1980 Case 480C backhoe boom dropping like a stone.

The boom cylinder has been dropping very slowly for awhile, no real problem. Yesterday I was pulling posts (working hydraulics hard) when all of a sudden the boom dropped like a stone. No hoses blown. Had to rev engine to high RPM to get the boom to come up. As soon as I let the lever go back to the neutral position, boom drops fast. Drove backhoe back to yard, but had to hold boom lever in raise position so boom would not drop. Any ideas? Would it just be the cylinder packing let go or a deeper issue in the valve assembly. Pressure relief valve? Thank you in advance.
 
Gday Chris

Sounds like seals or piston has come off cylinder.
Or main relief for boom or cyl check valves if they have them.
If not too hard swap hoses from one function to another like boom to bucket or similar.
That will let you know if the problem is in valving or cyl.
Just becareful as oil under pressure can kill
Are there any other functions slowing or getting weak for if they share a relief
I see ebay seals around 20 bucks over your way
 
Thanks nobbie. I have the boom cylinder taken off, ready to go in for a new seal kit. All the other functions (bucket, dipper, stabilizers) did not seem to be weak before this happened.
 
Not sure labour costs over your way but here in Australia they are a killer so if you are mechanically minded they not too hard to repair hard part would be undoing gland but if you can cut and weld would not be that hard.then clean burrs off rod with a rubstone and take pic's as seals come off then reverse procedure to refit if inner gland seal stiff soak in hot water to soften.important to not cut any lips off seals
 

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