I recently bought a 1984 chevy 1/2 ton 2wd stepside bed truck.I was driving it on a wet day and found out it only had front brakes.While doing a complete brake job I found out the previous owner changed it over to a 3/4 or 1 ton system.The truck has 8 lugs front and rear.The rearend is a 14 bolt saginaw with 13 in drums.It still had the 1/2 ton booster , master cylinder and proportioning valve.I bought the one ton booster master cylinder and installed them.The original proprotioning valve was rusted and stuck.Once loosened up, now the rear brakes lock up well before the front does.I have bought three proportioning valves from the dealer ($300.00) did not help.I bought a adjustable valve from summit.It helped a little ,but rear still lock up first. I was told that I need the factory brake code.The Autozone guys said it was a JB7 brake system.The Chevy dealer was NO help !!! Do you have any ideals? Any help ????Everything is brand new... I don't want to change it back to the 1/2 ton set up ,But I think it is my only fix.Very costly..The factory made heavy half tons and 3/4 ton camper specials with basically the same set up.The dealer said that their our about 30 different proportioning valves for the 1/2, 3/4, and 1 ton trucks I can't keep buying valves until I find the right one.They are non-returnable and $100.00 each. The tire size is 32 x 12.5 16.. Any thoughts????