|
Hi Tim, There four valves in the control block: (A) lift valve aka pressure control valve.
(B) lift check valve.
(C) release valve.
(D) relief valve. (1) When the engine is running with lever in neutral position the pump circulates the oil in the system and back to the torque tube via (A). (B), (C) & (D) are closed. Pump press is only that required to overcome friction to oil flow through the open system (guessing less than 10 psi). (2) Lever moved to raise position closes (A), pump press builds up overcoming spring on (B) admitting oil to piston. Pump press continues to rise to overcome weight on draft arms up to the 800-900 psi setting of (D). (3) With draft arms lifted, lever moved to neutral, a spring opens (A), press differential and a spring close (B). (C) & (D) remain closed. System is back to (1) above with pump circulating oil. Oil on the piston is in a hydraulic lock due to closed (B), (C), & (D). Oil press on the piston will be only that generated by the weight on the draft arms. (4) Lever moved to lower position opens (C) dumping trapped oil on the piston back to the sump and draft arms drop. (A) is still open, (B) & (D) remain closed. The draft arms can only lift when you start the engine and the lever is in neutral position when the return to the sump is restricted or blocked. Since your draft arms will drop when the lever is moved to the lower position, that block can only be (A) stuck closed and or the spring is broken. You have probably been operating the pump at full pressure circulating oil only when the pressure opened (D) at 800-900 psi with the same constant pressure on the piston. When you put the lever in the lower position, (C) opened and the pump simply did not have enough capacity to overcome the pressure drop plus the weight of/on the draft arms. So now that it won�t lift at all it is possible that the pump is shot (or shaft key sheared?) from running up against relief pressure nearly 100% of the time (doubtful). (D) is now leaking and/or spring is broken (maybe). (C) is now stuck open and/or spring is broken (likely). Or a combination of above. The are many reasons for a hitch that is operating normally to stop working I.E. sump low or dry, air being sucked into the pump, depth control lever or pin broken, lash setting screw(s) loose/backed off, etc, etc, etc. You have been operating with one problem and have now developed an additional problem. There is no doubt that your lift valve is stuck closed and/or spring is broken. It is likely now that the release valve is stuck open and/or spring is broken. Sorry for the long post, I am just too dumb to figure out a way to shorten it and get the point across. Joe
| 
