I’m new to the forum and this is my first forklift. I have worked on old tractors but am finding this quite different. Several weeks ago I purchased an old Clark GPX15 just to use around the shop. I believe it is a 1997 model and had been setting for a few years. I rebuilt the propane system got it running well. I also rebuild the brakes and replaced the wheel bearings. The steering cylinder and the side shift cylinder had large leaks so I resealed them. I took it for a test drive after the cylinder work and it worked great for only about 10 minutes. All of a sudden the hydraulics started acting sluggish and the was a noise like cavitation. I checked the fluid level and it was good. The lift and tilt are very slow. When I turn the steering wheel the steering works and the noise stops. When I stop turning the steering wheel noise starts again. It’s hard to tell where the noise is coming from but it feels like the priority diversion valve is vibrating. I removed the priority diversion valve and cleaned it but found nothing obviously wrong. The pressure on the control valve is only about 200 psi. When the forklift is running and no valves operating, I can see the main return to tank which seems right. I also seen return that is from the steering (steering wheel not turning) and/or relief from the priority diversion valve. Should there be a return when there is no steering motion? I really don’t know where to look next. Any advice would be greatly appropriated.
Sounds as if it had been sitting, you got it going, and accumulated "trash/gum" or whatever was stirred up and has clogged your filter Cheapest/quickest is to get a new filter, zip it up and see what happens. Can compare any pressures you have taken with any you gained.
Thanks for your reply. I replaced the 2 filters I could find. The low pressure on at the return to the tank and a high pressure one near the pump. To my disappointment, there was no change.
Send a pic of the pump, showing it and hoses in and out. As if I were looking down on it.
Thanks for your reply. I am on hunting trip now but returning in few days. I will gladly post a picture of the pump. Thanks
Wishing success on hunt. Standing by.
Here is atop view of my pump. I have removed the orbital valve hoping to find an obvious problem.
Most of my experience was with Clarks up to/thru the C500 era. Some of the GPX of course varies, but hydraulics is still hydraulics. 1. The noise. It is from a level of cavitation due to a suction leak. Check the supply/feed from source to pump intake. Even under the clamps, a crack there can be enough to cause. 2. The noise stops when steered.. Older machines had like a double Vickers pump. Main fed lift/tilt, and secondary fed power steer. So when you were steering, the main segment is idle. But apparently you have a single stage pump with priority valve to sort...? Two things here.. Priority may have "debris" still, tho cleaned, and, somewhere on the pump should be a pressure adjustment "cartridge." Find it, remove and disassemble carefully. Sort of a needle and seat device. Thin shims spacing in it. Do not lose/change any of them. This can get fine steel debris in it and cause varying pressure/chatter? effects. It was working, parked. You revived, and it worked for a short time. You repacked other functions of the hydraulic system. Debris, small ( fine little slivers of steel) enough to go thru the filters will still cause a variance in the pressure setting cartridge. It is either your fluid supply (=cavitation) or the settings of pressure in pump/priority(=constant). This may seem vague or wide ranging due to not seeing/hearing, and not having a hands on. Hope it may lead you to areas of the causes tho.
Thank you for your reply. This is very interesting. I had assumed the pump was working (with no evidence to justify it) but now I should probably rethink this. The pressure adjustment cartridge with debris seems like a possible cause. I will find this cartridge and check it out. Thanks for the help, I didn’t know which direction to go. Thank you.
I drained the hydraulic tank. It looks like the problem is a clogged suction strainer.
Thanks for letting us know what the problem was. I have a friend with a gpx30 that sounds like "cavitation" when any function is used. This thread has given me some ideas to start on. Maybe we will start at number one from above post draining the tank and checking the suction strainer, then clamps, hoses, and new filters.