dump bed won't dump with load! HELP

Discussion in 'Trucks and Trailers' started by vntgrcr, Mar 26, 2005.

  1. vntgrcr

    vntgrcr LawnSite Senior Member
    Messages: 282

    HI Guys,
    I just purchased a 95 Isuzu with a mason dump body. The dump mechanism is a 12volt electric unit, no PTO. I put a load of dirt/mud on it yesterday of about 5 skid steer buckets, and it wouldn't dump. I had to pull some out before it would go up. It has a Fenner pump on it and goes up and down fine empty. It also has some kind of regulator on the output with a twist knob that says "faster" if you turn it counterclockwise. Can somebody help me diagnose the problem. Do I need a pressure gauge on one of the lines and how much fluid and what kind goes in the resevoir? I am bummed because this thing supposedly could lift 5 ton of stone. At least that is what the previous owner lied to me about!
  2. hosejockey2002

    hosejockey2002 LawnSite Bronze Member
    Messages: 1,195

    First of all, with 5 skid steer buckets of mud you may be overloading the hoist. Does the motor stall, or does it just not lift? If the motor stalls under load, you may have a bad electrical connection or the motor itself may be bad. If it runs, but does not lift, then the pump may be bad or low on fluid. BTW, if this is an NPR, it's WAY overloaded with 5 tons of stone on board. Capacity for this truck should be around half of that.
  3. grass_cuttin_fool

    grass_cuttin_fool LawnSite Gold Member
    Messages: 3,526

    I could be wrong but most 12 volt electric pumps/ hoist are not rated for that much weight, but I havent seen them all so.............. AS for fluid you need to check the owners manual, most take hydraulic fluid but I have known some that took regular motor oil also
  4. gene gls

    gene gls LawnSite Gold Member
    Messages: 3,213

    You over loaded your hoist. I have a Venco hoist rated for 8 ton under my 10' platforme dump. It will only pick up 2 ton because there is not much overhang.

  5. vntgrcr

    vntgrcr LawnSite Senior Member
    Messages: 282

    Thanks for the tips guys. My only reference to electric lifts is a freinds old dump trailer that I have had 4 ton on and lifted no problem. But it sounds like I may have just overloaded it. Thanks for the info and I will be more careful.
  6. Gravel Rat

    Gravel Rat LawnSite Fanatic
    Messages: 9,544

    Thats the problem with scissor hoists is they don't have any power. My old 88 F-450 with a 11.5 box and a telescoping post hoist would dump 8500lbs of gravel with no problems. The hydraulics were PTO so that does make a difference. I think the hoist would bend the frame behind the cab before it ever stalled.

    When is the last time you checked the hydraulic fluid level ?

    I wouldn't class 5 skid steer bucket fulls to be much unless its a yard per bucket which I doubt.

    The pump should put full PSI and GPM to the hoist so there shouldn't be a regulator to adjust the pressure. You may want to go with a PTO and pump set up if you want more reliability and save on batteries.
  7. specialtylc

    specialtylc LawnSite Bronze Member
    Messages: 1,656

    The hoist should have a model number which will tell you what it is rated to lift. I have an Isuzu NPR that I had built with a 12 ton electric hoist on it. And I have had 9000lbs of gravel on it before and it lifted it just fine.
  8. vntgrcr

    vntgrcr LawnSite Senior Member
    Messages: 282

    Can you tell me where that rating might be? I looked around and didn't see anything. The piston on this bed is pretty good size, that is why I was surprised it wouldn't lift it. I did put some fluid in it and will try it again tomorrow and see what happens. Thanks
  9. cet

    cet LawnSite Member
    from Toronto
    Messages: 89

    If you are low on fluid then it would not lift to the max even if it was empty.
  10. StealthDT

    StealthDT LawnSite Member
    Messages: 97

    I might be able to clear up a few things. The valve could be a flow control rather than regulator. We use a check valve flow control to slow down the bed on the downstroke for safety. This way if the bed is loaded, it won't hit the frame so hard. I've seen flow controls without the check valve, which would work in both directions.

    The next thing I noticed was you didn't mention a high pitched squeel coming from the pump under load. This noise is usually associated with the relief valve opening at full pressure. If your pump is worn out, then it will never output the pressure to trigger the relief, it just bypasses at the gears. Most 12VDC dumps have outputs between 2,000 and 2,500 psi. A pressure gauge is handy for troubleshooting.

    When we sell a dump kit, we advise using Dextron 2 transmission fluid in the pump for cold climates. Tractor hydraulic fluid can also be used. For commercial applications in hot climate, use 30 weight motor oil. This increases the life of the pump, but can cause high amp draws in cold weather. So it's a trade-off on what your purpose is....

    Yes, scissor lifts are weakest when closed. Typically they need a larger diameter cylinder for the same capacity of a telescoping cylinder dump. Load the dump bed more to the rear to help it lift. The geometry of the scissor determines the leverage it's cylinder can use to open the mechanism & dump. There is also a great deal of difference between a forward opening and rear opening scissor. A scissor that pivots from pins & mounts as far forward on the truck frame & bed will lift more, but it's dump angle suffers. This type is the more conventional design. If a scissor is mounted to the rear, it dumps less, but the angle is higher. In this case the cylinder diameter is usually increased, and the geometry changed to add leverage.

    Not trying to write a book, but figured I could help. Check the fluid level, pressure, and open flow valve.

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