Products to Compare (max of 3)
X
Compare These Parts
Talk to the Experts. Call 800.979.0122, 7am-10pm, everyday.
Since 1952
in
in
Talk to the Experts. Call 800.979.0122
Shop By
Support
Account
Street Race Truck More... The Toolbox

How to Test And Fix Spongy Brake Pedal

7/12/2016
Tags: Tech, Brakes
How to test your brake booster
91031430

After you’ve successfully bled your brake system, does your pedal continue to feel spongy or are you still not getting the performance you need out of your brakes? One of the first things you can check is the integrity of your booster and master cylinder.

*The valve on your booster where the vacuum line plugs in is a one-way valve and it’s the first thing to check.

*Next with the engine off, pump the brakes several times to remove any residual vacuum in the booster.

*Now push the brake pedal firmly down and hold pressure on the pedal, start the engine and when the vacuum reaches the booster the pedal should go down slightly. If it doesn’t move at all or if it goes down over an inch or more there is probable cause for concern.

*Next install a vacuum gauge in the line at the booster, start the engine and check the available vacuum. For full assist manufacture requirements vary between 17-22” of vacuum.

*When using a more radical lift cam with lower manifold vacuum supply, one option is to use a 12 volt vacuum pump available from Speedway under part number 91028146.

How to test a dual feed master cylinder
91031428

Note: This test will require a complete re-bleeding of the system due to the brake lines being removed.

  • First remove the brake lines from the master cylinder ports. Then block off the master cylinder brake line ports using the correct size inverted flare plugs or bolts. Dual feed master cylinders may have ports on both sides that need to have all four outlets plugged off.
  • Note the protruding male cone of the inverted flare seat in the master cylinder port is made of a soft material and can easily be damaged.
  • After all the ports have been plugged, apply constant pressure to the pedal, the pedal should be firm, and should not drop over time. If the pedal quickly becomes squishy there may be air in the master cylinder. You may need to bench bleed the master cylinder. If the pedal is firm and then drops over time under constant pressure, the master cylinder should be replaced.
Common pedal ratios

There are many variables that can come into play when determining what your pedal ratio should be. Input force, the master cylinder bore size, and of course the pedal ratio. The line pressure achieved is a direct result from each of these variables and every system will require an optimal line pressure. From our experience, on a typical street rod application, what our technicians typically recommend as an excellent starting point is a 6:1 ratio when using a 1" or 1 1/8" bore master cylinder, power or manual setup. Since pressure range outputs can vary, it’s a great idea to install a pressure gauge to verify what your maximum pressure achieved is.

Many of our customers experience spongy or hard brakes due to incorrect line pressures, which are caused by incorrectly matched components. Sometimes it's impossible to identify the problem until you have some data to work with. The brake pressure testing gauge we offer, part number 91001704 is a must have tool for anybody designing their own brake system. From our experience, typical line pressure in a panic stop can be upwards of 1200-1300 PSI, while routine pressures can be around 800 psi or even less on drum brakes.

Products Featured in this Article

Related Articles

Manual Brake Bleeding
by Jason Lubken - Posted in Tech
7/13/2016
Manual brake bleeding can be one of the most efficient ways to bleed the air out of your brake lines. Speedway Motors has created a guide to show you step-by-step how to manually bleed your brakes.
Brake Valve Guide: Metering, Residual, Proportioning and Combination
by Speedway Tech Team - Posted in Tech
10/13/2016
Learn about the different types of brake valves. Our guide covers Metering, Residual, Proportioning, and Combination valves to understand your brake system.
Brake Pads and Friction Surface
by Speedway Tech Team - Posted in Tech
7/18/2016
We offer a guide to follow when selecting a new set of brake pads for your race car. It's important to know the friction quality and pad size before selecting a new set of racing pads.
Bedding In Brake Pads - Learn How To Do It
by Jason Lubken - Posted in Tech
7/18/2016
Learn how to bed in or burnish your brake pads. Our quick guide and video will teach you the proper procedure to get the best performance out of your brakes.
Bench Bleed Master Cylinder - How To Guide
by Jason Lubken - Posted in Tech
7/13/2016
Learn how to bench bleed a new master cylinder. Removing the air before installation is critical. Our video tutorial will walk you through the process.
Braking Components - Selection and Design
by Jason Lubken - Posted in Tech
7/13/2016
Looking for a performance or custom brake set-up? Whether you're replacing components or building your brakes from scratch, you may wonder what size master cylinder or booster to use. No need to worry, just follow our handy guide.
Speedway Tech Talk - Disc Brake Set Up
by Tim Matthews - Posted in Videos
5/24/2016
We get a lot of questions about brake kits so Tim gives a brief overview of disc brake setups.
Brake System Diagram - Street Rod
9/19/2016
Use our Brake System diagram to help with your street rod brake system project. We also diagram both single flare and inverted double flare fittings for you.
1969-77 GM Brake Calipers
by Steve Lewis - Posted in Tech
11/1/2017
Steve explains the process of installing Speedway calipers.
Speedway Tech Talk - CPP Hydroboost Brake Systems
by Pat Orth - Posted in Tech
5/17/2017
Speedway Motors employee Pat O. talks about the CPP Hydroboost Brake System.
Error
X
Note
X
Ok