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Jeep Brake Boost Options

Posted in How To: Suspension Brakes on June 4, 2018
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Modern factory brake systems are designed to provide some type of assist, helping the driver provide solid braking performance without causing his or her leg to go numb while bearing down on the pedal. However, when building a custom rig or dealing with vehicle modifications, there may be a time where one needs to replace the existing boosted master cylinder setup and change to something different. This could be from a desire to change the means of brake boosting or wanting to eliminate the brake boost function for simplicity and reliability. Another reason could be the lack of space for a large booster due to an engine swap or other space constraints.

It’s useful to note that going to larger brake pistons at the axles means they require greater fluid flow from the master to function properly. Increasing the master cylinder bore size can provide greater fluid and keep the pedal stroke short, but you lose mechanical advantage as you increase the master bore size. For a given push of the brake pedal, a smaller bore master will provide more hydraulic pressure out at the wheels, while a larger bore delivers more fluid to the brakes but at lower pressure.

We’ve seen cases where the stock vacuum booster was removed from the brake system, leaving a purely manual brake master on the vehicle. Where there has been room, or the brake master was mounted higher than normal, we’ve also seen fabricators extend the length of the brake pedal to increase mechanical advantage provided by the pedal pressure. Of course, the pedal movement under braking will also increase by a proportional amount, so that has to be taken into account as well.

There are alternative options to running the typical large vacuum-assist booster. These include smaller aftermarket boost systems, hydraulic-assist systems, and several types of manual brake setups that have the advantage of providing constant brake performance regardless of what the engine is doing. Here are a few for you to contemplate when planning your next build or revamping your current rig.

When space is tight, such as after an engine swap, it may still be possible to fit a smaller vacuum booster in the engine compartment. There are aftermarket sources that can provide a complete system, including a new pedal assembly and firewall mount.
Hydro-boost master cylinders use a boost unit at the firewall that gains its mechanical advantage from pressurized fluid provided by the power steering pump. These can be sourced from multiple OEM vehicles, including Chevy Astro vans and some fullsize trucks. One does require the added complication of plumbing the booster into the power steering system.
Aftermarket pedal assemblies and master cylinders are available to create your own manual brake setup. This particular system using Wilwood and AFCO components uses side-by-side masters, one for front and one for rear brakes. Different cylinder bore sizes can be used for front and rear if needed, and a balance bar on the pedal assembly can be adjusted to set the front-to-rear brake biasing.
When considering how much mechanical advantage can be derived from a pedal assembly, it’s simply a matter of leverage ratio, as shown here. In this case, the pedal pressure is multiplied four times at the master cylinder rod, and the rod moves one-quarter the distance that the pedal moves. Aftermarket manual pedal assemblies will state their pedal ratio for comparison.

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