Hello Gatorjaws,
On most modern passenger cars the rear brakes activate before the fronts, then the fronts kick in and do most of the braking.
The sequence is...............initial pedal travel fills all cylinders, front and rear, moving the rear shoes to the drums and the brake pads to the front discs. As pedal pressure increases, slight rear braking occurs, next the front brakes kick in and do most of the braking. The rear brakes will lock up eventually only under the most severe braking and usuallyafter the front brakes have locked up.
If the rear brake adjustment is loose, it take more initial pedal travel to move the shoes into position. Braking by front and rears remains functionally the same. No real breaking occurs until all the friction pads are next to their drums or their rotors.
The internals of the master cylinder are designed with two sequential stages. The master cylinder controls when each axle does its braking. Some cars have different bore diameters in the master cylinder to vary pressure in the front and rear circuits . Most master cylinders are designed to lightly pressurize the rear axle first then the front axle. Different diameters of the pistons in the front calipers and the rear brake cylinders also regulate the amount of braking force at each axle. In addition the square inch area of the brake friction surfaces, front and rear, also determines which axle does more or less braking.
On the later W113 cars a rear proportioning valve was added to tweek braking characteristics.
On race cars a main proportioning valve or dual master cylinders can be adjusted to change braking characteristics for variable road surfaces.
