terrible rear end vibration after gray wire mod

so i done the gray wire mod and it worked great for one day..but then i was going down the road and when i hit 45-55 mph my rear end and on up my driveshaft vibrates and jumps like crazy so i undone the mod and re connected the gray wire but its still doing the jumping and vibrating does anyone know whats going on with my truck???

 

May not have anything to do with the grey wire mod......may be a bad u joint. Crawl under and heck to see if its loose or
can be shaken back by the rear end.

 

how do i check to see if its loose? that may be a dumb question but i have no knowledge at all of anything past the engine

 

definitely has nothing to do with grey wire mod. check your carrier bearing too, bu getting underneath and seeing how far you can move the driveshaft within the carrier (middle support in midpoint of truck) shouldnt be more than 1/4 inch. Mine is pushing beyond 1/4 inch, but I do not have the vibration issues you have. Definitely also check u-joints.

 

crawl under, grab your drive-shaft about a foot before it enters your diff and try to wiggle it back and fourth.

There should be no play, if there is it could be your u-joint or your pinion bearing.

 

Its pretty easy to check, on level surface, in park. Crawl underneath your truck by the rear differential & note where the driveshaft connects to the flanged yoke on the diff, grasp the drive shaft firmly with both hands & "twist " the shaft clockwise/counter clockwise looking closely at the U joint for signs of damage, movement between the Ujoint & the flange its connected to, there should be no movement (shit, wish I had a pic to show you ) The other check is while still grasping the driveshaft try moving it vertically up & down, then horizontally side to side . There should be no sloppy loose movement either up & down or side to side....

 

wait, were you driving on the pavement with the locker in?

 

no the locker is disengaged when it vibrates and its only around 55 mph when i get past 55 it stops and when im slower its fine as well

 

You weren't doing donuts on dry pavement with the locker on were you?

 

no all i done was do the mod go crank the truck in my grass lock it in 2hi 4hi and 4low..then disengaged it put it back in 2hi and turned my truck off..it worked then but when i went to work this afternoon the vibrating started so i undone the mod in the parking lot with my boss put everything back factory and now it still vibrates