Need help with powertrax setup for older car.

[Street Fighter]

I installed a powertrax postive kit for my 77 camaro and thought that everything was find,but according to the final check it's not. They claim that you should be able to hold one wheel and that the other should not be able to move in this direction inwhich I'm Holding ,but in the opposite direction.When I tried it both wheels goes in he same direction.I checked a limited slip rearend and that's how it works, but this is surpose to be better than the stock setup.Have anyone had any dealing with this unit? If so tell me what I did wrong. We are not talking about a stock rear so I don't need to know anything about the stock rear.But only if you have done one of these.Thanks Street Fighter.