A fully functioning brake system requires three scientific principles to work in tandem to stop your Pontiac: Friction, leverage, and hydraulics. We've gone over the friction components in Parts I and II, so in this final installment we will discuss leverage and hydraulics.
Pedal Leverage Ratio
A brake system uses increased leverage to multiply your pedal effort so that the correct pressure can be sent through the hydraulic system to activate the calipers and generate friction with the pads on the rotors.
The brake pedal is suspended from its pivot point via a long steel bracket. The attachment point of the master cylinder pushrod is mounted on the same bracket, but is much closer to the pivot point than is the brake pedal. When you press the pedal, the mechanical advantage results in less required foot pressure to activate the brakes.
Here's is an illustration...
Here's is an illustration of how leverage is applied to the braking system. The distance from the pivot point of the brake-pedal bracket to the center of the pedal itself (A) is much longer than the distance from the pivot point to the master-cylinder pushrod-attachment point (B). The mechanical advantage at the brake pedal end results in reduced effort to apply the brakes.
The pedal-leverage ratio is determined by dividing the length from the pivot point to the center of the pedal by the length of the pivot point to the master cylinder pushrod mounting point. Typical Pontiac brake pedal ratios range from about 3.5:1 to 5:1 for power-brake cars of the '60s up to the '70s, and up to about 7:1 for manual-brake cars, which means that the pressure that you exert when you step on the brake pedal is multiplied from 3.5 to 7 times at the master cylinder, depending upon the vehicle model brake-system type. This ratio is built into your existing factory setup, and most aftermarket braking systems designed for bolt-in installations will not require modification.
However, Pontiacs up to the early '70s usually have two holes in the brake pedal bracket-one for power brakes and another for non-power. If you are upgrading to power brakes from non-power, you may have to move the pushrod from the upper hole to the lower to decrease the pedal ratio to work better with the new power brakes.
Manual brake systems rely solely on leverage to send fluid from the master cylinder to the calipers and/or wheel cylinders. They are normally found on older cars with drum brakes on all four corners, because drums require less line pressure than disc brakes. Pontiac did, however, offer manual disc/drum systems on certain models from the late-'60s to the mid-'70s.
These are the basic components...
These are the basic components of a dual-circuit master cylinder. A primary piston provides fluid to the rear brakes; a secondary piston provides to the front brakes via fluid ports. The front and rear circuits of the unit are completely separate to maintain safe braking pressure at one axle should the other develop a leak.
Currently, there are aftermarket manual-disc- brake upgrade systems available for street use, but many people complain about the increased pedal effort needed. On the racetrack it's a different story, as many race cars run manual brakes because they offer the driver excellent feedback through the pedal-something a road racer may be looking for going hot into a brake zone.
If your vintage Pontiac came with drums and no power-assist, companies like Master Power Brakes sell complete all-new front disc or four-wheel disc-brake conversions.
To reduce the required pedal pressure in stock and most aftermarket applications, the brake booster, which is mounted on the firewall and is directly connected to the pedal, augments the provided pedal leverage via engine vacuum and atmospheric pressure. If your Pontiac has a radical cam that provides a low vacuum signal, the brake booster, which requires 18 inches of vacuum, may not work properly. Master Power Brakes has an electric vacuum pump that can solve the problem.
An alternative is a hydroboost kit from Hydratech (hydratechbraking.com). It employs hydraulic pressure from the power steering pump instead, making the engine's vacuum signal inconsequential for braking.