Hey guys, I'm building my wife her first "old car," a 1957 Ford wagon. We're converting over to discs on all four wheels and I have a question about this master cylinder and proportioning valve they gave me. I'm used to seeing 4 wheel disc brake master cylinders with equal sized reservoirs so I'm thinking this is the wrong master cylinder, do you agree? I'm going to call them and ask about the m/c but I want to know what I'm talking about so my real question is about that proportioning valve they sent. They said I didn't need one but I insisted so they threw this one in for free. I've done many disc swaps but I've never plumbed one like this. The rear port I usually use is capped off and they want me to plumb the rear brakes off of the side port. There is also no metering valve stem off the front of the valve or a warning switch. Is this an actual proportioning valve or just a fancy looking tee? I'm trying to build the safest car I can for her and I'm willing to pay for the correct parts. Any suggestions before I call them? Cheers, Art.
The master cylinder and prop valve look like late '60s/'70s Ford disc/drum components. I would definitely use a disc/disc master, whether Corvette style or stock '90s-up Ford Crown Vic/Lincoln Town Car, etc. I would only use an adjustable proportioning valve on any custom brake system, as factory fixed-value valves are designed and tested for a particular vehicle/axle weight, wheel base, engine size etc. Metering was used on and off throughout the late '60s-'80s on disc/drum only, so you don't want or need it on a disc/disc system.
That's what's called a "Combination Valve" like the kind used in Ford and Chrysler disc/drum systems. Generally it proportions front 70/rear 30 and meters the rear brakes to activate first to remove slack. If you have a failure in one of the circuits, it activates a warning light switch, which on yours is capped off.
The master cylinder may be fine; yes, different sized reservoirs is typical of disc/drum brakes, but the critical difference is the drum half of the circuit has a residual pressure check valve installed, none for the disc half. If the master was assembled without this valve in both ports, it's fine. I'll agree that the 'proportioning valve' they sent you is wrong as noted above. Now, as to whether or not you need one is hard to say. Probably not, but Wilwood (and others) make adjustable ones, that's what you want in a non-stock application.
if the port on the back of the porpotioning valve is set for a pipe then its a drum brake unit as thats were the buildup/limiting valve is located and the fluid goes thru it to the pipe , on a disc /disc unit they plug it off as the brakes will equally see pressure rise ( as not to lock up the brakes ) and is not as quick due to the flow rate . look on the unit for numbers as they will have a ID number on them ( single digit with cv in front of it then google that number as the industry is pretty standardized on numbers ) as for the master the bore size is what dictates how much fluid you put to the brakes not the resivour size ) you can have small res and a large bore on both sides and the brakes work . the purpose is to not have to check the fluid all the time as the shoes /pads wear
Thanks everyone, you all make a lot of sense. Stimpy, what you wrote about the rear port being plugged off tells me it's ok to use with my disc/disc set up. I figure I'll start with what I have and if I don't like it I will try without it or switch to an adjustable Wilwood. Crazy Steve, I'll check for a residual pressure valve in the rear m/c port. I still think I want an equal chamber m/c though. I'm concerned about running the small chamber dry as the rear pads wear and the piston moves outward. Thanks for the help, guys.
that combo valve has a shuttle valve in side that balances the fluid flow but if you run larger diameter tires on the rear , yes put a adj one on it to help prevent premature lock up . as for the master , I doubt you will empty the pot before the pads hit the rotors . the take up on a disc caliper is not a much as everyone think it its as the pad only moves about .020 on application vs the 1/4" or more of a drum wheel cylinder and the area is almost equal .
Gotcha. That makes sense too, Stimpy. Front and rear tires are the same size so that helps. And understood on the master cylinder reservoir size. Sounds like I'm good to start plumbing this thing as is.
It's too late, but I'll check in anyway. As I have said before, based on very personal experience, that booster is crap. The best braking systems I have built revolved around a Stock pedal-booster-master assy, matched to the Front brakes. Not knowing what brakes you are running, I cannot advise much more than the above. Do beware, the aftermarket does NOT expect you to drive this car, and will tell you whatever they think you want to hear, as I also know from still more personal experience. I know people all tell you that they drive their cars, but when I owned my '38 Chevy, it was the ONLY car I owned for two years, in Chicago. If I wanted to go somewhere, I took that Chevy. If it snowed 20 inches, I cleared off the windows of that Chevy. The braking system on that car?? M-II front brakes, allied to a M-II pedal - booster - master. The proportioning was done by juggling wheel cylinder sizing. Worked a treat, stopped beautifully. Cosmo
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