power steering problems/630

[Rich M]

Helping a freind with his newly aquired tractor that came to him in parts.After starting the tractor the steering wheel turns hard to the right. Have tapped the steering vale assembly back and forth with no change.tractor is full of john deere power steering oil.no air bubbles in resourvoir.Thanks for any and all help.

 

[F-I-T]

I would first jack the front up, engine off, and see that the wheels turn easily both ways. You're checking that the sector anmd worm are not binding. Then start the engine and see that it is still easy, as wheels off ground should not call for P/S assist.

Centering that valve won't cure a hard in one direction problem. Generally that occurs when the pins and cam faces get a worn spot that will not allow the cam and pin action to occur with a reasonable amount of steering wheel effort.

There is likely a divot worn in the cam face a bit off center, that is catching the pin and not allowing it to slide across the face. As you turn the wheel, when you get wheel resistance higher than the spring pressure in the actuator valve, the shaft tries to turn, but the front end resists. You continue to turn, the pin climbs up (in one direction) or slides down (for the other direction) it deflects the lever attached to the poppet valve, which gives boost in the direction you are calling for. If that pin catches and can't slide, the boost does not occur.

To repair, you'll need to remove the actuator valve, replace the pins (they're cheap and vital..they can't be allowed to fit loose or you risk a sudden tragic lock up), then use a die grinder and carefully dress the cam form back to smooth. It's actually a slightly over 1/4" wide slot at a 45* angle. Not too critical, just needs to be metal on metal sliding smooth. They tend to form divits in the center from years of sitting in one spot and bouncing a bit, but eventually they get a harsh edge on one side first, coupled with flats worn on the the two pins, and that's when they catch. Mark the position of the actuator valve before you remove it, but you'll still likely have to recenter it after reinstall.