Hi I have a cat 312c excavator that the hydraulic cylinder on the sticks stuck in the out position. It acts like a stuck valve but may be the relief valve. I broke the lines loose cylinder returns. Or push it against a tree and can get it to return but returns to the stuck position. Any help would be appreciated.
When you say stuck out do you mean the cylinder is stuck out with the stick stuck in, or the stick is stuck out with the cylinder stuck in? (Good job I'm sober ) If the cylinder is stuck out and won't retract then most likely you've got the piston broken off the end of the rod. If the cylinder is stuck in and won't extend, then pray tell does it go in as soon as you start the engine or only when you raise the safety lever?
It is sticking in as soon as u lift the safety lever
OK. So there's a good chance the problem is in the pilot control valve (which is the component that the joystick attaches to). The first quick and dirty check is to lift the rubber boot around the LH joystick and see if the plunger is stuck down. If all looks OK then you'll need to post your serial number and someone will be along to tell you to swap around a couple of hoses to either confirm or eliminate the pilot control valve as the problem.
My serial number is 01376
Need the prefix of 3 letters prior to the 5-digit S/N to confirm exactly what model of 312C it is. There are a dozen or so options.
Cae01376
OK, so you have a grey market machine originally for the Japanese home market and originally uses Parts Manual reference XEBP7955/XJBP7955. If you want parts for this machine in the US you should use Parts Manual reference SEBP3833 which is for a US-built machine of CBA prefix and a Serial Number higher that CBA01201. I can't add much to Cmark's post above. As a first step see if the plunger that operates the stick out function in the pilot control valve in the cab (if you lift the rubber boot you will find 4 plungers in the valve located at 90 degrees from one another) is stuck down and let us know what you find.
No they are not stuck down. I am getting constant pressure on my cylinder in hydraulic hose side
And now this cylinder is going in as soon as I start the engine with safety lever up
If you put the safety lever down does the movement of the cylinder stop..?
No it does not
OK, well in that case it does not appear as though it's the pilot side of the system that's causing the issue, because if it was then cutting the pilot system would stop the movement. The description that you are using for the cylinder isn't what we normally use - not your fault I hasten to add. Just to make sure we are on the same page when you say it's the "cylinder on the stick" do you mean it's the cylinder mounted on stick that curls the bucket or is it the cylinder mounted on the top of the boom that moves the stick in and out...?
Nige, i hope you get that unstuck and working properly
The $$$$ is multiplying by the minute... Take the cylinder off and apart.... If you probably find major damage in the cylinder you will probably find it in the valve also..... Lots of cleaning ahead
Mike, I was thinking to look inside the main control valve first to see whether or not the spool was jammed by a piece of debris (and what that debris looked like) before recommending opening the cylinder up.
Your experience may be different but usually the debris comes from the components of that circuit?
Often, but not necessarily. That's why I prefer to look in the control valve first to see what's jamming it and what it looks like, then go looking for where it came from armed with that information.
I'm trying to get the spool valve out but no luck. Any tricks
Try tapping from the other direction
There's not an other end it's a dual spool valve body
According to the parts book I'm looking at, there are caps on both ends of each spool. Also be aware that the stick circuit has two control valves and a regen valve, although the regen only operates during stick in.
How do you know which spool to go looking at..? I wasn't aware that we had actually identified which cylinder is causing the problem - see my post #13 on Page 1.
312 cylinder stuck curling I have a similar prob, my 312 cylinder is sticking. I followed the info given in this thread so far. It is the cylinder hooked to the bucket. When I start the machine it automatically curls in, I can curl it back out but when I let off control it curls back in. This is a very slow curl. And when I lift the safety latch that should stop all hydraulic movement it still curls in. Which tells me it is not in the pilot control. Where should I look next. And I have 3 of these machines so I already swapped out the cylinder with another working cylinder and this did nothing. So I eliminate it being a bad cylinder. Thanks for any help
Port relief valves, try swapping them around, mark them so you get them back in the right spots if you're not swapping end for end if you know what I mean.
Yes, where are the port relief valves located. Are they right by hydraulic pump in side door. thanks
In the main control valve, I can't tell you on that machine exactly where. The bucket cylinder spool may have one only, or one for each hose.
The slow curling machine. I'd look to see if the spool centering springs (concentric) are still securely fastened to the spool.
Hello, I had temporally gave up on this machine. I had the cylinder rebuilt last week. When you stop the control of the bucket cylinder it still curls on its own. This is not just gravity, it curls all the way in till it bottoms out. Thank you for all the replies. Out side of this being stuck the machine works great. I am having a hard time figuring out which valve the main spool runs the bucket?
Follow the hydraulic lines from the bucket cylinder back to the MCV.
Sounds like you either are supplying pilot pressure to keep the main spool shifted, or your main spool is sticking. Find your main control section for your stick, remove the pilot lines on each side and plug those lines, that will eliminate your pilot control oil from supplying that circuit. If it quits moving, check your joystick manipulator plungers. If it still moves, you may have something blocking the main spool from centering or shifting.