I have a 644d-34 that will not lift or brakes. However, if you turn the steering wheel it will lift and the brakes work. As soon as you stop applying pressure to the steering the brakes or the lift will not work. The steering works all the time, but nothing else works unless pressure is applied to the steering. Any help would be greatly appreciated.
What have you tried by way of diagnosing this problem? What year is the machine? Do you have an operator's manual? Sorry for all the questions.
We will need to know if there is pilot pressure at the joystick (or both joysticks if so equipped) when the steering is not being activated. There should be a test port on the secondary function manifold marked PPG. Also, there is a load sense test port on the same manifold. This is a load sense for the power steering unit circuit. We need to know if the load sense signal is present when not steering. There is a check valve at the LS port on the Power Steering Unit. This has been known to stick open and cause steering/boom function issues.