I hear that one change to make on an all drum brake system is to switch from a single pot reservoir to a dual reservoir master cylinder, in case of total system failure. I want to do this on my 61 Comet and want to know what other master cylinder is a direct bolt on? My current master cylinder has a 2 bolt pattern. I am currently running stock 13 inch steel rims. If I decide to go to a disc front system, with drum on the rear, what master cylinder will work for both? Not afraid to run drums all around until I upgrade to disc because I have all new lines and brake hardware, but don't want to but a new master if I upgrade.
You can change to a dual master cylinder, or you can make sure the brake system is in tip top shape, and use a single. either way there is some risk...it's an old car...anything can happen. Dual cylinders came into general use around 1967, it's pretty common to use one from that year car of the same model, and it might fit ok and work ok. Be sure the pedal travel is correct. If the dual system is working properly, you can open a bleeder valve at one brake, push the pedal, and it will not go all the way to the floor. If it does go to the floor, then the dual system is not working right, and you might as well just have a single MC. when it's time to do the disc brake upgrade, you might need a different MC...they don't really cost much, so you can buy a new one at that time.
A lot of the modern (last 10 years or so) masters have two fill lids, but are pretty much one cavity. If you loose a brake line, you only get maybe one more stop before the brakes are gone as well. If your current lines and hoses are in great shape, and your master is OK, I would wait until you do a disc upgrade before you replace the master and the lines, because the disc will likely need a larger reservoir then the drum brakes, and changing from a single reservoir to a dual reservoir will require the addition of a proportioning valve and changing or moving at least some brake lines. Gene
Just did this on my daughters 65' Falcon. Used a 67' mustang drum/drum master. Was a direct bolt on but had to use the original push rod. Making the new lines to separate the front from back was not a problem. If you search for mustang brake conversion there were some good info out there
Do you know the difference between a drum/ drum, disk/drum, disk /disk master cylinder? It's The built in residual pressure valve. The drum/drum has one for front circuit & one for the rear circuit. The disk/drum has only one for the rear. The disk,disk has none. They are removable too. Way back when rebuilding the master cylinder on the bench in the shop a was common practice the kits included new RP valves.
The RPV is one difference. Another is the reservoir size...disk brakes move fluid from the master to the caliper as the pads wear, so they need a larger reservoir.
I figured I had worded that in a way that is not easy to understand....oh well. As the pads wear, the caliper piston has to extend further. This requires more fluid to be in the caliper. The fluid comes from the master cylinder, and lowers the level in the reservoir. This is a slow process, one you won't notice if you check and "top up" the MC often. Normal folks don't do that, so car makers put a much larger reservoir on the disk brake side of a disk/drum master cylinder.This lets the fluid level slowly go down, but not so far that it gets empty, when the pads are completely worn out. I'm pretty sure you know this already, but some guys might not.
This is a pretty easy swap. Just run a single line to the rear, plug the rear port on the junction block. I forget if the Falcon by '65 still had the brake light switch on the master. This can be plumbed into the rear line with a 3/16 x 3/16 x 1/8 NPT tee.
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