What's your caster set at? That is probably the most common cause of death wobble. Make a line through the two balljoints and measure that angle with an angle finder. It should be about 5 degrees with the top further toward the rear of the truck. The amount can vary a bit, some people like as much as 15 degrees, but it should always have the top balljoint toward the rear of the truck. This should be measured with the weight of the truck on the axle.
If that's good, make sure you don't have loose steering or suspension components or bad balljoints.
Basic range of caster is 3 to 8 degrees, anything less and you'll have poor tracking, return-to-center steering and death wobbles, anything over may cause problems with tracking or a little extra effort required for turning, although "some" rigs do tend to do better with the 9-15 range. I just went through hell with mine until I got it set at 6 degrees. (full width HP D44 on 84 XJ)
I know you're a newbie and all, but did you even read my reply to you on this very post? I told you how to measure it, scroll up and read. A quick search on caster would have told you the same thing. As for adjusting it, you have two options. You can rotate the entire housing to the desired caster, or you can cut-and-turn the knuckles. You decide. If you only need a few degrees, spring perch shims or hangers and shackles can be used. Those basicly just rotate the entire housing, like moving the perches would.
BTW: Don't be afraid of the cut-and-turn. I know it sounds like a big deal, but it's really just time consuming. Of course, you have to be able to weld them back on or know someone that will do it for you. I got my knuckles off in a few hours of work. Grind the welds, heat them with a torch, beat them with the BFH. Then just put them back on at the angle you need and weld.
REMEMBER: Caster is checked and set WITH THE VEHICLE WEIGHT ON THE AXLE. I just put the axle on jackstands with the springs still attached.
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