Does the 'clanking' still occur when the tractor is off? As in lift and lower the 3ph lever with the tractor off. If it clanks then, the linkage that controls the flow may be disturbed. When you move the 3ph does it give resistance? Check to make sure all linkage is hooked up properly.
One of the most common things might be that the flow valve is tightened to far. It may make the 3ph move so slow that you think it's not moving at all. Try moving it to see if it makes any difference.
Maybe some pictures of the switch as well. I looked to see if I had any pictures of mine, but I don't and my tractor has made it's journey to the cabin so I won't be able to give you a reference picture for a while. It should be a little grey button that actuates maybe a quarter inch. If for any reason it's faulty it will not allow the 3ph to move. It is good it's there because an accidental jerk of the 3ph may bend some steel on the backhoe. Try tripping the switch to see if it is faulty. View attachment 273790 From the JD parts diagram it looks like depending on you MY that you may have a different switch.
Do you plan to put a 3ph on it? I know there's a value to getting something working properly, but if you don't need it, then don't worry about it. Is everything else on the tractor working fine? The problem is limited to the 3ph correct? Suggesting it couldn't possibly be an entire hydraulic system problem.
/ Deere 110 TLB 3pt hitch.. not working. Do I need to do something?
