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1955-64 AFTERMARKET POWER BRAKE BOOSTER INSTALLATION AND ADJUSTMENT

1955-64 AFTERMARKET POWER BRAKE BOOSTER INSTALLATION AND ADJUSTMENT


WAftermarket power disc or drum brakes are perhaps the single most popular upgrade on a Classic 1955-64 Chevy. There are several things to consider when replacing a stock non-power master cylinder with an aftermarket power brake booster. Most aftermarket brake boosters will bolt up to the stock firewall without any modificationsb,ut if everything is not adjusted properly the booster will not work correctly, giving you poor braking action. In this article we will show you how to properly install an aftermarket booster on your Classic and make all the necessary adjustments


Image #1: When installing an aftermarket brake booster on a 1955 to 1964, PIN 57-157863-1 booster and mounting brackets bolt directly to the firewall us ing the four studs that mounted the original non-power brake master cylinder. If your 1955-58 car had the original Treadle-Vac power brakes, the brake pedal assembly will need to be changed to a non-power brake pedal assembly. The power brake pedal differs in shape and will not give proper pedal leverage or travel. The mounting brackets that bolt to the back of the booster give the booster a slight upward angle giving increased pedal travel. There is a 3" long pushrod and clevis that connects to the stock non-power brake pedal. This is adjustable so that the brake pedal height can be set.

Image #2: The reason for mounting the booster at an angle is to relocate the attaching point for the pushrod lower on the brake pedal swing arm. On a non-power brake pedal swing arm the 3/8" hole for the master cylinder pushrod is 2" down from the pivot point of the pedal. When installing a new booster, a new 3/8" hole must be drilled in the brake pedal swing arm l " lower than the stock hole. This will change the brake pedal ratio from 5.5 tol to 3.6 to 1. The booster will not operate properly unless the hole is relocated in this manner. The clevis is held to the brake pedal swing arm with a pin and cotter pin that is included in the booster kit. Adjust the booster pushrod so that the brake pedal swing arm is 1/16" below the brake pedal bumper PIN 57-131189-1.

Image #3: The master cylinder that is used on the power brake booster has a shallow dimple in the rear of the piston. A non­ power master cylinder has a l " deep hole in the rear of the piston. When the master cylinder is installed on the booster, the pushrod from the booster should just rest on the dimple on the master cylinder with no pressure on the piston. If the pushrod from the booster is adjusted out too far and depresses the piston any at all, the residual valves in the master cylinder will not allow the brakes to bleed back when the pedal is at rest and the brakes will hydraulically lock up. The end result: your car will not roll!

If a non-power master cylinder is installed (with the l" deep piston hole) you may get no brakes at all since the booster pushrod will not reach and activate the master cylinder piston.

Image #4: The pushrod on the front of the power brake booster is adjustable. By holding the nut on the booster by hand and turning the center pushrod, it may be lengthened or shortened to ac hieve the proper clearance

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