GM Astro/Safari 1985-1996 Repair Guide

HYDRAULIC BRAKE SYSTEM

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See Figures 1 and 2

These vans are equipped with independent front and rear brake systems. The systems consist of a power booster, a master cylinder, a combination valve, front disc and rear drum assemblies.

The 1989 models are equipped with Rear Wheel Anti-Lock (RWAL) brakes. The system is designed to reduce the occurrence of rear wheel lockup during a severe brake application. A pressure regulator limits the amount of hydraulic line pressure to the rear brakes by the use of a control valve. The valve is controlled by a microcomputer which is tied in with the Electronic Control Unit (ECU). The ECU is mounted next to the master cylinder.

The 1990 and on models could be ordered with 4-Wheel Anti-Lock (4WAL) brakes as an option. The system is designed to reduce the occurrence of wheel lockup during a severe brake application. The system regulates hydraulic line pressure by the use of an Electro-Hydraulic Control Unit (EHCU) valve located under the master cylinder. An isolation valve maintains pressure to each wheel separately and the rear wheels combined.



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Fig. Fig. 1: Rear wheel anti-lock brake system



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Fig. Fig. 2: Four wheel anti-lock brake system

 
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