Yesterday I had to drive my sig truck across a muddy field to pull out another truck that was stuck. It was really soft so I locked the hubs, put it in 4H, and hit the throttle. The truck was moving along easily at about 40mph when I turned the wheel to the left and it started shaking violently. It does this every time when I turn left or right more than about half lock at speed. So I put the hubs and t case back in 2H and drove with the same driving style in some lighter mud. The shaking didn't occur this time. So I locked the hubs again and put it in 4H. Turn at speed and it shakes badly! What could be causing this? With it only being while turned I'm thinking it could be steering play (play in pitman arm, tie rod ends, steering box, etc.). The steering has a good bit of play in it so I think it might be the slack in the steering cycling while turned can cause what I described. But being only in 4x4 I'm leaning mor towards driveshaft vibration or something in the front axle

 

Have you checked your u joints or shaft bearings at the knuckles?

 

Seized U-joints are very common in these trucks as most owners rarely engage the front drive system so if you have never serviced the front axle you are advised to put an overhaul on the list. But also note that even with brand new joints you may experience some binding of those joints near full steering lock, so if you feel vibration or noise just reduce steering angle slightly.

 

i advise checking the front axle and u joints, the u joints on my 94 f150 5.0 seized up one time, i had just used it for snow plowing a week before, i pulled into the farm saw it was muddy locked hubs slide in 4 high rolled ahead lightly hit the gas and boom clank clank clank with a crap ton of lurching as well. siezed u joint didnt want to turn and when i hit the gas it broke, taking out my outer stub axle as well. that was spendy