Power Drum/Drum 1" master 1 1/8" front wheel cyl 7/8" rear wheel cyl Muscle Car Brakes recommends updating the rears to 1". what is that going to do? (from their site) plus High Volume Wheel Cylinders for less padal pressure. http://www.musclecarbrakes.com/ i wonder what the bias is front/rear from the factory Cheers!
Increases the force on the rear shoes. Front and rear shoes will now have nearly equal force pushing them into the drum. If the front brake shoes are larger/wider, or of higher-friction material, the front brakes will still have more power than the rears. However, the rears will have more power than originally designed. The car will stop more quickly...but...if the rear brakes lock before the front brakes, you'll lose control.
I respectfully disagree!... 1" does not increase the force on the rear shoes. 7/8" does though. Call Booster Steve at Power Brake Booster Exchange (503-238-8882) he corrected me on this same question last year. I also thought 1" would create more pressure but after talking to him about this for 20 minutes, he finally convinced me I was wrong and that 7/8" cylinder gave more stopping power. I guess it would be like a garden hose or maybe even electrical current and gauge of wire...although I'm no electrical expert but it reminded me of electrical wire current flow. Buick Eric / Oregon :3gears:
If you are having a problem with the rears locking up prematurely then going to a LARGER rear cylinder will help this problem. If like many you have larger rear tires than front you need MORE pressure. If you do go the a larger diameter more than likely you will have to install a 10lb. residual valve to maintain a proper pedal height because of the larger capacity cylinder. Tom T.
Hydraulics: In a closed/static system, fluid pressure is the same in every part of the system. 1. Don't confuse pressure with force. I very carefully used the word "force" in my previous post. 2. Let's keep the math fairly simple. Let's say that you step on the brake, and you generate 500 psi, and you hold the pedal. Almost instantly, the fluid surges through the tubing, the brake valves (if used), the distribution block, the rubber hoses, and moves the pistons in the caliper or wheel cylinders. 3. Because you're holding the pedal, the system is now both closed and static--the rubber hoses expanded a little, the wheel cylinder seals and pistons moved outward, but there's 500 psi everywhere in the hydraulic system, except the reservoir, of course. 4. One-inch diameter wheel cylinders have .7854 square inches of surface area. Area = pi X 1/2 diameter (the radius) squared. 1 / 2 = .5. .5 squared is .25. .25 X 3.1416 = .7854. 500 psi acting on .7854 = 393 pounds of force pushing the shoe into the drum. 5. 7/8 diameter wheel cylinders have .6013 square inches of surface area. 7/8 = .875. .875 / 2 = .4375. .4375 squared = .1914. .1914 X 3.1416 = .6013 square inches. 500 psi X .6013 = 300 pounds of force pushing the shoe into the drum. 6. 1 1/8 diameter wheel cylinders have .994 square inches of surface area. 500 psi X .994 = 497 pounds of force pushing the shoes into the drums. 7. Given the same psi generated by the master cylinder, bigger wheel cylinders push the shoes harder, but require more fluid and therefore a lower brake pedal than smaller wheel cylinders. Because the larger wheel cylinders require more fluid flow, it will take a fraction-of-a-second longer for them to apply--the fluid has some friction flowing through the plumbing system. 8. This also applies to disc brakes--disc brake pads can be so small in comparison to drum brake shoes, because the huge caliper piston (by comparison to a drum-brake wheel cylinder piston) applies FAR more force to the pads. Is my logic flawed?
