Single-anchor, internal-expanding, duo-servo, self-adjusting, hydraulic drum brakes with a safety, dual master cylinder are used on the front of Ford vans through 1974 and on the rear of all years.
Disc front brakes are used on 1975 and later models; dual piston on E-250 and 350, single piston on E-100 and 150.
The E-100 and E-150 use a sliding caliper, single piston brake; the 1975 E-250 and E-350 and some 1979-88 use a floating caliper, dual piston brake; and the 1976 and later E-250 and E-350 and some 1979-88 E-100, 150 use a rail sliding caliper, dual piston brake. Both he floating and sliding calipers are allowed to move slightly to align with the disc (rotor). The floating caliper is retained by through-bolts, and the sliding caliper by a key.
The dual, safety-type master cylinder contains a double hydraulic with two fluid reservoirs, two hydraulic pistons (a primary and a secondary), and two residual check valves on all-drum systems, located in the outlet ports. The master cylinder's primary and secondary pistons function simultaneously when both the primary and secondary systems are fully operative.
Failure in either the front or rear brake system does not result in failure of the entire hydraulic brake system. Should hydraulic failure occur in the rear system, the hydraulic pressure from the primary piston (which actuates the front brakes) causes the secondary piston to bottom out in its bore, due to the lack of hydraulic pressure. The primary piston then actuates the front brakes with the continued stroke of the brake pedal.
Clean, high-quality brake fluid is essential to the safe and proper operation of the brake system. You should always buy the highest quality brake fluid that is available. If the brake fluid becomes contaminated, drain and flush the system and fill the master cylinder with new fluid.
The system has a pressure differential valve that activates a warning light if either hydraulic circuit is losing pressure. On 1975 and later models, the pressure differential valve id combined with a metering valve that restricts flow to the front brakes until the rear brakes overcome their retracting spring to prevent front brake lockup, and a proportioning valve that limits rear brake hydraulic pressure to prevent rear brake lockup.