It sounds like a control valve issue. I'd install a manual shut off valve in the supply line to the hoist cyl's, open the valve, raise the cyl's & shut the valve. If the creep is gone the control valve is by-passing.
I checked the forklift and when the mast is up all the way the upper stage on the outer cylinders will creep down first then the center cylinder. So both cylinders are drifting down.
well the thing about freelift systems is the center cylinder will extend first, then when it bottoms out the outer cylinders will start extending.
So if this is what you have when it is raised up to the point of the channels extending the center cylinder will have to completely collapse before the outers will start to drift down IF there is any problems with either of them.
as for the ticking sound that is just packing vibrating against the ram when it gives and drops, that is normal.
One way to isolate the center cylinder away from the other part of the system is to get a gate valve and install it in the main line going from the outer to the center and raise it up... shut off the valve and see if the center stops dropping.
If it stops then the problem is in the center cylinder, if the outer cylinders then start to drop after shutting off that valve then you know the problem is in the outer cylinder safety valve or check valve in control valve.
If I can remember from the last time I had it up on the other cylinders, I think it only came down on the big cylinder. The second stage stayed up. When it creeps down it is not a steady drift down. It does little drops at about every second in a row. When it is doing this it makes a ticking sound with every movement. Hope this answers your questions.
yes it is
so you're saying no matter where you lift it to the mast will drift down all the way to the ground?
how fast is this drift anyway?
It is the large cylinder in the middle. I have replaced the seals in the cylinder but not the small check ball and spring in the bottom of the ram. The ball and spring was moving free and did not have any trash that I could see in it. This has a three cylinder set up. It will creep down even with mast extended up using the other cylinders, but it is the center cylinder that will creep down. Is that small ball in the bottom of ram the saftey valve you are talking about?
typically bad ram packing would be the cause (on older units)
or
a faulty safety valve in one of the cylinder rams(typically on newer units with fluid displacement type systems, rams with no packing)
rare but possibly a bad spool in the control valve
can you be more descriptive as to what type of mast this truck has and the symptoms?
2 or 3 cylinder setup? (duplex v/s triplex mast)
is it the forks only when in freelift without mast channels extended?
or does it do this when mast is up high with channels extended?
if it does this with just forks and carriage only then it is most likely a safety valve in the center cylinder.
If it does this when the channels are extended and the forks drift all the way down and then the channels start to fall too then it is probably a safety valve in one of the outer cylinders