Step 8: Make the Brakes Trustworthy

CJ brakes stop the Jeep fine — until they do not. The brake system on a CJ is simple and serviceable, but it was designed around stock tire sizes and it degrades in ways that are not always obvious until you actually need to stop hard. Treat the entire brake system as unknown until you have personally inspected every component.

Inspect everything

Pull all four wheels and do a complete brake inspection. Look at:

• Front brake pads or shoes — measure remaining thickness
• Rear brake drums and shoes — check for scoring, glazing, and shoe thickness
• Wheel cylinders at the rear — look for any wetness or seeping fluid around the boot
• Front calipers if disc equipped — check for leaking and piston movement
• Brake lines throughout the Jeep — look for rust, kinking, and improvised repairs
• Rubber flex hoses at each corner — look for external cracking and swelling
• Master cylinder — check the fluid level and look for leaking at the firewall
• Brake booster if equipped — check the vacuum line and test the boost with the engine off (pedal should firm up after several pumps)

Replace anything that is suspect. Brake components are not the place to leave marginal parts in service.

The master cylinder bore size

A common mistake is installing a larger-bore master cylinder in the belief that it will improve braking. It does the opposite. A master cylinder with a larger bore displaces more fluid per inch of pedal travel, which means more pedal movement is required to generate the same line pressure. The correct master cylinder bore must be matched to the total piston area of the calipers and wheel cylinders it serves. If you are running stock brake components, use a stock master cylinder. If you have upgraded to aftermarket calipers, the master cylinder selection needs to match them.

Bigger tires and braking

If the Jeep has been lifted and is running larger tires, understand that the braking system was not designed for that configuration. Larger tires increase rotational inertia, increase the leverage distance between the contact patch and the wheel hub, and add unsprung weight. All of these factors increase the workload on the brakes. A system that stops adequately with 31 inch tires will require more pedal effort and show more fade with 33 inch tires. With 35 inch tires the difference is significant.

If the Jeep is running 33 inch tires or larger, evaluate whether the brake system needs to be upgraded to match. Upgraded front brake calipers and a rear disc conversion are both well-documented and well-supported modifications for CJs running larger tires.