JB5 brakes? Meaning 11X2.75" rear shoes? If you have the lightest 11x2 rears that may help up, the JB5 is standard on 1/2 Ton Suburbans. Cheap I understand... My $.02. I can tell you there is a world of difference between the 2 as I have them both, the lesser on my 86C10 and the JB5 on my 85C10, but I am comparing stopping stock tire sizes.