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What happens when Forklift is loaded over rated weight capacity?

Cannonmn

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Jun 25, 2016
I'm guessing some here have had occasion to overload a forklift. I was tempted to take that shortcut since a hotshot trailer is coming with a 6900 lb. item and our Hyster S60XM has a 6000 lb. /24" l.c. Limit. Tailgate is 33" off ground. If I put slings on the forks at the base of the forks to minimize "load center" what do you predict would happen when we suddenly put the 6900 lb. load on the rear of the forks (no lifting, just hold briefly then lower the forks.) I'm thinking the relief valve would open and dump all fluid back to sump, but I don't know how fast the load would drop.

In actuality we've got a rollback wrecker on call so we can get the 6900 lb. Load off safely, but I'd like to know what you predict would happen in case some day we'd have to overload a forklift in an emergency.
 
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Normally what happens is the rear wheels leave the ground. However, this happens when significantly overloaded. Our 8000 lb. forklift will pick up 13,000 lbs. DAMHIK.

Michael
 
seen more than one old forklift with steel added to the counter weight by welded or hung on by chain or the non OSHA way one or 2 guys sitting or standing on the counter weight ken
 
Have the 4 heaviest dudes in the shop sit on the back as counterweights, then you should be fine. You are probably within the margin of error on capacity like the other poster said rear wheels getting air would be the risk.
 
I'm guessing some here have had occasion to overload a forklift. I was tempted to take that shortcut since a hotshot trailer is coming with a 6900 lb. item and our Hyster S60XM has a 6000 lb. /24" l.c. Limit. Tailgate is 33" off ground. If I put slings on the forks at the base of the forks to minimize "load center" what do you predict would happen when we suddenly put the 6900 lb. load on the rear of the forks (no lifting, just hold briefly then lower the forks.) I'm thinking the relief valve would open and dump all fluid back to sump, but I don't know how fast the load would drop.

In actuality we've got a rollback wrecker on call so we can get the 6900 lb. Load off safely, but I'd like to know what you predict would happen in case some day we'd have to overload a forklift in an emergency.
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usually if load in the air the rear wheels come up and it can be quite sudden if load many feet in the air
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then operator lowers load fast then rear wheels come back down fast and you get whip lash. they dont put springs or shock absorbers in fork trucks. if you pick load but still touching floor you often can drag the load
 
Thanks, very interesting and unexpected info, so I could have set that all up easily and will look at doing it in that emergency I envisioned. I never thought about wheels leaving ground but given my sometimes practice of draping straps or wire rope slings across forks which I fully expect to remain level, with nothing to keep them from slipping off the end, I will have to have stops attached if there's a chance of forks tilting forward.
 
Maybe someone knows of a forklift plumbed differently, but I don't know of any with a relief valve between the load and the cylinder. The relief valve is between the pump and the valve. You don't have to worry about a relief valve dumping the load.

You must have a very heavy, compact load to be able to sling it without hitting the mast.

The typical way of picking a overweight load is to pick as much as possible with the mast, and then lift with the tilt cylinders. Every forklift I've seen will curl much more than it will pick when lifting at a close load center. What you have to watch in the situation I described is tipping when lowering the load. The mast is tilted back, so the higher the load the less leverage it has on the counterweight. When you lower the load the angle of the mast gives the load increasing leverage against the counterweight and may start to tip the forklift. To avoid tipping, crib the bottom of the mast while the load is still on the trailer. Make sure the cribbing clears the fork carriage so the load can be completely lowered. When the load has been picked, have the trailer pull out.

While I don't know your forklift or the value or frailness of your load, I'd pick it with no worries.
 
Thanks, very interesting and unexpected info, so I could have set that all up easily and will look at doing it in that emergency I envisioned. I never thought about wheels leaving ground but given my sometimes practice of draping straps or wire rope slings across forks which I fully expect to remain level, with nothing to keep them from slipping off the end, I will have to have stops attached if there's a chance of forks tilting forward.

You really need to spend some time watching YouTube videos of idiots on fork lifts. I usually use some Kant Twists to
keep the sling from moving, even if it is something light.
 
Maybe someone knows of a forklift plumbed differently, but I don't know of any with a relief valve between the load and the cylinder. The relief valve is between the pump and the valve. You don't have to worry about a relief valve dumping the load.

You must have a very heavy, compact load to be able to sling it without hitting the mast.

The typical way of picking a overweight load is to pick as much as possible with the mast, and then lift with the tilt cylinders. Every forklift I've seen will curl much more than it will pick when lifting at a close load center. What you have to watch in the situation I described is tipping when lowering the load. The mast is tilted back, so the higher the load the less leverage it has on the counterweight. When you lower the load the angle of the mast gives the load increasing leverage against the counterweight and may start to tip the forklift. To avoid tipping, crib the bottom of the mast while the load is still on the trailer. Make sure the cribbing clears the fork carriage so the load can be completely lowered. When the load has been picked, have the trailer pull out.

While I don't know your forklift or the value or frailness of your load, I'd pick it with no worries.

I would add, try to raise the load off the trailer a few inches and see what happens to the fork lift. If it lifts and the back tires don't lift then you can do as gbent says to drive out the trailer and let it down super slow. When I used to do that I would practice with the fork lift unloaded away from the trailer so your operator can practice letting it down slow. I used to use two hands sometimes to limit how much force to apply. I once heard the fork lifts have a 10% safety factor built into the weight they say it will lift.

I have also seen Millwrights drive a truck up behind their fork lift and chain them together, also have stood with a few guys on the back as suggested...lol...not the OSHA approved method, but it worked.
 
From a post above: "You must have a heavy, compact load..."

Looks like I only get half-credit there, since this load isn't what I'd call "compact." I don't even know where the lift points, if any, are. Guess I won't cancel the rollback just yet. Come to think of it, there doesn't seem to be any way I'd even get this close enough to my forklift to avoid putting a bad strain on the mast components by exceeding the "load center" specs. What was I thinking???

clark.jpg
 
Various extra counterweight schemes-

yang2.jpg


This is my CAT (actually made by Mitsubishi) 15,500 lb forklift picking up a VMC that weighted about that but the center was more like 40" out thus requiring a chip bin loaded with steel plate. The chip bin was put in place with a smaller forklift and then strapped to the protective cage.

hysterfork1.jpg


My Hyster 8000 lb "boxcar special" lift with the 3" steel plate added so neatly that neither I nor the dealer that sold it to me realized it wasn't factory proceedure, until years later when I noticed none of the other Hyster 80's for sale on the web had this extra plate. Have picked up 9,500 lbs on 24" centers with it.

counterweight_029_3E1BA066-CD06-0804-47E61F84EE55994C.jpg


And then there is this.... LOL... not me, but have done almost as hillbilly using an old woodworking machine as counterweight.

FWIW, lots safer to go up with load than down.... in other words, if mast tilted back all the way with load 1" off shop floor and you don't move the forklift or are going slighly uphill with it, your counterbalance ratio will only get better as the load goes up. But unloading from a truck is more risky as that ratio gets worse as the load gets lower.
 
I've heard a forklift salesman unofficially say that a lift has to be able to pick up and drive with 125% of rated load. No idea how correct that is, but it's been in the right ballpark for me.
 
I should add you don't have to worry about a relief value issue but you do need to pay attention to the condition of the hydraulic hoses, especially if the truck is old and left outside all the time. I once lifted an old Baker gasoline forklift 3 stages up just for the heck of it (with no load except the forks) and right at the top a hose broke !! All I could do is sit there and watch the fork carriage slowly sink to Mother Earth as gallons of hydraulic fluid spilled onto the concrete !

But better it happen then than with a load at least.
 
1. What bobw said x5 - and you will find that breaking masts, etc. is rare. in fact it was never discussed in my forklift driving school. having the load slip off, getting the rear wheels up in the air and losing steering, going over sideways off the end of a loading dock, are all much more common.

2. That said, on the OSHA list of "100 fatal accidents" one involved a bulldozer where a hydraulic hose burst, and sprayed oil all over a very hot exhaust, the resulting fire killing the operator. attend to your hoses....

3. OP, your device is an out-rigger reach truck, very handy, but not quite meant for the schemes you speak of, in particular driving the truck away without running over the outriggers may not be possible.
 
So, OP, is the 'load' the Clark Reach/stacker? Or is it the lifting truck?

If it's the load, take the battery out and you'll be fine.

Another key to working at the limits is smooooth operation. So verify that the truck will drop the load slowly and very smoothly, No jerkiness=no 'micro-accelerations' (made-up term) and less likely to lift the rear. Commit to lowering load without stopping. Blocking the base of the mast is a good idea as well.

Chip
 
So, OP, is the 'load' the Clark Reach/stacker? Or is it the lifting truck?

If it's the load, take the battery out and you'll be fine.

Another key to working at the limits is smooooth operation. So verify that the truck will drop the load slowly and very smoothly, No jerkiness=no 'micro-accelerations' (made-up term) and less likely to lift the rear. Commit to lowering load without stopping. Blocking the base of the mast is a good idea as well.

Chip

Clark green thing is the load. It'll be over rear axle of a 6-wheel trailer, bed height I'm told is 33".

Since the rollback has agreed to be here and only charge $125. For the job, I'm gonna let him unload it, helping as needed. I'll wait till I have a more manageable overload to practice on. Thought about removing the 2400 lb. battery but never having removed a battery that large, I shelved that too. Have visions of my wrench welding itself to the battery compartment and frying my hand. I'm positive I could do it but have a gut feeling it would take hours.
 
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Get good jackstands with wood to spread the load over blacktop, or stack wood cribbing to support the rear of the trailer. Bring load to rear of trailer. Pick it up with the battery-end of the load next to the lifting truck's mast, maybe diagonally to get CG close as possible to mast. Oak or plywood between load and forks to prevent sliding... steel-on-steel is slick. Chain load to mast midway up the load, so it can neither tip or sneak out the bottom if things tip. Place additional 'safety' cribbing stacked right up to just underneath trailer. Purpose of safety cribbing is to catch the load from tipping forward once trailer is gone. Properly placed, fork tips should only be able to drop about 6-8", if things go south. Chain will keep load on forks, and further dropping of forks should level tipped forklift. Pull cribbing out with ropes (by helpers) as you drop successfully, but let them know you won't be stopping so they'll need to be quick about it. Your goal, however, is for none of this tipping to happen.

Even though it's a 'pain', I would still consider removing battery before the lift, so you're comfortably within limits. You can still bring it to the back of the trailer to do that (with the jackstands/cribbing) with the forklift. Take that opportunity to clean/paint the battery compartment if needed...

Good luck and stay safe.
Chip

On edit: I think we were cross-editing... Rollback should be fine, as the Clark weighs about the same as a Suburban, so all the kit is rated for those kinds of loads. An issue to watch is the 'departure angle' between ramp deck and ground. Clark could get 'tippy' if it's basically a three-wheeled thing. Maybe your forklift can play stabilizer on cage of Clark, with either forks or straps.
 
There's more to it than just balancing the truck. Adding counterweights/fat guys is all fun and games, but it doesn't make the lift chains any stronger.

If the chains cut loose that load is coming down, and nothing is going to stop it.
 
Funny this should come up today. I was watching Junkyard Empire on TV last night. They were lifting a big diesel and tranmission and there was "reality TV drama" as the lifted what was beyond the rated capacity of their fork lift, with constant shots of the rising pressure gauge. Needless to say, it held.

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