My Bobcat 642 malfunctioned. While operating, the lift arms uncontrollably rose to full extension. The tilt cylinder also extended fully. Both foot controls felt jammed and were unresponsive. At the hydraulic control valve, we noticed that the top spool was protruding more than normal. At the rear, the end cover of this spool had cracked, and one mounting ear was separated from the cover. We disconnected the linkage, and attempted to remove the spool from the rear. It slid about 1 inch, then stopped. It sounded and felt like metal to metal interference. We removed the load check nut, which was intact, and seemed fine. Same result. The spool is stuck. Can anyone offer some insight? Are we missing something, should anything else be removed to release the spool? This is a 3 spool control valve, Bobcat #6586287.
Not having first hand knowledge of that valve but from your description I would be thinking something broke either in the valve itself or some place else in the system and got trash in the valve. Wish I could give you a good answer but might just need to start by removing the valve or lines to it. One other thing would be to pull hydraulic filter and open it up to look for debris in there.
KS, Thank you for the response. With the broken end cap, we were assuming that the trouble started there. However, your suggestion that there could have been a prior issue elsewhere is perfectly logical. I certainly will follow your advice to check the filter. I do think that we will eventually be forced to remove the entire valve and deal with it on a bench.
When a cylinder packing starts to come apart it sends pieces of the packing right into the control valve. If its packing material the valve should be okay once you get it apart. If its metal sometimes you can hone the block and save it
Did both the lift and tilt cylinders extending come from both spools "lifting" out of the valve body? Thinking out loud, what could cause both spools to lift, and also crack the bottom cover? a crack down the center of the valve body that leaked oil into both end caps would jam both spools up and crack the bottom cover. A foreign object jamming the linkage could do the same, but that would be hard to also crack the bottom spool cover. And you'd probably see the damage and object, so I'm assuming this is a hydraulic issue that caused the malfunction. Is there any oil leakage underneath? Usually when a spool won't come out, either there's debris inside, or the valve body is cracked, sorry.