I am having trouble with one hydraulic cylinder on my 120 - 2 or 3 First the model and seriel number on the unit say 120-3 however the parts books shows it to be a 120 2 ? The circuit in question is the top cylinder that extends the bucket out or pulls it in, the problem is when the cylinder is just under half way out it will bleed off and fall back down. However if you go past the half way mark all the way out to fully extended it will not bleed off it will hold. The parts book shows a valve assembly on the cylinder that locks it in place However on the unit itself there is no valve only a block for the lines to connect. I went into the spool on this circuit and it appears ok, I then swapped out the two front valves with another circuit that is known to be good. Still no luck. I took a guess that it maybe be in the hand yoke ? Can anyone help me here? Very much appreciated Aaron
There are very few differences between the 120 -2 and the -3. However, one of them is in the control valve. I would suggest you find a -3 manual. Right of the top of my head I don't remember exactly what all is different.
Many issues with 2/3. Therer were two versions of dash 2 known as purple stripe and green strip. Then they renamed the machine a dash 3 after many changes to valve bank and computers. Basically they are all the same machine. If you can post serial number this will identify it. You need to eliminate the bucket cylinder at fault. The way to do this is to deadhead the cylinder ie put cylinder out to fully open position, remove the hose on the return side, start machine and operate the cylinder at pressure side. If you get oil pouring out the return side at cylinder you have a seal bypassing issue. You can confirm this by retracting the cylinder and carry out same procedure with the cylinder in the closed position. If no oil is seen on the return side at the cylinder on both in or out then the next step is to investigate the valve bank. Does the machine have history of any cylinder failure previously???
When you say the top cylinder are you referring to the cylinder no top of the boom or the one on the top of the stick? Is it hooked to linkage that makes the bucket curl and dump? There are lots of reasons the cylinder could be leaking but it sounds like the piston is loose on the rod. When in the middle of the cylinder the rod can move in and out of the piston slightly from the nut being loose. You can possibly check the stick cylinder by putting the stick straight up and down and manually moving it. You would be able to see and feel the slack. The bucket is a little more difficult in that you can't get a pivot point to balance on. The only other problem could be the barrel is swelled in the middle. You and usually check this with a straight edge on the barrel itself. Good Luck!