411B hydraulic problem

The control valve body for the 300 and 300b is p/n G1231 and for the 400b the body is p/n G1281. The control valves share many of the same internal parts but looking at the pixs in the parts manuals it appears the castings are different. The control valves may not be interchangeable as a complete unit.

Gaskets from Case are the way to go but if you have to make your own, I use chart paper for this type application. Chart paper is about 0.005" and dense enough to be somewhat forgiving if your torque is less than perfect. I use a metal-metal sealant, apply and wipe off any excess, allow to dry beyond tacky but not fully cured.

I am probably missing something but having a hard time seeing this as one problem of a leaking lower control valve spool. The hitch movement when you move the upper spool indicates that the lower spool is leaking but with the upper spool in neutral and lower spool moved to the lowering position the hitch should not rise unless the spool in the interlock block is moving late and not far enough to fully uncover the return port. The service manual fix for insufficient movement of the interlock spool to relieve back pressure is to add another gasket to the forward interlock cap. Also if you have the older style interlock spool with the one end chamfered, the chamfer end must be installed oriented to the forward end of the interlock.

Joe

The following is just a shot in the dark as the hydraulic flow charts, except for neutral position, are not in my service manual so I am basically just guessing here, perhaps Roger can correct me.

When you move the spool in the upper control valve to actuate the remotes you are closing off the pump return port to the sump, as well as, simultaneously opening the supply and return ports to the remotes. That means that your lower control valve has the same pump pressure as you are delivering to the remotes.

If the lower control valve spool is leaking or out of neutral, the resulting pressure would tend to raise the eagle hitch piston since the upper control valve has the pump return passage port blocked.

The double-acting and single-acting interlocks are identical except that the center port is open on the single-acting block and you have to install a pipe plug in there to use it on double-acting systems. This center port appears to be in communication with the sump via a passage in the control valves casting independent of the spool position.

I was just wondering if some where along the line your upper and lower interlock blocks were swapped or the lower interlock block center port still has the plug. And even so would this cause the problem you are experiencing?

Joe