See Figure 1
The Teves Mark II 4 Wheel Anti-Lock Brake (ABS) system is a compact integral power brake system that uses brake fluid for both brake function and hydraulic boost. The system is used on 1987-88 Thunderbird Turbo Coupe and 1989-92 Thunderbird Super Coupe and Cougar XR-7 models.
The hydraulic pump maintains between 2,030 to 2,610 psi (13,997-17,996 kpa) pressure in the accumulator which is connected by a high pressure hose to the booster chamber and control valve. When the brakes are applied, a scissor/lever mechanism activates the control valve and pressure, proportional to brake pedal travel, enters the booster chamber. The pressure is transmitted through the normally open solenoid valve through the proportioning valve to the rear brakes. The same pressure moves the booster piston against the master cylinder piston, shutting off the central valves in the master cylinder. This applies pressure to the front wheels through the two normally open solenoid valves. The electronic controller monitors the electro-mechanical components of the system. Malfunction of the anti-lock system will cause the electronic controller to shut off or inhibit the anti-lock system. Normal power assisted braking remains if the anti-lock system shuts off. Malfunctions are indicated by one or two warning lamps inside the vehicle.
The 4-wheel anti-lock system is self-monitoring. When the ignition switch is placed in the Run position, the electronic controller will preform a preliminary self check on the anti-lock electrical system as indicated by a three to four second illumination of the amber Check Anti-Lock Brakes lamp in the overhead console. During vehicle operation, including normal and anti-lock braking operation is continually monitored. Should a problem occur, either the Check Anti-Lock Brakes or the Brake Warning Lamp(s) will be illuminated. The sequence of illumination of these warning lamps, combined with the problem symptoms, can determine the appropriate diagnostic tests to perform. However most malfunctions are stored as a coded number in the controller memory and pinpoint to the exact component needing servicing. Inspection of the system and any necessary repairs should be done before any further vehicle operation.
Individual front wheel brake circuits and a combined rear wheel brake circuit are used. Major components of the system are listed and outlined as follows.
Master Cylinder and Hydraulic Booster
See Figures 2 and 3
The master cylinder and brake booster are mounted in the conventional manner. The booster control valve is located in a parallel bore above the master cylinder centerline and is operated by a lever mechanism connected to the brake pedal pushrod.
A high pressure electric pump runs for short periods at frequent intervals to charge the hydraulic accumulator. The accumulator is a gas filled pressure chamber that is part of the pump and motor assembly. The pump, motor and accumulator are mounted on the master cylinder/booster assembly.
If the pump motor is allowed to run continuously for approximately 20 minutes, a thermal safety switch (inside the motor) will shut off the pump motor. A 2-10 minute cool down period is typical before normal Anti-lock braking can resume. During the cool down period, the brakes will operate under the full power brake lock-up mode.Valve Body Assembly
The valve body contains three pairs of solenoid valves, one pair for each front wheel and the third pair for both the rear wheels combined. The paired solenoid valves are inlet/outlet valves with the inlet valve normally open and the outlet valve normally closed. The valve body is bolted to the inboard side of the master cylinder/booster assembly.Reservoir and Fluid Level Warning Switches
A translucent plastic reservoir having two main chambers is connected to the pump assembly and master cylinder by two low pressure hoses. Integral fluid level switches are part of the reservoir cap assembly. The reservoir is mounted on the hydraulic unit with a screw and bracket and a push-in tube outlet that seats in a grommet mounted in the brake booster housing.Wheel Sensors
Four variable reluctance electronic sensor assemblies are used. Each is provided with toothed speed indicator ring. Each sensor is connected to an electric controller through a wiring harness on vehicles through 1988, and a coaxial cable on 1989-92 models. The front sensors are bolted to the front spindle mounted brackets. The front toothed sensor rings are pressed into the inside of the front disc rotor hubs.
On vehicles through 1988, the rear sensors are bolted to the rear brake axle adapters. The toothed rear sensor rings are pressed on the axle shafts, inboard of the axle shaft flange.
On 1989-92 models, the rear sensors are attached to the axle housing and the speed indicator rings are pressed onto the inner CV joints. The sensors and speed indicator rings are serviced separately.Electronic Controller
The electronic controller is a non-repairable unit consisting of two microprocessors and the necessary circuitry for operation. The controller monitors system operation during normal driving as well as during anti-lock (panic) braking. Under wheel locking conditions signals are triggered from the controller that open and close solenoid valves resulting in moderate pulsations in the brake pedal and equal anti-locking control to all four wheels. The electronic controller is located in the upper portion of the luggage compartment.