Hyster forklift need more lift power

[laurencen]

hi all, well my Hyster forklift has been doing some work but having a issue lifting what it should, it has no issues lifting 2000 pounds but 3500 it just sits there, tilt will give lift but not the normal lift I need for loading a truck.

when it stalls out it does not bog the motor any unlike the tilt, it just lifts and stops under load, I have tried dealer but unable to get a serial number they offer nothing, my guess is a relief valve somewhere is bleeding the pressure, my old Nissan will be close to lifting the rear end when it stalls the mast.

here is a picture of machine, believe its a H50 the parts diagram has a valve showing a relief valve on front but my valve is nothing like it, anyone have a similar machine and possibly know where the valve is located, maybe its not on the valve to begin with

 

[scootr]

That is a nice looking machine. The service manual is (online PDF) here > Hyster h50 xm (h177) forklift service repair manual

Have you changed the hydraulic filter ?
I had an older Toyota dually, replaced it with a CAT when I wanted an automatic trans and side shift. But still miss the duals at times.

 

[laurencen]

hi scootr, yes all filters were replaced, like I mentioned if you move the tilt to full travel its close to stalling the motor but lift it just reaches travel or with 3500 pounds and sits there no motor loading, its a pressure thing, just not able to locate where the check valve is, manual shows one relief valve on the first block but my block looks nothing like the diagram

one thought was to tee in a pressure gauge and see what actual pressure I get at the cylinder

 

[Harry in Ky]

The H50 should be capable of lifting 5000 Lbs. A pressure gauge is a logical next step. Without it you're pretty much lost as to what's going on. If possible (and it might not be simple) you would like to put it between the pump and the control valve so you can see the difference between readings on lift and tilt circuits separately. Are you sure the lever linkage is opening the lift spool full stroke?

 

[laurencen]

hi Harry, pretty sure its full stroke, the line from pump to valve is metal so not much to tap into the valve is full and packed around it but agree it would be nice to see the pressure between both

the machine is holding easily 4500 pounds I can lift the mast tight and then pull tilt and the weight will come off ground, it holds it for a hour no drop so seals are good

 

[Harry in Ky]

Assuming the relief valve is working because it comes into play on the tilt circuit right? I think you could deadhead either the lift or tilt circuit into a gauge without fear.

I can't think of anything valve related that would cause this problem on only one circuit, but it seems like there must be. What I see in the photo indicates it's only a two spool valve with no provision for a side shift, right?

 

[laurencen]

correct Harry 2 spool, the mast is 3 stage its not original, there is a cylinder at the front maybe 20 inch stroke lifts the forks to 4 feet off ground then another cylinder that lifts the remaining height around 11 foot, both cylinders are on the same hose so the larger cylinder is moving first until it reaches full stroke

looked all around the valves and see no relief valve, where the diagram shows it there is a steel line going somewhere around the front to a block with many hoses, 2 go to the tilt, 2 seem to go into the drive reverse pedal/transmission.

for now I am going to leave as is, if during winter I have some time I will try to attach a gauge and see what gives, its possible the change of mast/cylinder is not upto the job of 5000 pounds looks to have a ram close to 2 inches

 

[ruffdog]

Maybe one of the lift cylinders bleeding by?

 

[Harry in Ky]

Single acting cylinders. Anything "bleeding by" will show up as leak with oil all over the ground.

There is a system relief somewhere, even if it's not in the two spool valve body. It's not the problem because the the tilt function works. A mismatched cylinder doesn't make much sense either. If the cylinder were too small for the load, pressure should still build until the relief opens. If that doesn't happen, you're back to insufficient supply/pressure in the lift circuit for whatever reason.

 

[laurencen]

so played a bit with it, tilt eithey way loads the motor hard when it reaches full travel, lift does load it but not enough to slow the motor, no leaks it will holt weight in air no issues.

there are 2 cylinders for mast a larger short one that lifts forks on first stage to about 4 foot then a smaller cylinder continues the other 2 stages to full height

there is definatly a relief you can hear it release when cylinder reaches end of stroke, will start looking and feeling around when this happens once I get a helper, this has single lever for tilt and lift, for lift move fully left then up and down, its a bit finicky and tends to miss the left pattern