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I have a 1993 426 backhoe I was running it real easy and the

I have a 1993 426...
I have a 1993 426 b backhoe I was running it real easy and the dipper stuck engaged to dip out at the valve body the plunger is stuck down or engaged whats causing that and what is underneath if I take the top bolts out I need a picture of what is in there I'm in North Pole ak and its getting cold now and I need to get my hoe home
JA: What is the complete model and serial number of your machine?
Customer: 426b 5yj is the beginning and is all they ever ask me for I would have to go look and its ten miles away
JA: Anything else you want the construction mechanic to know before I connect you?
Customer: I just need to know y the plunger stuck and how do I fix it I have no book is it magnetically charged
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Answered in 6 minutes by:
10/22/2017
catmastertech
catmastertech, Technician
Category: Construction and Road Equipment
Satisfied Customers: 2,391
Experience: Field service technician for CAT 19 years.
Verified

Hello,

Most likely something is broken in your cylinder and has flowed back to the valve causing it to jam.

You will need to remove the control rod from the top and the cap from the bottom to remove the spool from the valve.

You should first remove the lines and fittings at the valve to see if you can identify the debris that is stuck in the spool.

Note: if you have been working in deep water or a corrosive environment, the debris could be in the bottom cap and binding the centering spring.

I will look for some parts pictures and post them here to help you.

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Here is an image of the valve section

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Depending on the debris you find, you will at least need to replace some lines or rebuild the stick cylinder. If you find large pieces of metal or fine brass metal in the oil, you may need major system repairs and clean-out.

I often see damaged hoses send debris into the valve and also damaged cylinder was send metal into the valve.

Look for damage signs of pinched hoses or dents in the cylinders. It is possible for the debris to come from anywhere in the systems but, start at the failed valve system first.

catmastertech
catmastertech, Technician
Category: Construction and Road Equipment
Satisfied Customers: 2,391
Experience: Field service technician for CAT 19 years.
Verified
catmastertech and 87 other Construction and Road Equipment Specialists are ready to help you
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Ok, does it move any? Can you turn it? What did the oil look like? Was any metal seen in the oil?

The Allen head is the primary resolver check valve. It is not related to your problem.

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It is part #21 in the parts image I sent you.

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Customer reply replied 28 days ago
Their is nothing in any port I used a magnet and the oil was fine no metal or shavings I cannot get the valve to move more that 3/4 “ and it hits something hard

Since you do not find metal, I would suspect a piece of hose is jammed in it somewhere.

Have you tried taping it down to see if it will move further?

Snow, it was 80 and humid here today.

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Have you noticed any damaged hoses?

It is possible the debris came from the supply side or flowed from the return ports and is debris from another cylinder or hose.

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I am not seeing any replies if you are posting.

I just want to add, at this point your options are limited.

You can keep working the spool up and down and tap on it to loosen the jammed debris. If you hit it too hard it may seize in the valve. Keep working it in both directions and hopefully, it will begin to move better. Use a brass drift or piece of hardwood to strike on the spool instead of hitting the spool directly. The brass or wood should not damage the spool if you need to hit it harder. Just don't try to drive it out fully in one direction, when it starts to move, keep pushing it back in to prevent too much scaring or the bore. You can polish the spool with fine emery cloth if needed.

The other option would be to remove the complete valve bank and try disassembling it on a bench. Or lastly, replace that section.

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Customer reply replied 28 days ago
Thank you for your help I think I got it now I’ll post a pic , i piked the frozen dirt and after looking a picture it has two of those pressuer reliefs I wasn’t sure but I’ll take that out in am and I think I’ll have it now I can see when crawling under it fully thanks again

Ok, thanks for the reply.

The relief valves will not cause the binding but, they will help you flush out any debris in the valve.

Attached is a cut view to show you the lands of the spool. These passage areas are where trash will get stuck and jam the spool.

You can also remove the load check valve to help flush out the passages.

The only items not shown are the resolver check valves.

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Customer reply replied 26 days ago
Ok I took it all apart and something passed thru it three spots were gouged up on the bottom I used oil and fine emery cloth and debured it made it smooth reassembled with petroleum jelly and it went it pretty easily only the two spots at the bottom where it was gouged up did it get kinda a little resistance so I used machine on job for two hours and it did it again but I was able to get the machine home to pull the whole valve body for all the functions and I’m gonna take it apart and hone it and see if I can’t find another one

Thanks for the update. If it stuck on the same valve, you likely have something seriously damaged done stream.

You must check the cylinder and its hoses for damage and make repairs or the metal will begin sticking in other valves or even destroy the hydraulic pump.

Once you find the source of the debris, a flush of the hydraulic system should be done and filters replaced a few times to remove all the debris that is floating around in the system.

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catmastertech
catmastertech
catmastertech, Technician
Category: Construction and Road Equipment
Satisfied Customers: 2,391
2,391 Satisfied Customers
Experience: Field service technician for CAT 19 years.

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