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.