no, you dont need diff axels. i also had the same problem as you did. I ruined my shifter fork in the si racing, and now i'm using the dx tranny. Works great for saving gas, but...my acceleration sucks horribly. Now i'm not racing any more. I bought another Si tranny from icantgetno or ..damn forgot his name on this forum. Oh well, i can't wait to put the si tranny back in
