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case 680 hydraulics

wyley1 I have an 1988 case 680- replaced all seals and the boom still wants to slowly fall down. The 2 cylinders which support the boom slowly allow the boom to creep down. Any suggestions, I do not know what the problem is. (weak hydraulic pump?)
AJ A bad pump will not cause the boom to drop,when you lift the boom up and let the lever return to neutral the oil is trapped between the control valve and the pistons in the cylinders,if the oil can escape the boom will drop,if you are happy with the cylinder resealing job and you have done both cylinders that leaves the control valve and that circuit relief valve(port valve)that could be leaking,there is an o'ring and backing ring on the circuit relief that can fail,take out the whole valve without altering its setting and see if the o'ring is good and there is nothing holding the valve off its seat,if thats ok,take off the rod from the spool valve and turn the valve 180 and reconnect the rod,the idea been if the spool and bore is scored turning the valve moves one score away from the other,at my place we have a valve to put in the line,ie lift the boom up with the inline valve open,close the valve then and see if it comes down,if so the problem is in one of the cylinders,if it stays up the problem is in the valve.
Good luck
AJ



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