Brake balance bar set-up

Purpose: The function of a balance bar is to allow the adjustment of brake line pressure distribution between two master cylinders. This is accomplished through moving the balance bar pivot towards one master cylinder pushrod or the other. If the pivot is perfectly centered between the pushrods, the force applied to each master cylinder will be equal. This is called the “neutral position” of the bias adjuster. If the pivot is moved closer to one pushrod or the other, then the master cylinders will receive differential pressures that are proportional to the distance between the balance bar pivot point and master cylinder center lines. Being able to move the pivot point allows the driver to make incremental adjustments to the braking characteristics of the car (front-to-rear brake bias) and to alter those characteristics to account for changes in fuel load, track conditions and handling of the car.

Setting up the brake balance bar: The brake balance bar is one of the most overlooked and least understood components on a racecar. As with all aspects of racecar assembly and preparation, careful attention to the geometry of the brake balance bar and brake pedal will yield great benefits.

To start with, look for proper installation of the brake balance bar bias adjuster and ensure that the brake balance bar pivot bearing is free to move within the pedal tube or trunnion housing. The pedal tube or trunnion housing can become distorted during installation if this is the case, then the tube can be reworked with a master cylinder hone until the bearing slides smoothly from one end of the tube to the other. The tube must be clean and sparingly lubricated with light oil or dry Teflon spray.

Next, find the distance between the centerlines of the front and rear master cylinders. Typically, this could be 2½ inches but is not critical. What’s critical is that this measurement, whatever it is, is exactly duplicated in the center-to-center distance of the clevises threaded onto the bias adjuster. This ensures that the master cylinder pushrods are actuated properly, minimizing any side loads applied to the master cylinder piston and bore.

With the clevises set on the bias adjuster, measure the distance between them and the balance tube itself. If the clearance between each clevis and the balance tube is more than 0.060” (1.5mm) then shims must be added until the proper airgap is achieved. This will prevent the balance bar from shifting while on the track and causing unpredictable change in the brake bias of the car.

With the balance bar connected to the master cylinders, and brake lines connected, the brakes should be bled. It is critical that front and rear brake circuits be bled simultaneously so that both master cylinders are allowed to use their full travel and prevent binding or distortion of the bias adjuster.

Once satisfied that the clevises and pedal tube clearances have been properly set, now look at master cylinder pushrod length. The key is to set the bias adjuster so that it is perpendicular to the master cylinder centerlines when the brake pedal is under pressure. Typically, this means that the front master cylinder pushrod will be 0.120”–0.200” (3mm-5mm) longer than the rear master cylinder pushrod when at rest. This is due to the front braking circuit having a larger fluid volume needed to feed the larger piston diameters of the front calipers. As a result, the front master cylinder requires a higher feed rate than does the rear. If the pushrod lengths are equal, then the feed rate of the rear master cylinder is too high relative to the front and that would result in the rear circuit “hitting” before the front. So, with the pushrod lengths adjusted properly, the balance bar will be square under compression with the front and rear circuits “hitting” approximately at the same moment.

Brake pedal geometry: With the balance bar geometry correctly positioned, now look at the brake pedal geometry. For the brake system to work properly, it is important that the brake pedal gets hard before it crosses the vertical plane of the brake pedal pivot. If the brake pedal crosses the vertical plane of the pedal pivot (goes “over center”) then the mechanical advantage of the pedal, over the pushrods, will be lost. That would result in a loss of pedal feel and braking force. Adjust the pedal “over center” position with a separate pedal height adjuster, if available, or by lengthening both master cylinder pushrods by the same amount and until the desired pedal height is achieved. As a result, the throttle pedal may need to be adjusted to restore the proper heel-and-toe pedal relationship. If there is insufficient adjustment available, then this can be accomplished by attaching a simple spacer to the throttle pedal.