i just installed rear disc on my 91 z28 this weekend from 84 camaro. i took the spring from inside the 84 prop valve and put it the 91 prop but kept the same valve inside from 91 prop. the 84 spring is shorter then the 91 spring, hoping it will get more brake fluid pressure to help the rear brakes, so far it has worked out good, so far..... has anyone done this or know of this, so far neither front or back disc has locked up.