I have converted my 68RS to 4 wheel disc,and was concerned if the factory master and prop.valve w/no booster is ok for this swap?It was a 4 whl.drum set-up originally.It seems to work ok,but it this a problem?I am going to add a booster soon for a little power assist.Any thoughts on this subject?Thanks. smile.gif

what discs are you using? there are a lot of different sized calipers out there, and every different combination is gonna need a different master.
if you are adding power anyways, i would step up to some sort of 4 wheel power disc master.

factory drum master will hold residual pressure. you need a disc/disc master, such as off a 2nd gen T/A.-depending on the calipers you choose, as novaderrik said.

1st gen factory drum/drum does not have a prop valve, just a distribution block with warning light switch.

1st gen factory disc/drum has separate metering and proportioning valves, and the same distribution block as the drum/drum.

i am ignorant on the needs of a prop/metering valve on 4wldisc. maybe check out david pozzis site. or find a 2nd gen t/a 4wd and see what it has.

The drum master cylinder will hold about 10 psi to the calipers keeping them slightly clamped on the rotors. This will cause your pads to wear prematurley. The master needs to be changed. Depending on what calipers you have, will dictate what master you need to go with. If it is a stock set up, a 1" disc/ disc manual from a 67 vette would probably do the trick. If you want power, then go with the 1 1/8" master. If you are running any else ie c4 brakes or ls-1 calpers then the mc selection will change dramatically.

As for the proportioning with the 4 wheel disc set up, I would use the stock distribution block that your drum car came with and install an adjustable prop valve from wilwood, available from summit 39.99 on the rear line going to the back brakes. This will allow you to tune your set up.
hope this helps.
let me know what calipers front and rear and I will help you with the MC selection.

The ft.disc and calipers are from a 74 nova factory set-up,and the rear are from a 2000 S10 blazer factory aluminum caliper with a vented style rotor.What a combination huh.