Volkswagen Front Wheel Drive 1974-1989 Repair Guide

General Description

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The base model 1975-78 Rabbit is equipped with front and rear drum brakes. Some 1976-78 Rabbits, most 1979 and later Rabbits, and all Quantums, Dashers, Jettas, Foxes and Sciroccos are equipped with front disc brakes and rear drum brakes. Some models may also be equipped with front and rear disc brakes. Some late model Jettas are equipped with anti-lock brakes as an option.

The hydraulic system is a dual circuit type that has the advantage of retaining 50 percent of braking effectiveness in the event of failure in one system. The circuits are arranged so that you always have one front and one rear brake for a more controlled emergency stop (the right front and left rear are in one circuit; the left front and right rear are in the second circuit).

There is also a brake failure switch and a proportioning valve. The brake failure unit is a hydraulic valve/electrical switch which warns of brake problems by means of a warning light on the instrument panel. A piston inside the switch is kept centered by one brake system pressure on one side and the other system pressure on the opposite side. Should a failure occur in one system, the piston would go to the failed side and complete an electrical circuit to the warning lamp. This switch also functions as a parking brake reminder light and will go out when the parking brake is released. The proportioning valve (actually two separate valves on manual transaxle equipped Dasher sedans) provides balanced front-to-rear braking during hard stops. Extreme brake line pressure will overcome the spring pressure on the piston within the valve causing it to proportionately restrict pressure to the rear brakes. In this manner, the rear brakes are kept from locking. The proportioner doesn't operate under normal braking conditions.

The Anti-lock Brake System (ABS) available on some Jettas, is a three-channel system. It includes a hydraulic modulator, a pressure accumulator, speed sensors at each wheel and an electronic control unit. The control unit is equipped with a self-diagnostic program and is capable of storing fault codes. The code memory can only be accessed with the dealer's diagnostic equipment. The system operates at very high pressure and is capable of generating these pressures even when the engine is not running. Because of the need for special equipment and the dangerous pressures involved, owner service to this brake system is very limited.

 
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