Squat Check and Question

When ever I squat I find that my right glute is not working as much or at all when compared to my left. By that I mean on my way up I don’t feel the glute been simulated at all. Any idea out there why and what I can do to fix that?
On a side note I use Eric Cressey “10 Uses for a Smith Machine” http://www.T-Nation.com/readArticle.do?id=810548
to get my hips going.

I also do single legged bridges to get the glutes fired up but that does not seem to help. One more thing while doing the single legged bridges I note that I am less stable on my right side then left. I hope some of this can help.