Dunno why I bother sometimes . . . but has anyone ever put a disc master cylinder with drum brakes all the way around? I went to a dual master setup, but one side is drum, one is disc . . . I'm thinking I'll need a proportioning valve when it's all said and done, but not for sure. Everything I've read is the disc brakes need more fluid volume, so I'm thinking maybe it'll use less with the drum? Anyone do this before? I'm into this for $20 for the master so far . . . it's a manual one, but like I said, it's for disc/drum setup. Hmm. (This is on a 1962 Buick Special Deluxe -- going from single master setup to a dual 1981 Ford Granada one. It has to have passenger exits on brake lines.)
Let me clarify -- I have DRUMS all the way around on the car . . . bought Kanter rebuild and done them (well, all but rear so far . . . but that's another story). I have a DISC/DRUM master cylinder and I'm worried that the brakes will not work right . . . Yea . . . this backyard engineering stuff is fun . . . no wonder Baer brakes gets $$$$ for their crap.
Here is what I found out, take it for what it's worth. Stock drum brake master cylinders have check valves. Disc masters that are mounted above the calipers don't. If you use a disc master with drums you need a 10 lb. check valve in line on the master. I added a willwood 10lb check valve to my brakes and I couldn't get the fucker to quit leaking. Apparently the SSBC check valve is better quality. I have not got one yet. If you don't run a check valve your brakes will be soft, the drums need more fluid volume and pressure than the discs do to actuate the brake. However, I'm probably going to run mine with out the check until I upgrade to discs. The drums work the pedal just goes to the floor.
My wagon has 8 lugs all the way around (1963), and when I got it, the first thing I did was swap in a dual master. I used one from a 67 chevy pickup, with the "big drums" (6 lug style) on it. they had pretty substantial wheel cylinders on them, so I figured it was about right-it works perfect! the cylinders on the front are an inch and 1/8, the rears are 1 inchers. no prop valves, no residual valves, pedal is nice and firm (non power) and best of all, the rod to the pedal took about 30 seconds of modification to make it work ( non power masters have a little clip to hold the rod in, and I had to depress the plunger in the back of the master a tiny bit to make the clip fit in it, and take about a 32nd of steel off the rod itself to make sure the plunger was not going to be applying the brakes all the time) overall, the line and fitting work took the longest of the entire set up. we just ran the rear line with a coupler to the master, blocked off that port with a plug from a random brake kit (yes,safety brigade, it was FOR plugging lines) and ran the stock line to the rear port, after changing the fitting to the correct size. cakewalk. don't overcomplicate it, and it will work like gangbusters. funny thing is, the car stops about 10 times better than before, and the old master worked and was not leaking. I think the truck master has better pressures, so the set up has a little better grab. total cost involved...probably 100 bucks.
Yes I've used a disc/drum master with 4 whl drums. The fronts come on too fast and the rears always need to be adjusted up manually. The self adjusters aren't activated because of the fronts coming on so quick. I did this with a completely matching 74 Nova drum system with a Cutlass disc/drum master. If the master you have can be taken back do it and get a master from a 4 whl drum car you'll be happier
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