With car jacked up rear wheels off ground manual trans in gear i can spin the rear wheels of the car and driveshaft doesn’t move is this correct?? I did a pull with my new 408 Lsx /t56 afterwards noticed vibration from rear and jacked up to check things out

 

If you turn one rear tire clockwise, does the other one turn counter-clockwise??

 

yes it does

 

Then everything is working as it should, except if you have a clutch type posi unit, then it's just worn out. Not saying something isn't worn or there's other issues...but it functions correctly.

 

thanks

 

Yup... an "open" (unlimited slip) one, or one with a typical Auburn "posi" (limited slip) the majority of which are totally worn out and non-functional, or for that matter an Eaton Gov-Bomb "posi" as long as you don't turn the wheel too fast (it's easily possible to spin a wheel fast enough by hand to lock up a Grenade-Lock), will do that.