vibation issues

[burban1500]

Got the one tons in the burb and took her for a ride down the beach to make sure everything is good. I have a vibration at about 5 mph coming from the rear. everything up front is nice. It starts to wiggle the truck at that speed then goes away at about 10mph. It only happens when the truck is under a load, for instance soft sand. you cant feel the vibration on the road. All other speeds are fine smooth no vibration whatsoever. I set the pinion angle by eye when i welded the perches. I never used an instrument to check the angle but i am thinking i might need shimming. The angle is not harsh by any means but maybe it needs minor adjustments. The driveshaft i have was just remand about 2 months ago and u-joints are new. Im running 6'' springs with a 1'' zero rate. Where do i start

 

[Mudstud]

Doesn't sound like you have a problem at all. If it drives on the road fine then you're good. I wouldn't consider a vib on sand to be worthy of a fix.

 

[burban1500]

I use the truck on the beach often usually about once or more a week for several miles at a time. It shakes the truck and kind of pisses me off. i would like to try and correct it if possible.