This is not a shuttle valve problem. The shuttle valve is used to allow make up oil to enter the high pressure loop of the hydro. It has to switch each time the hydro changes from pulling to holding back. Problems with the shuttle valve will cause free wheeling and no-go situations.
This problem has to be caused by slow response of the pump servo.
The servo is a hydraulic cylinder that controls the angle of the swash plate of the pump. It works by having oil enter the lower pivot end of the cylinder and having a controlled amount of leakage past the piston to the other side of the cylinder and then using a variable orifice to change how much oil leave the cylinder. The surface of the piston is smaller on the inlet side than the outlet side of the cylinder. If the oil going past the piston can not get out of the cylinder, the equal pressure on each side of the piston will cause the ram to retract because that side of the piston has the larger surface and thus exerts more force. If the amount of oil allowed to leave the cylinder is the same as the amount going past the piston, you will get get no movement of the ram because the forces exerted on the piston will the same on each side. To extend the ram requires that more leave the cylinder than is going past the piston. The pressure will drop on the outlet side and more force will be exerted on the inlet side and the ram will extend.
The variable outlet orifice is controlled by mechanical linkage. That is what the control rod does that enters the hydro housing. Problem with the linkage will result is loss of control rather than slow response. Excess leakage through the piston or blockage at the outlet orifice will cause the ram to retract and not extend. Excess leakage at the outlet orifice will cause the ram to extend and not retract. This is not the problem you are having so you can rule out leakage problems in the servo.
Slow response will be caused by lack of charge flow and/or pressure. The charge pressure is used to make up oil in the high pressure loop and to control the servos. It takes very little pressure to add make up oil since it is only add to the suction side of the high pressure loop.
1) Check the oil level. Check with engine running at least two minutes.
2) Check the filter. The one you are concerned about is the one in the screw on canister.
3) Time to use a Flowrator to check flow and pressure in the charge circuit.
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