center diff in my revo.
 

is it really necessary to run a rear brake if i use the cd? i just wanna be able to mash the throttle and not wheelie.... right now im just using to motor brakes

If you don't run a rear brake your brakes will be front only or very little stopping power at the rear, depending on how thick your CD fluid is.

I had this setup in my old race revo- its nice on dirt as it lets the rear loosen under breaking and lets the truck turn