if you go hit HPI's website there are illustrations..

I'm not sure of all the ins and outs, but the X allows things to be rebuilt and come apart a lot easier, I guess on the previous ones a lot of stuff had to come off to get to a diff or whatever, now it's like 6-8 screws and the thing is in your hand ready to rebuild.. total dissassembly the other night took all of 15 minutes or so and I had all the components sitting out (diffs, tranny, engine, etc)