Type
Discs all round, dual hydraulic circuit supplied by main hydraulic system, automatic rear brake limitation. Front pad wear warning system. Cable operated handbrake to front wheel discs.
ABS type
Electro-hydraulic controlled anti-lock brake system, complementary to standard system.
Front brakes
| Disc diameter | 266 mm |
| Disc Thickness New | 20.4 mm |
| Maximum disc run-out | 0.2 mm |
| Minimum pad lining thickness | Indicated by warning lamp |
Rear brakes
| Disc diameter | 224 mm |
| Disc Thickness New | 7 mm |
| Wear limit | 4 mm |
| Maximum disc run-out | 0.2 mm |
| Minimum pad lining thickness | 2 mm – suggested |
Pedal
Brake pedal-to-compensator valve clearance:
| 1st type | 1.0 to 3.0 mm |
| 2nd type | 0.1 to 1.0 mm |
Wheel sensor – ABS
Air gap (non-adjustable)
| Front | 0.30 to 1.0 mm |
| Rear | 0.50 to 1.10 mm |
General Information
This dual circuit system, with disc brakes fitted to all wheels, is hydraulically operated from the main hydraulic system.
The front brakes are supplied from the hydraulic pressure regulator and the rear brakes are supplied from the rear suspension system. This arrangement favours the front brakes and imposes a braking effort limitation on the rear axle in relation to the load. The braking action is applied through the brake pedal operating a hydraulic control valve which allows pressure to the braking system.
The front brake pads are equipped with internal electric leads which operate a warning lamp on the instrument panel when the linings are due for renewal.
The front brake calipers comprise outer halves which are removable and inner halves which are integral with the steering knuckles.
The rear brake pads and calipers are mounted on the rear suspension arms The pads do not incorporate a warning system.
The handbrake is operated by a floor mounted lever. Cables run to and operate each front caliper to force the friction pads against the discs.
Anti-lock braking system (ABS)
An anti-lock braking system is fitted to the BX 16v.The function of the ABS is to prevent the brakes from locking the roadwheels when applied, thereby retaining steering control and giving the shortest-possible stopping distance for emergency braking. The system operates at speeds in excess of 5 mph and when in operation, controls the vehicle deceleration until it is brought to a halt.
The ABS monitors the rotational speed of each roadwheel during braking. If any wheel begins to slow at a faster rate than the others thereby showing that it is on the point of locking, the ABS reduces the hydraulic pressure to that wheel’s brake caliper. As the wheel grips again, its rotational speed matches the others and hydraulic pressure to the caliper is restored. This cycle can be repeated several times per second.
The ABS is operated by the following hydraulic and electronic components, which are complementary to the standard brake system.
- Front and rear wheel sensor units – on the driveshaft joints/wheel hubs.
- Hydraulic control block unit – on the left-hand wheel arch in the engine compartment.
- Electronic control unit (ECU) – under the front passenger seat.
In common with the standard system, the front and rear brake hydraulic circuits are separate but the ABS differs in also separating the right and left-hand front brake circuits. The remaining brake system components and layout are otherwise the same as standard.
The hydraulic control block contains six electro-valves, each of the three brake circuits having its own idle and return valve which work in accordance with the ECU.
The electronic part of the system comprises the ECU and a speed sensor unit for each roadwheel. Each driveshaft outer CV joint and each rear wheel hub has a toothed rotor, the speed of which is recorded by the adjacent sensor unit. This unit in turn relays the signal to the ECU. From the signals received by the ECU from each roadwheel, the average road speed is calculated and any sudden acceleration or deceleration accounted.
An automatic checking device is built into the electronic control unit. Any faults in the ABS will illuminate the yellow warning light on the instrument panel and cancel the ABS (but still allow normal braking). The yellow warning light will also light up when the ignition is initially switched on but will cancel as soon as the engine is started.
If a fault develops or is suspected in the ABS, then the system must be checked by a suitable mechanic.
Further details of the system are available in the Downloads section which features pages from the Technical Manuals.
