What can Cause Spongy Brakes

After you’ve properly bled a brake system, does the brake pedal still feel spongy, or are your brakes not providing the necessary stopping power?

The integrity of your booster and master cylinder is among the first things you may inspect. The valve on your booster where the vacuum line connects is a one-way valve, and it should be checked first. Next, with the engine turned off, repeatedly pump the brakes to remove any leftover suction from the booster.

What can Cause Spongy Brakes

Now, depress the brake pedal firmly and maintain pressure on the pedal, then start the engine; when the vacuum reaches the booster, the pedal should go slightly downwards. If it does not move at all or falls more than an inch, there is likely cause for concern.

Next, attach a vacuum gauge to the booster’s vacuum line, start the engine, and measure the available vacuum. Vacuum requirements for full assist manufacturing range between 17 and 22 inches. When employing a cam with a more extreme lift and a lower manifold vacuum supply, a 12-volt vacuum pump.

How to test a master cylinder with dual reservoirs.

Due to the removal of the brake lines, this test will necessitate a complete re-bleed of the system.

Remove the brake lines from the master cylinder’s ports before proceeding. Then, obstruct the master cylinder brake line ports with inverted flare plugs or nuts of the appropriate size. Dual-feed master cylinders may contain ports on both sides that must be closed off simultaneously. Note that the projecting male cone of the inverted flare seat in the master cylinder port is comprised of a material that is readily damaged and constructed of a soft material.

Apply steady pressure to the pedal once all the ports have been put in; the pedal should be firm and not sag over time. If the pedal turns mushy abruptly, the master cylinder may have air. You may need to bleed the master cylinder on the bench. The master cylinder should be replaced if the pedal is initially firm and subsequently begins to sag with continual pressure.

Standard pedal ratios

Numerous aspects can be considered while calculating the optimal pedal ratio. Input force, the bore size of the master cylinder, and of course the pedal ratio. Each of these variables has a direct effect on the achieved line pressure, and every system requires an optimal line pressure. When employing a 1″ or 1 1/8″ bore master cylinder with a power or manual system, our specialists normally recommend a 6:1 ratio as a good starting point for a typical street rod application. Because pressure range outputs might vary, it is a good idea to install a pressure gauge to confirm the maximum pressure achieved.

Incorrect line pressures, which are the result of mismatched components, result in spongy or harsh brakes for many of our clients. Occasionally, it is impossible to detect the problem until sufficient data is collected. The brake pressure testing gauge is a must-have for anyone constructing their brake system. From experience, typical line pressure during a panic stop can exceed 1200-1300 PSI, although normal pressures on drum brakes can be as low as 800 psi or even less.