89 F150 4x4 - Hard Turning

All of a sudden, truck is very difficult to turn sharply at slow speeds, shudders and jumps almost like it is in 4 wheel drive mode. Locked manual hubs and engaged 4 wheel drive, vehicle acted as it should but returned to same hard turning when in 2 wheel drive. Truck drives fine straight at any speed with no noticable noises. Could the wheel bearings have failed suddenly, or is there another possibility? Any help would be greatly appreciated!

The front axle U-joints are probably siezed and it don't matter if you are in 2wd when this happens. If you are lucky, it's just the outer 2.

Jack up the front end so both wheels are off the ground and then safely put it on stands. Now go to one wheel and try to manually steer the wheels. Rotate the tire in 1/4 turn increments and repeat. If a joint is siezed, you will be able to tell.

Thanks Johnny, I will give that a try today. Whould the u joints seize up without any warning signs? How difficult to change?

jacked up front end, turned wheels without problem, however power steering fluid was coming out of the cap (not on correctly). I have noticed a hissing sound while turning at slow speeds lately. Could there be air in the system, or is the pump just bad? When I checked the wheels there was no movement from 12:00 to 6:00 so it seems the wheel bearings are okay?

If I change the fluid, and still has same symptoms, should I then replace the pump?

No, it is not the P/S system or the pump. You may have got air in there from the loose cap. Just keep it full and it should straighten out when the air bleeds out.

The symptoms you describe are a binding U-joint. Maybe it's only doing it under load right now. They are not that bad of a job to replace, but the bearings in the hub require a special socket and lots of time to make sure it goes together correctly.

Everything has to be cleaned, inspected, and re-packed with new grease after you get the axles out and replace the joints. Don't mess with the right side inner u-joint unless it is bad. Removing that makes this job 10 times more difficult.