True Connections

We can all agree that one of the most important performance upgrades you can make on a Chevelle or El Camino is upgrading the braking power. This usually entails a complete disc brake changeover, but even simply adding a power brake booster to a non power car can make a world of difference. In 1964-1966 Chevrolet offered the option of a 9” diameter power brake booster, then in 1967-1972 they increased the size of the booster to 11”. These diameters were carefully determined to give the driver the best power assist and pedal feel in relation to the weight of the vehicle and available vacuum from the engine. A disturbing new trend is companies selling 7” and 8” boosters to customers claiming they will work. The problem with this is that the 7” booster was originally intended for a 2600 lb car such as a Chevette. Your average Chevelle weights around 3500 lbs. It comes down to the little booster not being able to keep up with the demand the vehicle is placing on it. It creates an unsafe situation where the pedal is unreasonably stiff and you may only get one good pump out of it since there is not enough vacuum on hand to supply the required pressures. So I ask what exactly is the point of that tiny booster? The only thing I can think of is if someone is using a big block with roller rockers which require tall valve covers, then you might have a clearance problem. But aside from that, please use a stock size booster, after all, don’t you want to protect your $30,000 investment. Converting a non power car to power brakes is fairly simple. The master cylinder is actuated by a pushrod that is held to the brake pedal with a clevis pin. Remove the pin and pushrod. Next, the master cylinder is held to the firewall by two studs, remove the nuts and pull the master forward. Many cars have enough slack in the hard lines to allow the master to sit further out but the correct way to do this is to replace the lines with the correct style. The next step is to place the booster on the four mounting studs on the firewall and bolt it on, then bolt the master cylinder to the booster making sure the pushrod length matches the length required for your master cylinder. There are only two lengths, the deep master has a hole approx 1.6” deep, while the shallow master merely has a dimple where the pushrod actuates the master cylinder. Back under the dash, the clevis and pin are going to attach to the lower hole on the pedal, but before you do, you need to adjust the clevis so the pedal will have 1/16” to ¼” free play between the pushrod and master cylinder. This can be difficult to determine with everything bolted together so the easiest way is to remove the pedal return spring and adjust the clevis so there is the correct free play between the pedal and the rubber stopper. The final step is to connect the booster to vacuum. This is accomplished with the booster check valve being connected with a 3/8” vacuum hose to a fitting installed in the intake port of the engine manifold. There should be an existing fitting behind the carburetor but will most likely need to be replaced with one that has the correct outlets on it for your application. In the following months we will be discussing the 1966 Chevelle and its options.