Join Date: Sep 1999
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Re: Master Brake
From a post from CJ-8/5.2Mag (I completed this upgrade recently along with 78 CJ large front discs and rear drums. Makes an huge difference):
Get a reman booster/master assembly at your local "Pep Boys" type parts house for a '68-'82 Corvette (usually $99-$140, after you turn in your Jeep booster for a core, a regular parts house with a good counterman may check that the booster core isn't the same and may not take it back!).
Order the firewall to booster braket from a '87-'94 YJ (without ABS)from the dealer (under $15) or get one from a wrecker, this fits the CJ firewall perfectly. Open up the 5/16" booster-side bracket holes slightly to fit the Corvette booster.('68-'76 boosters are std thread, 3/8"USS nuts. '77-'82 boosters have metric threads, 10MM. They are interchangeable as long as you use the matching master cylinder).
You will notice that the Corvette booster has a male 3/8" SAE fine thread rod instead of the eye that is used on the Jeep master cylinder or booster bracket rod. You will need to cut off the rod so it's about 4" long and thread it to 3/8" SAE with a die (cut off the small end of the rod that goes through the firewall if you are using the rod from the stock booster linkage). Use a connector nut available from Dorman products at your favorite parts store, or from a hardware store, for around $2.
Bolt the bracket to the firewall. Temporarily bolt the booster with the long rod attached, connect it to the brake pedal and check the pedal height. It should be about 1"-2" higher than the original power brake pedal, usually about even or slightly higher than the clutch pedal will work out perfectly. Shorten the rod slightly, if needed, to lower the pedal height. Extend by unthreading the rod out of the connector nut. Be sure that the threads go into the connector nut at least 1/2", bottomed out against the threads from the booster is best.
Once you are sure of the length, using red locktite, tighten the connector nut to the booster, and use a Jam nut on the pedal rod end for a tight connection. Install the booster to the firewall bracket, and brake pedal pin using a new cotterpin. Readjust the brake switch by pushing it against the pedal tab until the lights work properly. The brake lines swap front to rear on the master cylinder. The GM master front/rear cylinder ports are opposite of the Jeep ports but threads match the proper tubes. Bleed the brakes properly, and test drive, carefully. You will notice that the brake effort is extremly light and the Jeep stops better than it ever did stock!
The conversion works well because the dual diaphram booster, the larger (and cheaper to replace) 1 1/8" bore master cylinder, compatability with disc brakes and the added leverage from the brake pedal. The only drawback is the increased pedal height that a long legged driver may object to, but most people get used to it quickly.