To recap (if anyone cares) I have a 63 Olds Dynamic 88 I bought back in september. The stock booster was shot, and I wanted to convert to dual master cylinder anyway. So, I got a Demoter Universal 8" booster and corvette style dual master for drum/drum setups. I replaced or rebuilt every component from the booster to the wheel cylinders including lines and hoses. The booster bolted right into the stock location and after modifying the clevis a bit, connected to the pedal just fine. I had virtually no brakes. the rear would lock up (which I later found out was a contaminated shoe), but I had a very stiff pedal with almost no pressure being applied to the drums. I finally had a friend come take a look as I was at my wit's end. After looking at a few things, he got under the dash and measured the brake pedal throw, and the position of the pushrod and explained the concept of pedal ratio to me. Essentially, the booster in the stock position on my car is only getting about 2.75 to 1, most more modern brake systems need about 5 to 1 or better. So with the help of a modified relocation bracket from speedway (for a 58-64 chevy), and some modifying of the brake pedal, I now have a pedal ratio of about 5.5 to 1 and I've got brakes! It only took about 2 months of weekends. Onto the next task! Cheers- geoff
Pedal leverage I think this is overlooked often Leverage,pedal angle, pedal height, pivot point. I tore my hair out for some time trying to cure poor brakes & this was the issue Gene in Mn
I feel your pain! Same thing holds true for clutch pedals. There is a ratio, 6 to 1 if I recall correctly, which needs to be maintained. There is also a way to calculate it but I cannot remember that. I just recall not being able to push my clutch in after getting everything installed. Pulled it all out and redid it with that ratio in mind and all is good.
Thanks for the guide. I was going to add an 70's Camaro master cylinder and booster in place of the existing F100 setup. I can measure the Ford F100 as I do have it but the Camaro I don't. I figure that will be my next challenge then unless somebody has this info or know where I can look easily...
RESEARCH, RESEARCH, RESEARCH. THERE IS A LOT OF INFO AVAILABLE IF YOUR WILLING TO LOOK. DO NOT GO BY SOMEONES OPINION. I LEARNED ALONG TIME AGO, WHEN YOU ASK SOMEONE A QUESTION, AND THEY START WITH " I HEARD, OR I THINK, " JUST WALK AWAY.
It turns out my F100 pedal has a ratio of 6.5 :1 I read that Camaro's around the era of my m/c and booster run approx. I had one of these disc/drum units fitted and basically could not pull my vehicle up except slowly, but hopeless in a emergency situation... I read this comment below which got me wondering. Whether your vehicle has power or manual brakes, pedal ratio is important. If you are experiencing a hard pedal you should check your pedal ratio if you have converted from the vehicle’s OE set up. As a general rule, your pedal ratio should not exceed 6:1 for manual brakes with a 1” bore master cylinder and 4:1 for power brakes with a 1-1/8” bore master. That just confused me more as I come from a F100 manual 1 1/8" bore m/c without booster with a pedal ratio of 6.5:1 and now have a 1" boosted m/c with the same ratio. My front brakes are Dakota and rears are 1964 Galaxie drums. My current booster and m/c looks like this below. Can anybody see what needs to be corrected if anything???
Typical non power 50-60’s drum brake car had a 3/4 or 7/8” bore M/C and a 5-1 or 6-1 pedal ratio. Add power to this and throw yourself thru the windshield so power went to a 1” M/C. Add front discs and a 1-1/8” M/C was added or a 4-1 pedal ratio was used. As for rear ends with drums if changing from a power brake car to a non-power brake car go to a smaller wheel cylinder by a 1/16 to 1/8”. Question like this are what Wilwood and others ask when you are asking for advice on what to purchase... if no questions are asked.... go somewhere else.
Well it sounds like I am close to having things right. I think I just need to shorten up my pedal ratio as I seem to have more than the required travel and getting pretty close to the floor. I read 2" floor clearance is suggested but no rule applies...
Re-drilling and repositioning the pedal will change the ratio, but the booster would have to be raised or lowered to keep the push rod travel straight, not angled.
The most important item to check when installing a dual master cylinder is full master travel before the pedal bottoms out, to benefit the safety advantage.
It's not rocket science, is it? I learned pedal ratio basics in the first grade, when I tried to teeter-totter with Blair Cavanaugh. By the time he was in the third grade we called him "Blair the Blimp". We were not a kinder, gentler nation at the time, and "politically correct" was not a mandate.
Sorry, been out of the loop for a couple days. Here's the link to the bracket kit. I cobbled together parts from their linkage, and made a new pushrod running straight through the firewall to the pedal arm at the new location. https://www.speedwaymotors.com/1955-1964-Chevy-Power-Brake-Booster-Bracket-Passenger-Cars,8888.html
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