Fast Hitch Settles Down

The fast hitch on my Super C settles down overnight. What cause that and how can it be fixed?

You need to determine if it is the cyl or the check valve. Unhook the hose to cyl that is not holding hitch up, no oil should come out of cyl, if it does, cyl it is leaking internally. If that checks out ok, move to the check valve block and determine if oil is leaking back through check valve on side that is holding hitch up or just take the plugs out and check balls and springs etc. O-rings on piston in check valve can leak to return side also.

Retcol: By the time you reach the SC age you may settle overnight as well. It's 55 years old, has every right to settle.

Seriously, two possible problems, either the hitch check valve, that steel block where plumbing from cylinder meets plumbing from control valve, or you have bypassing within the hitch lift cylinder.

Lift cylinder is easy any hydraulic repair shop can rebuild that. The check valve may be a bit of a challange, check with CaseIH, they may still carry the internal parts.

Well let me tell you my story. My FH was letting me down, literally. I took the hydraulic cylinder apart and replaced the o rings. That was an easy fix if I can do it anyone can. The only “press on” part is the dust seal and that is easy to push in.
The o ring that is likely to be the problem is the one on piston head. Mine was broken, and I just got the seal kit and replaced them all. I used a bit of grease to reinstall everything and it all went together well. I screwed the pipe fittings back on to install the hydraulic hoses and I tightened them too tight and split the cylinder head. So I had to take it all back apart and I braze it, [moral of the story watch how tight you are getting them]
I had a rebuilt pump, I had a rebuilt FH valve, and a rebuilt cylinder. I thought MAN I am good to go. WRONG! **#$^$(@^(@*^$$(*^&$^%&^$%.
Was all I could say when I went outside the next day to a FH sitting on the ground. Well I went to my manual and started to read. What I didn’t know was the button on the top of the cylinder is the valve stop limit. That button MUST be pushed down to “lock” the cylinder in place. It changes the cylinder to be in that place until the lift is raised. So I put on my blade for some weight and set the limit stop. After three days it was still in the same place.
If you think your cylinder is good you can test it by setting the collar stroke limit to push the valve down. Turn the tractor off with the valve pushed down and see if the FH drops. If it does fix the cylinder it is easy to do just don’t mess up like I did. Ron