450 boom hydraulics

[SEAL]

I have a JD 450 and am experiencing a problem with the boom hydraulics. No matter weather I push the spool (in the boom control) in, or pull it out, I am getting pressure to the back of the cylinders and dumping the bucket. If anyone can tell me what can cause this I would be grateful.

[digitup2]

Did you have any hoses off this unit .Digitup.

[SEAL]

I had all of the lines going forward off in order to remove the cab (fuel tank hydraulic tank and seat) to gain access to the steering clutches which I repaired. I broke the lines at the point where you step into the loader. I have followed all lines from the control valve to all 6 forward cylinders to be sure they are correctly connected. Before the work the hydraulics were working correctly.

[digitup2]

Check and double check your hydraulic lines to see if you have two lines mixed up on the specific hydraulic ram set in question .I am thinking one set of hose are backwards but to the right ram if you know what I mean .I have done this before and It took me some time to figure it out .Digitup .

[SEAL]

Digitup javascript:emoticon(':?:')
For my education please help me understand. The way I see it, if I had 2 lines reversed on one of the rams in the bucket dump circuit I would have one cylinder pushing and one cylinder pulling at the same time when I push the spool in. Then the individual cylinders should reverse their pushing and pulling when I pull the spool out. If I am wrong about this please help me understand where I am going wrong.

[SEAL]

I just went out and switched the two hydraulic lines on the right cylinder. The rams acted just as I thought and stated above, one in and one out. After I switched them back to their proper place I was working the cylinders and I noticed that the power out that dumps the bucket still works as normal. When I try to pick up the bucket by moving the spool just a little bit it rolls the bucket up very slowly and if I go past that little bit open point to all the way open it stops rolling up and goes into dump mode at normal speed. There is obviously something wrong inside the valve but I have no idea as to what it could be.

[digitup2]

The only other thing would be that you have an o ring going bad in the valve bank this could be your next area to look at .Digitup.

[SEAL]

I took it to the local hydraulics dealer because he told me that what I said it was doing was not possible. He put it on his tester and sure enough it pressurizes the dump port on the valve whether the spool goes in or out. They replaced all the soft goods and did a test to check for cracks and found none. The whole shop is mystified. The shop owner and I have talked to the people John Deere says are the best they have on this valve and they say this is not possible.

This is a regenerative type valve that allows quicker dumping of the front bucket when it is loaded.

I think I have a good candidate for stump the experts.

[SEAL]

Well here is an update. My crawler is back in business. I would love to tell you all what was wrong but the hydraulic shop doesn't know. After the second tear down of the valve they couldn't find a problem so they put it back together and it started working properly. A mystery unsolved but at least it is working.

[jdemaris]

Well here is an update. My crawler is back in business. I would love to tell you all what was wrong but the hydraulic shop doesn't know. After the second tear down of the valve they couldn't find a problem so they put it back together and it started working properly. A mystery unsolved but at least it is working.

It sounds like your valve-assembly has some sort of anti-cavitation, or lift-check valves - and something went wrong with one of them. I recall having a few weird issues like your's with older 350s and 450s. Seems if all is working OK, then maye one was stuck, and is now un-stuck. I know at least one version used in the Gresen valves was plastic or nylon. If it stuck once, it will probably happen again.

I've got an equally troublesome problem right now with the hydraulics on my IH backhoe. It has nothing to do with Deere, but is at least, just as confusing and also caused by the same type of valves going bad.

My IH hoe has a open center system, just as a Deere 350 or 450 uses. But . . . one gear pump runs all the backhoe and loader functions - except for the swing. For some strange reason, IH uses the gear power-steering pump to power the swing and steering only. So, the backhoe has two totally separate hydraulic sysems that should have nothing to do with each other. They only connect at their suction lines at the common oil sump. Well, I found out, that when the backhoe gets hot, the hydraulics get so weak the boom won't even raise. But, I found out by accident, that if I hit the right or left swing lever, while trying to raise the boom, the boom then comes up great. Impossible, right?? Well it cannot be impossible, since it does indeed happen. Keep in mind, there are two separate hydraulic systems, with their own pumps an own valve banks (not tied together). I later found out, even though it does NOT show in the hydraulics schematic, that one of those anti-caviation valves in the boom-lift valve, is connected to the swing valve. So, if you jam on swing, and crack the relief valve, oil backfeeds to the boom if that valve is stuck.

Don't hurt your mind over this IH thing. It aleady hurts mine. But, somethings, things are not quite as they seem to be.