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Better Braking Upgrade: Jeep Power Brake Boosters

Posted in How To: Transmission Drivetrain on August 1, 2011
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As much fun as it is to go wheeling, it’s even more fun to be able to stop your 4x4, especially on a cliff. With vehicle upgrades and homebuilt designs, we often don’t think of improving the bake system until it’s too late. In fact, we’ve seen guys put 44-inch tires on a 1⁄2-ton truck with stock brakes and then wonder why they can’t slow their ride down anymore.

It’s a simple fact that more weight and rotational mass (bigger and heavier tires) require more braking power. A system designed for 29s just won’t cut it when 35s are installed, but there are many brake upgrades you can do to improve the system’s efficiency. Adding disc brakes is a popular conversion, as is adding large brakes and rotors. But if you’re stuck with a manual brake system instead of power, you’re still just flogging the dog in an attempt to stop securely.

We recently upgraded our Ultimate A1, the Jeep we built for the 2001 Ultimate Adventure (Oct. ’01), from manual four-wheel discs to full-on power brakes using a dual-diaphragm Navajo Brake Booster. The Navajo design is from the mind of Harold Off of Off Again 4x4 in Farmington, New Mexico. He set up our most recent Jeep as well, the UA CJ-17 from the 2010 Ultimate Adventure, and we are super-pleased with how both rides stop on a dime. Check out how easy it is and see if you don’t need a brake upgrade as well.

Our original brake system didn’t function as well as it could with our increase in tire size. We hoped the addition of a power booster would give our old legs more braking action with less effort.

The master cylinder needs to be drained and removed from the stock location. We had used a stock-style ’75 CJ master on this setup, which powers the four-wheel discs on our Currie Dana 60 axles. It works fine, but bigger tires take more power to stop.

With the old one off, the difference is obvious between a manual (left) and power (right) master. The manual master uses a long push rod from the pedal to extend into the master cylinder, which has a corresponding deep piston recess. The power master has a shallow recess that takes a short rod off the booster, and a different rod from the pedal to the booster.

Nothing on a custom ride is bolt-in, but a stock Jeep would be. We had our two-bolt manual master fitted directly to the firewall reinforcing plate. While the two master cylinders have the same pattern, the bracket between the new booster and firewall needed to be fitted. After four holes are drilled in proper alignment, the booster and bracket can be bolted on.

The new power master bolts to the dual-diaphragm Navajo booster, and then is bled. Make sure you bench-bleed the master first, then install it and bleed again. Install and adjust the push rod from the pedal into the booster, then bleed the system again. If the brakes are mushy, you have air trapped somewhere in the system and it needs to be evacuated.

The booster requires a source of manifold vacuum to function properly, although it will work without it in emergencies. We found an unused vacuum port on the back of our engine that simply needed a 1⁄4-inch pipe fitting to a nipple. Make sure the hose is of good quality and the hose clamps are worm drive instead of the stock pinch style.

The finished system still fits under the hood thanks to the small-diameter, dual-diaphragm Navajo booster. The stock-sized lines fit into the new master. After final bleeding and brake testing, a simple adjustment to the brake proportioning valve was all that was needed.


Off Again 4x4
Farmington, NM 87401

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