This is not to use the cyl as a reservior, but rather to let that sealed chamber vent air back and forth to the hyd tank. I believe you will find that the small hose from the upper portion of the lift cyl attaches to the hydraulic tank above the fluid level. Is the oil aerated? Sounds like you are already overfull, or you would not be purging oil.
If the hoses are old enough, it is not uncommon for the inner wall of the pump supply line to seperate from the outer wall and collapse under suction. Also, a restriction in pump supply can cause the same noise. How is the upper jacket of the cyl refilled when the forks are lowered? How much difference is there between the outer cylinder tube diameter and diameter of the ram? Is there really a large enough space between them to hold any significant amount of fluid? If pump seal is sucking air you will get a similar growl. Engine is Hercules Flat head 6, we've killed a lot of forklifts in 20 years, this ole girl just keeps chuggin away.
Its about 1950's Clark, was told its a HUT8 model when I purchased it 20 years ago, guys at Clark get glassy eyed when I ask for parts or technical info. Post added at 11:28 PM - Previous post was at 11:25 PM. I'm kinda tempted to just manually fill the reservoir side of the lift cylinder, then try it again:shrug. Pretty sure pump is not getting the fluid it needs, its a pretty basic system, 2 control levers on 1 block, a pump, and 2 tilt rams 1 lift ram. Finally disconnected hose from top of cylinder, no hydraulic fluid was flowing into low pressure/reservoir side of the lift ram when lowering forks. Went to lower forks and fluid starts purging out the fill port when forks got down to about 4 feet. So I poured in 5 gallons of fluid (forks were about 5 feet up), ran the forks up a few more feet, pump still growling when hydraulics engaged. The low pressure side of the lift cylinder is also used as the reservoir for the hydraulic system, my first assumption was that it just needed fluid. Raised forks a few feet and started noticing the ram was bone dry and starting to rust. Fired it up this evening and noticed hydraulic pump was growling, there is no dipstick or sight gauge, you just fill till you can see fluid in the fill port. I've never found a manual for this old beast, and not real sure of the model#, Clark has never been able to figure it out by the serial#, so repairs are always exploratory missions. Hi guys, I'm back at the shop in Texas and found a major problem on my old Clark forklift this evening.
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