It is probally a shuttle valve in the remote stack
Stuck, damaged or leaking shuttle check valves.
Lack of hydraulic flow from the rear remotes is usually the result of one or a combination of the following:
1. Leaking secondary shuttle / load sense check valve or shuttle check tee in the sense lines.
2. Secondary shuttle / load sense line check valve leaking in one direction only.
3. Leaking primary shuttle check valves.
4. Flow control / load sensing piston sticking.
NOTE: Depending upon the tractor series, check valves may be referred to as shuttle check valves or load sense check valves.
NOTE: the following presumes that main pump and three point hitch are operating at specification.
To troubleshoot the remote valves:
Install a flow meter at the remote coupler. If there is flow with no load then proceed with items 1, 2, and 3 below. If there is is no flow at all, start with item number 4.
1. Install a 207 bar (3000 psi) pressure gauge in one of the 'raise' remote couplers. Simultaneously move all remote valve control levers to the 'raise' position. If system specification pressure, +/- 7 bar (+/- 100 psi), is observed, the problem is a leaking secondary shuttle check valve or shuttle check tee.
2. Repeat the test at a 'lower' port. Move all handles simultaneously to 'lower'. If system pressure, +/- 7 bar (+/- 100 psi), is observed, the problem may be a secondary shuttle check valve leaking in one direction only.
3. Inspect the secondary and primary shuttle check valves, their o-ring seals, or sealing surfaces for contaminants, scoring or damage. Primary and secondary shuttle valves and shuttle check tee is the circuit by which pressure is sensed at a working coupler and communicated to pump. A shuttle tee may also be located in the sense line of other functions, such as steering or if a second valve is supplied by the same pump. Load sense check valves are located in the remote valve sections, in the interconnecting load sense line. The primary, secondary, shuttle check tee, and load sense check valves are all described in the Hydraulic Section of the appropriate repair manual.
4. If operation of the shuttle / load sense check valves and tees have been checked and remote valves still do not operate, check for a sticking spool / piston in the load sensing valve assembly on the pump. Contaminants introduced accidentally at the couplers migrate through the load sense circuit to this valve. If sticking is caused by very minor scoring it may be possible to lap the lands of the bore and spool with Crocus Cloth to effect a repair.