'51 8N 3PH won't raise or lower

Remove the inspection covers.

Check the operation of the control linkage per the I&T manual. Adjust as required. This may be all of your problem. If you cannot get the adjustment or it will not work consistently, then your problem most likely lies in the control linkage in the top cover.

Put in about 3 gallons of oil, or until the oil recahes the underside of the check/relief valve - that's the thing on the back of the pump body, looks kind of like a big spark plug. Hang a load on the hitch.

Start the motor, engage the PTO, select "lift" and look inside. You're looking for oil leaks. In approximate order of likelihood, oil may be leaking from

the piston/cylinder
the check/relief valve
the exhaust valve (look for turbulence in the fluid below the check/relief valve)
the pump-to-base gasket
the cover-to-case gasket
the cylinder-to-cover gasket

Only when all these have been eliminated, should you consider the pump to be suspect. They do go bad - but not nearly as often as all the other things listed.

To remove the pump, first drain the oil, and remove the PTO shaft - four bolts on the bearing haousing, then slide it out backwards. Then you can remove all the pump mounting bolts from below and lower the pump. Be careful, it's aluminum and will not stand a lot of abuse.

But first isolate your trouble.

llater,

llamas

Are you sure that the control arm coming down from the liftcover inside is engaged with the rocker on the pump? Feel behind the pump through the right side inspection cover and make sure the control arm ball end is in the pocket of the rocker which controls the valves. It should move the rocker back and forth when you actuate the position control arm.