 lbs. I don't have access right now to a scanner so I hope you can follow all of this. First look at the triangle with the cylinder. The cylinder is 43" long and is 10" below the dump. So first you need to calculate the perpendicular force which is a ratio comparing cylinder length (hypotenous) and the cylinder force and the 10" dimension. To find that force use the following (cylinder force X dist below the dump)/(cylinder length). (28000 X 10")/(39") This will result in 6511 lbs with the geometry above. Now you have to look at the momentary forces at the bed pivot point. For this assume the weight in the dump bed is centered on the 108" dimension. Use the following formula to calculate the maximum dump load. (dist cylinder from end of dump X perpendicular force)/(half of dump body length). (30" X 6511)/(54") This will result in 3617 lb max lift.

    I hope this has helped you.

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