Speedway Single Diaphragm Power Brake Booster, 7 Inch, Chromate Finish
Universal Fit, 3.70" Overall Thickness, 7" Outside Diameter, 3.38" x 3.38" Bolt Hole Pattern
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Single diaphragm boosters are compact for installation under floor or on firewall of almost any vehicle. Booster measures only 7" in diameter. Zinc chromate finish. The single diaphragm is usually used on lighter vehicles. In the heavier applications of 3000-3500 pounds or more we normally use the dual diaphragm boosters.
You will need full manifold vacuum available to the booster. Manufacturer requirements vary between 18 and 20 inches of vacuum. With radical cams there are many cases where there is a loss of the necessary vacuum and the only option is a 12 volt vacuum pump available from Speedway under part number 91028146.
- O.D. is 7" Length from mount surface to master cylinder mount surface is 3-5/8" (this does not include the shoulder that extends into the master cylinder)
- 3/8 x 24 thread pushrod that is 4" long from mount surface to end of the threads (pushrod nut included)
- 4 bolt mount pattern on 3-3/8" centers
- Mount bolts are 5/16 x 20 and 7/8" long and nuts are included
- Master cylinder mount studs are 3/8 x 18 and 1-1/16" long and 3-3/8" on center
Booster Tech Tip (GIF)
Learn more about selecting the proper brake booster for your vehicle by reading our tech article. Brake System Selection.
How to test your brake booster vacuum:
The valve where the vacuum line plugs in is a one way valve and is the first thing to check. Next with the car not running 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 you need 18-20” of vacuum available.
This booster accepts master cylinders designed for a boosted brake system that have 3-3/8” center to center mount pattern. Depending on the application Speedway offers 1” bore GM style master cylinders for the front disc and rear drum vehicles under part number 91031445 or for the four wheel disc applications we offer a 1-1/8” bore master cylinder under part number 91031440. We also carry several other options in chrome, polished aluminum, and performance versions from CPP.
Installation Note: Before installing the master cylinder onto the booster, you may need to make an adjustment. The pushrod on the brake booster should protrude 1/16" from the face of the booster to insure proper engagement with the master cylinder.
NotesLength from mount face to M.C. mount face is 3-5/8". Pushrod extends 4" from mount face and has 3/8"-24 threads. Mount bolts are 5/16"-20 x 7/8". M.C. mount studs are 3/8"-18 x 1-1/16".
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Q & A
After getting the control arms and drop spindles installed last time, we are dying to see what it looks like on the ground. Today we are working with the Speedway Deluxe Disc Brake Kit. Josh and Joe are on a roll!
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Tim explains the process of adjusting Buick Finned Drums to fit Speedway's self-energizing backing plate assembly.
So you've bleed your brakes, but you're still having trouble with that squishy pedal. If you're certain you have the air out of your brake lines; follow our guide to help check your master cylinder, booster, pedal ratios, and line pressures.
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.