I installed a 3/4 ton axle settup and I replaced the master cylinder with a 3/4 ton. This blazer is a 1990, and the ABS computer is long gone. The brakes seem to work ok, but I don't understand what the ABS did before. Would it feed the proportioning valve somehow? Should I use a different proportioning valve? The new master is a new Napa master with the application for a 1990 3/4 ton. The reservoir on it is a little smaller than the old one, and the back brake line tube has a bigger orifice than the old one.