Universal guide to locking a tranny in second gear?

I'm in the process of converting my GST to brushless. I don't really have much knowledge about R/C cars yet, as I don't have much "hands on" experience at the moment I'm trying to learn more now, though.

I need to lock the tranny on my GST in second gear, but I don't really know how. I've tried searching for some guides, but I couldn't come up with anything very useful. So, I was wondering, does anyone have a (somewhat) universal guide to this process? Would be much appreciated!

And any more info on brushless conversion in 1 place would also be very nice.