Hydraulic Hissing?

I just picked up a 1975 Warner&Swasey 1600LG rough terrain forklift. The side shift cylinder is leaking a little hydraulic fluid externally, and the two tilt cylinders creep forward. So All 3 need to come out and be rebuilt. Even with just sitting still with the wheels straight, there is a constant hiss from the power steering, even when I turn both ways. I can find a position where the hiss will stop, but as soon as you start moving the wheel, there's the hiss. Is the hiss actually cavitation of the fluid? What could this be an indication of? Not sure if it's related to the 3 cylinder issues, but I'm thinking it's not. Thanks, Brad

It has been my experience that Hi-lo trucks take a lot of abuse and are built to last, the one we have at my place of employment hisses too. But who cares. Does the hi-lo work correctly? If you are worried about fluid rushing through the lines then drain some fluid out and see if the oil is foaming. If it super loud then that might be an issue.

To me the hiss sound which also may may also be described as a high pitched whine sound, is from fluid in the power steering setting off the popoff/relief valve(s). I bet it the same sound if you turn the wheel all the way to the left or right and hold it tight.

I don't know what kind of steering valve mechanism or hydraulic system you have in there but typically after turning the wheel and stopping, the fluid should just neutral flow right on through. Something in the steering control (either gears or pistons) may be gummed up with crud or something and/or sticking so it does not release to the neutral flow position.

Sounds like you are headed to a steering valve disassembly, cleaning, and repair.

I might add that it probably isn't cavitation but you can look at the fluid coming into the resevoir to see if a lot of bubbles in the fluid.

If it was pump cavitation, it would do it all the time and not stop.

You could also pull the popoff/relief valves to check for operation. Just about have to do it with a pressure guage. If weak and going off early could be a problem but then you would notice that it steers hard.

If the steering is fine when you use it, then the pump and relief valves are probably oil.

Yeah, I've got to start taking the floor plate off and find out where the steering valves are. I've also got to get those cylinders off and take them to get repaired. Do you know what the valves look like? is it a block of some kind that will be located away from the pump?

I have no idea on that thing where the steering is. Follow the steering wheel and the hydraulic lines.

If you are mechanically inclined, you can get new seals and piston rubbers, a/k/a a kit and repair the cylinders your self. Just have to figure out how to get the end caps off. Since there probably is no local dealer around, you can take the rod loose and then take the rod and cylinder down to a hydraulic shop and find the right seals and orings. Cheaper than letting them rebuild them. If the rod and/or cylinder are pitted so bad, they are tearing up the seals, then it may be cheaper to replace it with a new one from bailleynet.com or surpluscenter.com.

If you start taking valves and such apart to clean them, you will probably by taking it wrapped in a rag in a pan or bucket to a hydraulic place anyway to match new orings. If it was IH, the parts diagram would have a size and number.

bc, since my two mast tilt cylinders creep forward(extended), does that mean there is something wrong internally in the cylinders? Because the pressure isn't balanced on each end (when it's supposed to be neutral)? Or would this issue be elsewhere, like in the control valve?

It's hard to say. I assume by mast tilt cylinders you mean the ones that move the mast top forward and back. About the only thing I can think of that would make them creep forward is the weight of the forks. Try picking something up and see if the forks creep any faster. Also try picking something up and see if the forks creep down any with the weight. (I am guessing it uses a hydraulic cylinder(s) to run the forks)

Leaky piston seals in cylinders could cause the creep. Not likely both would happen to leak the same amount though. It could be a leaky valve or relief valve.

Its a process of elimination. If the other cylinders on there don't creep, then you have narrowed down where the possible leak is. Just trace the lines to where they lead to the valve and then it could be anything else downstream going back to the tank.

Can you tilt the mast backwards and let it sit? Leaky cylinder pistons would allow creep in both directions but the valve may as well.

On the valve, look for any thing that looks like a bolt head or nut on the valve body. Those could be a popoff or check ball assembly. With the engine off, remove those and check for crud under the balls. If one is looking down, be ready to catch a ball and spring in case it has that type in it. I'm just guessing here since I haven't been around a forklift in years by they probably use similar hydraulics as tractors. The orings on them aren't leaking or you would know it but be ready to put new ones on sometime.

Check the valve operation also. I assume you have a 2 way valve. Sometimes the linkage gets bent or broken or out of adjustment and the centering piston doesn't come back to the right position. You can hold it a little past where it stops to see if the creep stops. Bleed any pressure off the system before you start taking it apart.

Post back with what you find out. Pics would help.

Yes, I will. If you want to send me your email, I can make sure to copy you when I do if you're interested. I just received the forklift, but have been trying to get all my ceiling joists in for a pole barn renovation project, but I'll probably start taking the forklift apart on Monday. Would help if I could find a manual, but I missed one on ebay a couple weeks ago, so I'm keeping my eye out for another. They don't come up often. Regards, Brad
PS. My email is linked in each post.