I have a 58 Ford Courier with 68 LTD spindles and disc brakes, stock 9" drums in back. It stops fine but the pedal pushes hard. Dual disc/drum master cylinder with proportioning valve. I built it long ago, but I'm guessing the LTD had power brakes. Looking online the piston should be 2 5/16". They don't show 68 LTD with manual brakes/disc, but I look up a 73 Torino with manual and discs and those calipers are 3 1/16". Would that 3/4" diameter difference make the pedal hard? I have tried different bore master cylinders and other things and haven't gained much and now I'm thinking it is the caliper size. Any advice? Thanks in advance.
Let's start with; What is your brake pedal ratio? https://techtalk.mpbrakes.com/how-to-series/correctly-calculating-pedal-ratio
I used to have a booster on it and I had the opposite problem. Pedal went to the floor but would stop on a dime. That's when I learned about pedal ratios. That was 302 days. I have since installed a 390 and there isn't room for a booster, master cylinder almost touches the valve cover.
I have changed the master cylinder to the smallest one I could find at the time (several years ago and I don't remember the size) but I might try to go smaller if I can find one. As for the ratio, it is the stock, not power brake 58 Ford but I am going to check it out to see if can relocate the cylinder rod pin to help out. I know that makes a big difference. Crawling up under the dash with vintage air in the way is a problem for an old guy, but I think I can still fit, lol.
I just did some more checking. My pedal ratio is 6:1 so that should be fine. I really can't move the rod point up any more because of the return spring and a curve in the pedal. But, that ratio should be good for manual brakes. I tried to measure the MC bore from under the dash and it is 15/16" as near as I can tell. Maybe 1", but I think it is a tad smaller. I have ordered a caliper for a Torino (which I doubt will fit my 68 LTD brackets) and I am going to check that out. It has a 3 1/16" piston compared to what my LTDs should have (2 5/16"). I would think that would help my pedal pressure. Would dropping my MC from the 15/16" to 3/4" help that much? Thanks in advance.
The change from 15/16" to 3/4" is just a whisker of a change, right? Actually no! It's a reduction of just shy of 36%! 36% more travel for the same volume displacement, could be problematic. 36% more pressure for same input or 36% less input to achieve same pressure sounds most attractive, as long as there's enough pedal travel to achieve it. I'd suggest small steps! 7/8" will give a 13% change which will be noticeable. By way of comparison, I've dropped from 1 1/8" to 1", a reduction of 20%. This made the difference between feeling very unsafe as there was no real bite in the brakes, slowing down but not really braking, to almost being pressed to the screen! I'd see where the caliper swap gets you first. Chris
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