The braking system, without a doubt, contains your car's most important components. Nothing else matters without good brakes. Steering is important, but if the steering breaks, then the brakes will bring you to a stop. If the brakes go, all the steering will do is help you point your hot rod in the direction of the softest object you can find.
Last month we went over some of the basics of braking, explaining the different types of valves and master cylinders, and answering some of the more frequently asked questions. This time we once again turned to some of the braking experts and picked their brains on how to properly set up your system and help diagnose some of the simple problems that seem to pop up, preventing the braking system from performing at its best. They had the answers to all of our questions, and even some we didn't even know we needed to ask.
Brake Troubleshooting Guide Soft Spongy PedalA Defective Master CylinderSome fluid will bypass the seals under pressure if the bore in the master cylinder is pitted or the rubber seals have decreased in size, giving a lower pressure to the wheels and a softer, spongier brake pedal.
To test for this condition, remove the brake lines from the master cylinder and plug the outlets (obtain outlet plugs from a local auto parts store). When you apply the brake pedal, it should be high and firm. If it is spongy or slowly goes down, then either the bore is pitted or the rubber seals are bad.
No Residual Valves To Rear DrumsFor drum brakes to function correctly, there needs to be a 10lb residual pressure valve in the system. This residual valve will maintain pressure on the drum brakes to counter the spring pressure in the system. This keeps the shoes out close to the drum, giving a higher, firmer pedal. Every time you step on the pedal without the residual valve, all the fluid goes to moving the shoes out before drum contact.
If you remove the lines that go into the master cylinder and look at the brass seat in the outlet with a flashlight, you should be able to see the little black rubber check valve under the seat. You will need to install an inline 10lb valve if your master does not have one. Use a straightened paper clip to check for a residual valve. Insert the clip into the center of the brass seat; there is a residual valve present if it meets a restriction within 1/2-inch.
Air in the SystemThis is obvious, but sometimes all the air has not been removed after bleeding. One reason is the incorrect orientation of the bleeder screws in the wheel cylinders. A pocket of air will always remain if the screw is not at the highest point on the cylinder chamber. Check the screw orientation.
Master Cylinder Piston Diameter is Too SmallYou will experience a long pedal travel if the diameter of your master cylinder piston is smaller than required by the wheel system volume requirements. Determine what the original master cylinder bore diameter was and replace the master if it's too small. Remember, we're working with old cars and the master cylinder most likely has been replaced, and maybe incorrectly, by a previous owner.
Incorrect Booster Pin LengthThis is for power brakes only. You will get a spongy pedal if the pin that goes from the booster to the master is too short. The pin should be 1/64-inch from touching the master cylinder piston with the master cylinder mounted on the booster. Too long a travel before engaging the master cylinder gives a soft pedal feel.
Drum Brake Wheel Cylinders Too LargeIf the original drums have been upgraded to a larger drum system, then the fluid volume requirements have increased. Using the original master could lead to a long pedal travel with a spongy pedal feel.