Vacuum Brake Booster


One sideAlan Haley mentioned the device shown in the photos here, on the CJ-3B Bulletin Board: "My '58 3B has a device tubed in between the master cylinder and the brakes that seems to run off the vacuum of the engine. I assume that it is a power brake system of some kind. The device has a drum about 10 inches in diameter and four inches thick shaped like a discus. It is not in my manual anyplace and I cannot even find a reference to it in Chilton's. Does anyone know anything about these things or was it something that a former owner was experimenting with? What would happen if I bypassed it according to the Jeep manual diagrams?"
Bart McNeil spotted the booster in the "Special Equipment and Accessories" section of the CJ-3B Parts List: "Apparently as the vacuum powered brake booster was offered as an accessory early on in CJ-3B production. It is the last accessory listed in the 1956 Willys Motors Parts List:


Part No. 907996 Kit, power brake booster (Hydravac)....1 (Components to be obtained from Bendix Corp., or local dealers)."

The other sideTom Erichsen responded, "My '58 CJ-3B also has a brake vacuum assist mounted on the front left wheel well. It has helped improve my 9" brakes, but I recently added 11" brakes on the front axle only. The braking is 50% better and I am planning to add 11" on the back axle as well. My brake vacuum is still working and does not require a lot of pedal force."

Joel Kamunen likes the idea of the booster: "Your vacuum boost system was probably put on by sombody who wasn't pleased with the original brakes. The vacuum boost would be a great way to improve your 9" braking. If it seems to work, leave it as the original 9" brakes are inadequate for today's highways. There is a fellow in Australia who modified his 3B braking system using a General Motors unit and said that he was quite pleased with it. Its a good alternative to doing the 11" brake conversion." A new brake booster with a two chamber master cylinder is available from C.H. Topping & Co. It looks good to me but I haven't checked on the price yet. It may be an alternative to 11" brake conversion or It may be a good idea to add to an 11" brake conversion as the dual master cylinder is a great safety feature. Their phone number is (562) 432-0901."

Chuck Crowder thinks it isn't necessary: "I also have a '58 which had a vacuum booster. It was in terrible shape and I couldn't parts to repair it. The local shops couldn't even identify it. I removed it and re-tubed according to the original and it works fine. As stated by others, you will have to apply more pressure to the pedal without it."

Jim Sammons cautions, "Vacuum assisted brakes are nice, but remember they are not a substitute for adequate sized brakes. The same amount of heat will still build up in those 9-inch brakes when you apply them. All the vacuum assist does is give your leg a break. Of course it makes your brakes feel better 'cause you don't have to push as hard to get it to stop. But don't let that fool you, when you pull the wheels off you'll still have 9-inch brakes."

See also Tech Tips on other Brake Upgrades and a Disk Brakes Conversion.

Return to the CJ-3B Tech Tips page.

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Last updated 27 November 1999 by Derek Redmond redmond@cj3b.info
All content not credited and previously copyright, is copyright Derek Redmond