J55 HD Brake size help

[RodsGreen10]

Originally Posted by oneday1

I need to purchase new wheel cylinder, however, I am unsure as to the size. Most places have the options of 15/16 or 1 inch bore. How would I go about checking that? Or find out from the J55 HD BRAKE SYS code on my build sheet?

Call parts store they should ask you the rear drum size. Use the listing below to get the correct size. That's what I did. All good now. I have the JB5 on my truck.

According to the Chevrolet 10-30 series light truck service manual:

JB5= front disc 11.86X1.29 rear drum 11.15X2.75 Vacuum-Double Diaphragm

JB7= front disc 12.50X1.54 rear drum 13.00X2.50 Vacuum-Double Diaphragm

JB8= front disc 12.50X1.54 rear drum 13.00X3.50 Hydraulic-Hydro-Boost

JB7 is basically Dana 60 Front disc with the smaller 14FF drum brakes with a vacuum booster and JB8 is Dana 60 front disc with the Large 14FF drum brakes with Hydro-boost.