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Lifting and Loading Pay loaders, Fork lifts, tow motors, jacks and hoists.

Lifting and Loading

Clark Forklift Hydraulic Problem, no flow to cylinder reservoir


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  #1  
Old 01-11-2012, 02:28:42 AM
dalmatiangirl61 dalmatiangirl61 is offline
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Default Clark Forklift Hydraulic Problem, no flow to cylinder reservoir

Hi guys, I'm back at the shop in Texas and found a major problem on my old Clark forklift this evening. 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. 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. Raised forks a few feet and started noticing the ram was bone dry and starting to rust. 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. 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. Went to lower forks and fluid starts purging out the fill port when forks got down to about 4 feet. Finally disconnected hose from top of cylinder, no hydraulic fluid was flowing into low pressure/reservoir side of the lift ram when lowering forks. 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.

I'm kinda tempted to just manually fill the reservoir side of the lift cylinder, then try it again. Any reasons not to do this?

---------- Post added at 11:28 PM ---------- Previous post was at 11:25 PM ----------

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. Engine is Hercules Flat head 6, we've killed a lot of forklifts in 20 years, this ole girl just keeps chuggin away.
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Old 01-11-2012, 03:21:29 AM
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Toesmack Toesmack is offline
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Default Re: Clark Forklift Hydraulic Problem, no flow to cylinder reservoir

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. Also, a restriction in pump supply can cause the same noise. The noise is created by air. Normally a sign of cavation. 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. Is the oil aerated? Sounds like you are already overfull, or you would not be purging oil.

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. 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. That would explain the dry cylinder. If attached below oil level, it would exchange oil in the same fashion, less of a reservior than as a means to lube the upper cyl.

If you fill the upper cyl manually, I think the size of the mess will increase by the amount of oil added.

I'd be lookin' at yer supply line.
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Old 01-11-2012, 01:42:09 PM
ehpower2 ehpower2 is offline
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Default Re: Clark Forklift Hydraulic Problem, no flow to cylinder reservoir

It sounds to me your pump might be needing a rebuild to freshen everything up. i would get a 55 gallon drum and see if oil is coming out of your pumps outlet line and see if it flows as if it doesn't then you have isolated it to either the pump intake line or if there is a tank filter or strainer that might be blocked from sludge. have you ever cleaned the tank out?
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Old 01-11-2012, 01:56:16 PM
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Default Re: Clark Forklift Hydraulic Problem, no flow to cylinder reservoir

Thought about the intake screen, but forgot to say something. Thanks for the reminder!
Rule of thumb on hydraulic oil, if it does not look NEW, change it. It is overdue. Oil level should always be checked with engine off, forks level and on the ground.
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Old 01-11-2012, 03:56:14 PM
dalmatiangirl61 dalmatiangirl61 is offline
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Default Re: Clark Forklift Hydraulic Problem, no flow to cylinder reservoir

No screen that I've ever found. Hydraulic line from top of lift cylinder is plumbed into underside of small reservoir on the machine. Would need to measure to be exact, lift cylinder is 5 or 6 inch diameter, rod is maybe 2.5 to 3 inch, so there is plenty of room for fluid storage. Pump and all cylinders were rebuilt, oh...., 15 years ago, all hoses replaced then too. Pump was a serious pain to pull, I really don't want to do that again.
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Old 01-11-2012, 04:45:52 PM
dalmatiangirl61 dalmatiangirl61 is offline
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Default Re: Clark Forklift Hydraulic Problem, no flow to cylinder reservoir

Engine is Continental flat head, not Herc, it was late. Think I might have found a manual, found a similar lift truck listed as a HUT100 on ebay, looks like mine is a HUT80 Utilitruc.

---------- Post added at 01:45 PM ---------- Previous post was at 01:04 PM ----------

Just went and pulled her out and pulled seat/top cover to trace hydraulic lines. The line from top of lift cylinder is plumbed to underside of upper reservoir (valve is mounted to this), suction line for pump is connected to bottom of much larger lower reservoir. I'm thinking only method of transferring fluid to upper section of the lift cylinder is by vacuum, as the piston lowers it should suck in hydraulic fluid, maybe the top seal is dry and leaking too much air.

Of course that does not explain pump growling, there is plenty of fluid in the reservoir, if there is a screen I'm thinking its on that big bottom fitting for pump suction line, and its NOT going to be easy to get to.
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Old 01-11-2012, 05:27:45 PM
ehpower2 ehpower2 is offline
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Default Re: Clark Forklift Hydraulic Problem, no flow to cylinder reservoir

Hey guys do u think that other tank an acumulator not a tank
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Old 01-11-2012, 05:47:08 PM
A.D. Baker A.D. Baker is offline
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Default Re: Clark Forklift Hydraulic Problem, no flow to cylinder reservoir

Quote:
Originally Posted by dalmatiangirl61 View Post
Engine is Continental flat head, not Herc, it was late. Think I might have found a manual, found a similar lift truck listed as a HUT100 on ebay, looks like mine is a HUT80 Utilitruc.

---------- Post added at 01:45 PM ---------- Previous post was at 01:04 PM ----------

Just went and pulled her out and pulled seat/top cover to trace hydraulic lines. The line from top of lift cylinder is plumbed to underside of upper reservoir (valve is mounted to this), suction line for pump is connected to bottom of much larger lower reservoir. I'm thinking only method of transferring fluid to upper section of the lift cylinder is by vacuum, as the piston lowers it should suck in hydraulic fluid, maybe the top seal is dry and leaking too much air.

Of course that does not explain pump growling, there is plenty of fluid in the reservoir, if there is a screen I'm thinking its on that big bottom fitting for pump suction line, and its NOT going to be easy to get to.
I also say if the pump is making noise that the pump needs rebuilt... But a hose could have collapsed and starving the hydro. pump of oil.. just a thought.
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Old 01-11-2012, 05:55:05 PM
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Default Re: Clark Forklift Hydraulic Problem, no flow to cylinder reservoir

I hear you on tough is it to pull the suction line. I know it also entails draining the tank, but should tell you a lot. Really think you got a serious restriction in the line or the screen. Not uncommon for the screen to be integrated with the outlet fittings. Once the suction line is off, you can pull the lower fitting.

You are correct that suction is how that upper cyl is filled. Bad seal equals suction leak. Would also explain the rust. Rainwater. Is the reservior plumbed into the upper cylinder seperate from the main hydraulic tank? If so, probably not really part of the hyd system, more so just a source of lube for the upper chamber of the cyl.

---------- Post added at 01:55 PM ---------- Previous post was at 01:52 PM ----------

Small tank would not be an accumulator. Not on the pressure side of the system.
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Old 01-11-2012, 06:22:42 PM
dalmatiangirl61 dalmatiangirl61 is offline
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Default Re: Clark Forklift Hydraulic Problem, no flow to cylinder reservoir

In the pic showing valve- hose closest to camera is pressure line to bottom of lift cylinder, 2 smaller hoses go to tilt cylinders, large hose furthest from camera is pressure hose from pump. Valve is bolted to the upper section of reservoir, when lowering forks fluid is dumped into this section (you can hear it), then flows down into lower section of reservoir. Hose to top of lift cylinder is bolted to bottom of the upper reservoir, guess there are some type of baffles to create a pool for this line to suck from.

The lower/larger reservoir is behind the side plate of the machine, oh lord that's got to be 10 gallons or more There is a drain hole, I just don't think I have a 3" high drain pan that big.

Machine is parked inside most of the time, rod is always wet with hydraulic fluid. I think we replaced that suction line when pump was rebuilt, its just been too long to remember.

Thanks guys!
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