Gentlemen good evening! Long time lurker needs some help. My issue; I just picked up a Bobcat 331, s/n 234314211, with just shy of 1900 hours on it. I've had an intermittent issue where the boom cylinder refuses to move. Today it was very stubborn, and after a few starts and some troubleshooting, I was able to get it to raise... but it won't go back down. I have no idea why it decided to at least lift this time, but not before. The first time it did this, I did some searching online and found a post about the pattern changer being between positions. I brought the switch all the way over to ISO and the controls worked fine. This time that simple fix didn't do anything, and I think it might have been coincidence. My troubleshooting; - Engine power level doesn't seem to affect the problem - All other circuits work fine - machine moves fine - when moving the joystick to bring up the boom I didn't hear any fluid moving, or relieving, but this machine's hydraulics are pretty quiet, and I'm not used to it - Switching from ISO to SAE, the problem "switches joysticks." In the ISO configuration the right joystick fails to move the boom, in the SAE configuration the problem moves over to the left joystick. - when the boom cylinder did lift, it wasn't as smooth as the other circuits; there was a lag in the controls. The right joystick seems like it has a stronger "spring return" feeling to center position, than it does on curl/uncurl or left/right movements. What I've done to it; I added a thumb kit to it. The old stick-side flat face quick disconnects were pretty worn and dripping. They just got replaced today. The issue occured prior to thumb kit install, as well. I don't think this is related, unless the air introduced into the lines is somehow causing this problem. Otherwise I've only put about 5 hours on the machine so far, clearing a flat spot in the yard, and picking up a few logs with the thumb. This is my first excavator, so I'm a bit of a novice, but I have worked with tractors for a while. Any assistance would be greatly appreciated. I'll be sure to post the solution for the next guy. My thoughts; - Could the pattern changer have an issue? It's turned all the way over to the contact, and all other inputs work correctly in both patterns. - The issue jumping between joysticks when I do switch the pattern changer makes me think it is something outside of the low pressure hydraulics, and might be the spool or the cylinder, but this is new to me! - What does a jammed spool look/feel like? Would a damaged cylinder do something like this? - After getting home I realized I should have looked to see if the hydraulic lines going to the boom cylinder were "jumping" with the applied pressure when I moved the control stick. If they aren't I can assume the problem is behind them. If they are than I must have a jammed cylinder, right? Like I said above, I didn't hear fluid moving when I made control inputs, but I'm new to this thing. I'm excited to be told to check something completely obvious that I may have missed. Thanks in advance. Hoping this is a cheap fix, haha. -- Aaron
I would check the condition of the boom cylinder and possibly the circuit reliefs of that section..........or the load checks. Since the problem shifted with the pattern changer it is not a pilot system problem. Since your other hydraulics are smoothe, its not a pump issue. A broken centering spring on the main control valve(boom spool) could cause similar issues in a single circuit.
Can you direct me to where the circuit reliefs and load checks are? Would those be in the valve? I attached the parts diagram. I should have mentioned that the boom cylinder is seeping at the wiper seal, as well. I doubt that is the source of the problem, but if you think it's a good idea to check that I might as well get those parts on order too... Aaron
Good day Housebus We can make some information for you however I suggest that you check out this possibility, you have two small lines from the pattern change valve each going to opposite ends of the spool (MainValve) should the be an obstruction in one line it can prevent fluid draining from the opposing side of the spool preventing shifting. Removing those two pilot connections and checking the pilot pressure when you operate the boom R.C.V. will determine if that is where the problem is at. Kind regards Uffex
This may help you follow the explanation, my compliments on your problem presentation. Kind regards Uffex
That would be a external leak which wouldn't cause your issue Circuit reliefs look like #5, load check #8, centering springs are within #2. As said above, you can remove the pilot lines from the boom section and pressure gauge test there at the end of each hose. Boom up will pressurize at one hose, boom down will pressurize the other. You should see pilot system pressure at both hoses (not sure on your model but should be between 300-400 psi on average.) You can remove the 2 bolt caps on your spool ends and the centering springs should be right there under the cap. Make sure one of those isnt broken. DO NOT take anything apart on the valve while the engine is running, and make sure the boom is relaxed safely on the ground.
Uffex - what an awesome resource your website is. Bookmarked! I'll look into the pilot system and pattern change valve's lines; what you describe makes a lot of sense. Vetech - I'll check those springs out, as soon as I can get time to work on the thing. I have a pressure gauge in the mail. I did run the machine briefly today and the problem persists. The lines going to the cylinder don't "lurch" when the joystick is moved, so I think we can rule out any kind of internal failure of the boom cylinder. Will keep you posted! Appreciate the guidance.
Thank you for the kind remarks Stay safe Uffex
This may help some. Kind regards Uffex
I have a similar issue on a new to me 1994 331 no boom up or boom down, but I can get the boom to lift by bottoming out the bucket cylinder and holding full stick on the bucket rcv. I have to very lightly pull back and on boom rcv about 1/2" and I can get the boom to raise, any farther pulling the boom drops. Also pushing the boom rcv forward ever so slightly will raise the boom while holding full pressure on the bucket rcv. Just cracking into this I'll update with my findings. Any input is very much appreciated