broncohio

Early Bronco Brake Imbalance Switch Adjust
(or, getting the brake light to go out!)

Brake imbalance switch diagram
(click to get a bigger picture)

Early Bronco's without disk brakes did not have a proportioning valve, they
had a brake imbalance switch. If the pressure was not equal in the front and
rear brake systems, the plunger would go off center and trigger the light on
the dashboard. This is to let you know if there is a failure in your brake system.

To get the light to go out, you must recenter the plunger. The easiest way is
to bleed either the front or the rear brakes. Start by bleeding one of the
front wheel cylinders. While you are bleeding it, have someone in the truck
watch the brake light and let you know when it goes out. If it never goes
out, or it goes out then back on (you passed it), you need to repeat the
procedure, bleeding one of the rear cylinders. The light will go out once
the plunger in the switch is centered.

The Official version:

Centralizing the Pressure
Differential Valve

After any repair or bleeding of the primary (front brake) or secondary (rear brake) system, the dual-brake system warning light will usually remain illuminated due to the pressure differential valve remaining in the off-center position.
To centralize the pressure differential valve and turn off the warning light after the systems have been bled, follow the procedure below.
1. Turn ignition switch to the ACC or ON position.
2. Check the fluid level in the master cylinder reservoirs and fill them to within 1/4 in. of the top with brake fluid, if necessary.
3. Depress the brake pedal and the piston should center itself causing the brake warning light to go out.
4. Turn the ignition switch to the OFF position.
5. Before driving the vehicle, check the operation of the braked and be sure that a firm pedal is obtained.