Only on front of 1988 truck and only in 4X4 with hubs engaged..Turn hard left or right , noise and binding ...Either way.....Disengauge and the thing turns fine still in 4X4 but hubs loose...Constant velocity Joints? Charlie

 

Are you on a hard surface when this happens? If so, it's normal. When you turn, the front wheels have to travel a further distance than the rear wheels. Since these vehicles have no center differential, something has to bind and then slip to accommodate the different path lengths for front vs rear.

On loose surfaces (gravel, dirt, snow, ice), the friction is low enough that the wheels skid easily and you don't notice this.

The solution is, don't run in 4wd on hard, dry surfaces.

 

RJR beat me to it^^^

Some binding is normal when wheels are hard over to one side, even when all parts are good.
Binding will be worse when CV joints are worn, or when torsion bars are cranked.
A locker in the differential makes this even worse.

 

Did you inspect all steering components in front? As stated turning 4X4 with hubs locked will increase stress on front including steering components. I used to go through idler arms.

Are tires rubbing?

 

I would have to take it to a knowledgeable mechanic...It is a stock 1988 with 148 K on it....I'll take it in and ask for a check ..The problem was on Dirt and pavement as well.

 

Nothing wrong with having it looked at.

Try taking a look yourself. Just for grins. Have someone in the driver seat with you at front have them turn wheels both ways to full turns both in and out of 4wd while you listen and try to isolate the noise. You can even raise one side at a time and try to manually turn the wheel at the tire by hand looking for any play or moving parts.

At least then you can have an idea of problem then have mechanic double check you. Don't tell the mechanic just see what he says. Might keep him "honest" so to speak.