I've got a 1979 Hyster H40H, LPG model. A few years ago, occasionally, there would be be no hydraulic steering or lift. Turning the steering wheel rapidly would most times trigger something and the steering control would return and at the same time, so would the lift. This problem would eventually get worse and the solution to getting steering and lift, was to loosen the hydraulic hose fitting on the back of the pump and while the engine was running, start turning the steering wheel until what seems to be air bleed from the system as fluid would then start to leak at the fitting as the steering and lift returned. Tighten the fitting and away you go. Sometimes, you'd start the truck and no issues, steering and lift working, other times, no steering or lift.
Someone suggested I check the filter in the tank. I recently had the filter housing completely apart, cleaned the smaller diameter strainer, replaced the filter, "O" rings and gasket and new hydraulic fluid, but same problem exists. Seems like the pump is sucking in air somewhere.
Would appreciate any suggestions as to where to start at trying to diagnose what the problem might be.
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It sounds like you might be experiencing an air intrusion or fluid flow problem in your Hyster H40H hydraulic system. Steering and lifting could be the functions that are most likely to be impaired. Although you have already changed the filter and cleaned the strainer, it might be that the air is entering the system via a loose or damaged fitting, a crack in the suction line, or a failing pump seal. One of the effective ways could be to check all suction lines for any sings of wear or cracks that might allow air in. Also, inspect the hydraulic pump in case of wear or damage, particularly the seals that may sometimes fail and let air in while under load. A careful examination of the hoses, fittings, and seals around the pump, and confirming if the reservoir is not contaminated or overfilled, can contribute to the recognition of the true cause. The fact that the disturbance is sometimes removed by just loosening the hose fitting, might also suggest that there could be a possible blockage in the return line or the relief valve might be faulty. A pressure gauge, if you have it, may be used to test the pump pressure to determine any abnormalities in the hydraulic system's performance.
Turtle,
You need to complete multiple test, first being a pressure test at the steer and hydraulic valve. Steer pressure should be about 1800 psi, lift pressure about 3000 and tilt or aux functions about 2300 to 2500. Replace pump or check replace relief valves. If all pressures are good, check tank for dilution rom air. Should see a lot of bubbles in the tank. Suspect pump has failed or broken metal line at pump. Good luck.
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