VAC-14 Eagle Hitch Drops When Tractor's Not Running

I am just now getting to determining why my lift arms settle when tractor is not running. It has been suggested I disconnect the vent/leak off tubing from the rock shaft and cycle the arms up & down about 10 times, then lift arms up with tubing still disconnected. Any persistent leaking would indicate leaky O-rings in the lift cylinder.

Question is, is tractor running when I cycle the arms up/down 10x?

Hopefully I have explained the situation clearly.



Thank you,
Glenn F.

You cycle the lift with the engine running and with the control. What that does is if the cylinder if leaking will have oil come out of the vent when you shut it off with the lift up that tells you if the cylinder is the problem

Makes sense. Thanks, Old.

Glenn F.

What you are trying to determine is if the piston seals are leaking bye or valves in the control block are leaking back to the torque tube.

Piston seal leak bye oil ends up in the rockshaft housing and is conveyed back to the torque tube sump via the vent/leak off tubing. To check rate of piston seals leak bye disconnect the tubing at the fitting on the rockshaft. Cycle the hitch up & down about 10 times to clear any residual oil in the housing and to check that the leak off is not plugged. The leak off can get plugged with old, hard grease, if the rock shaft housing is tight you should be able to feel air puff out as the piston is forced down to raise the draft arms and a slight vacuum when it moves back up. After the 10 cycles, leave the draft arms up with preferably some weight. Any oil dripping from the leak off fitting can only be some residual oil or leak bye of the piston seals. The residual drip will eventually stop and any further oil leaking is the piston seal leak bye rate.

If the no oil is dripping from the leak off and the draft arms continue to drop there is a leak back through the lift check valve or the release valve. Pic is a simple drawing of the hydraulic circuit. In neutral control lever operation the control valve is by-passing the pump output back to the torque tube sump. When the lever is moved to the raise position the control valve shuts off the by-pass and pump pressure is directed to the top of the piston via the lift check valve. When the piston bottoms out, draft arms fully raised, the relief valve will lift if the lever is not moved back to neutral allowing the control valve to return back to the by-pass position. At this point with the control lever in the neutral position, the piston is in a hydraulic lock between the lift check valve and the release valve (red line). So we can see that the piston can not move to lower the draft arms unless there is a leak through the piston seals, back through the lift check valve, or through the release valve.

The lift check valve is under the plug that you can see on the bottom of the control block. It is pretty simple, just a ball, spring and seat. The release valve isn?t as simple, it is a two stage "slow drop" or "fast drop" valve depending on the position of the control lever so there are two potential areas of leak through on this valve. The neutral position actuator to valve stem lash (about 0.010?) needs to be correct for the two stage function. Other than setting the actuator lever lash on the control and the release valves it is best to have a manual before you start disassembly of internal control block components.

Joe

Did the ten cycles. Hung a cinder block on a lift arms. Had an oil mess on shop floor this morning & lift arms were all the way down. Took piston apart and both O-rings are worn out.

Thank you for your input.


Glenn F.