Crazy power steering

[RIGEROUS]

 My 1986 Scottsdale has developed some bad habits in the steering department. Sometimes it works fine, sometimes you can not turn the steering wheel even with excessive force, (much harder than with the power steering disconnected). The scary thing is sometime the truck will unexpectedly dart to the right or left when driving. I just changed the pump and fluid but that did not fix it. Wondering if the steering box internals are bad, sticking hydraulic valve Any ideas would be much appreciated.

[zieg85]

is it a 4x4?

[VileZambonie]

I would check the front end out thoroughly.

[Dave Kay]

Bendix-type power-booster or vacuum powerered steering?

[RIGEROUS]

It is 4x4, just a high pressure and return hydraulic line from the pump to the box, no vacum lines. Can't find anything wrong with the front end parts either. Could it be inside the steering box ?

[VileZambonie]

Jack it up and check the ball joints, check the front end dry parked on the ground. Check the steering shaft and coupler. If everything checks out ok remove the pump from the equation. If it's still sticking or binding get a new gear box.

[thirsty]

check your universal joints also. I've had the same problem before and found that the u-joint was seized up on two of the caps not allowing it to turn correctly.