Ok so I have done a little research, if it won't lower and, release pressure, linkage is good, according to my official allis chalmers it shop manual,,, implement raises but will not lower: hold valve not opening, hold position link rod incorrectly adjusted, binding implement and or Rams. If I read this correctly it would have to be in my hold valve, happened outa the blue so no adjusted or tampering with linkage, can pull plug at hold valve and Rams will release, so I have a hold valve issue, how does it work, I'm quite technical but can't find a good description , only has two ports, inlet and return I'd assume, if anyone can help me please let me know thanks Dusty