just wondering if anyone knew a cheap way to put disc brakes on the rear axle. i have plenty of parts off of front axles but im not sure if i can use anything more than the calipers.

search in the toy forum. Check the FAQ.

like these?
http://www.ruffstuffspecialties.com/catalog/adapter-pattern-caliper-p-271.html

Like what? I can't see past your avatar.:D