I have a UHO83 digger. When you pull back the lever to lift the main boom it goes up and suddenly stops. When the lever is returned to the neutral position and pulled again the boom moves up again then stops again and so on. One of the track motors does the same. I have more than enough hyd oil in the machine, the slew and dipper arm work fine. The machine has two large hyd pumps. A tech has pulled off one of the pumps took it away and concluded that it was worn but not enough to cause problems. Any ideas Whanau.
Preliminary questions; Does the problem occur at all engine RPMs? Does it happen if you 'feather' the control and/or give it full boom up? Not too familliar with the specific machine. Do you know if it has pilot controls or not? I remember working on an old Hitachi many moons ago and it had direct controls with a sort of cam arrangement on the control rods to upstroke the pumps.
Cmark triggered a flashback, yes the old Hitachi's has some spindly little rods that stroked up the pumps, check if your machine has them and that they are returning to zero when all controls are in neutral and whenever any control is moved that they move the pump stroke control levers. It's easy to accidentally bend those silly rods when servicing or repairing the machine.
I had a similar problem on an A series pump. Problem ended up being a gouge in port plate, when pump stroked and pressure rose the oil in gouge would separate the plate from the cylinder block by passing flow/pressure.
I just bought a 2008 Cat 304C CR, going thru the machine and found that when I try to boom up fast the boom stops but if I feather the boom it goes up. I can move the boom any other directing with out issue but when I stop the movement the boom does bounce. No issues with the track motors. So far I have found a leaking hose to the hydraulic oil cooler, the accumulator is hissing. When I bough the machine the hydrualics were extremely low. My plan is to change the hydraulic oil and filters, I have already changed the engine oil. Anyone have an idea what would cause the boom to stop when being pulled up?