Detailed technical specifications (BMW 3 Series E21)

The hydraulic brake system is dual-circuit. The front service brakes are disc brakes, the rear ones are drum brakes. On the 323i model, the front and rear service brakes are disc brakes. The front and rear brake drive is hydraulic, from the pedal and the main brake cylinder with two coaxial portions, with a vacuum booster. The hydraulic system of the rear brakes has a pressure regulator.

Front wheel brakes

All models use ATE or Girling front wheel brakes with solid discs, "323i" crown, with fixed calipers, two-piston, with automatic adjustment of the gap between the shoe and the working surface. On the "323i" the front wheel brakes have ventilated discs.

Characteristics of the front wheel brake mechanisms

* The numerator contains data for "316", "318", in the denominator for "318i", "320" with 4- and 6-cylinder engines.

Rear wheel brakes

All models except "323i"

The rear wheel brakes are drum-type, with self-centering shoes.

Nominal drum diameter, mm: 250.

Increase in drum diameter after boring and grinding, mm: 250.5.

Maximum permissible drum diameter, mm: 251.

Maximum permissible drum ovality, mm: 0.05.



Wheel cylinder piston diameter, mm: 19.05.

Brand and type of friction linings:

• all models except "320" with 6-cylinder engine: Energit 336 or Jurid 118;
• "320" with 6-cylinder engine: Energit 336.

Brake lining width, mm: 450±0.5.

Friction lining thickness, mm: 5^-0,3.

Minimum friction lining thickness (when worn out), mm: 3.

Model "323i"

Rear wheel brakes with solid discs, with fixed calipers, single-piston, with automatic adjustment of the gap between the shoe and the working surface.

Brand and type of support: ATE F 27.

Outer disc diameter, mm: 258^-0,2.

Disc thickness, mm: 10.

Minimum disc thickness during operation, mm: 9.

Permissible difference in thickness of the working surface of the disk, mm, no more than: 0.02.

Permissible disk imbalance, gf cm, no more than: 50.

Axial runout of the working surface of the disk, mm:

• when measured on a car: 0.2;
• when measured on a removed disk: 0.05.

Wheel cylinder piston diameter, mm: 27.

Brand and type of brake pads: Textar T 260 FF.

Marking (color of labels): yellow-green-yellow.

Minimum friction lining thickness (when worn out), mm: 2.

Master brake cylinder

Main brake cylinder with two coaxial pistons, brand TH2.

Diameter of the main brake cylinder, mm: 20.64.

Piston stroke, mm:

• front brake circuit drive: 20;
• rear brake circuit drive: 14.

Vacuum booster

Brand and type: ATE T 52.

Piston diameter, mm:

• 4-cylinder cars: 200;
• cars with 6-cylinder engines: 225.

Pressure regulator

Brand and type: ATE BRMS/18.

Piston diameter, mm: 18.

Regulator switch-on pressure, kg/cm²: 25.

Marking: number "25" on the front end of the regulator.

Parking brake system

All models use a hand-operated parking brake system, which acts (except for the "323i") on the rear brake shoes. On the "323i" the parking brake is a drum brake, the wheel hub acting as the drum.

Inner drum diameter, mm: 160^+0,16.

Permissible drum ovality, mm, no more than: 0.1.

Brand and type of friction linings: Energit 338 NN.

Brake shoe width, mm 25±0.2.

When the parking system is adjusted correctly, the lever should move no more than 5 teeth of the sector.

Brake fluid

Used brake fluid: ATE, BMW, Castrol according to DOT 4. Frequency of checking the brake fluid level: not less than every 15,000 km.

Frequency of brake fluid replacement: at least once a year.

Tightening torques of main threaded connections, kgf·m

• Bolt for mounting the caliper to the steering knuckle: 8.0-9.5.
• Brake disc mounting bolt to wheel hub: 6.0-6.7 (M8: 1.5-1.8).
• Bolt for fastening the protective cover to the brake disc: 0.9-1.0.
• Brake hose tip and brake line fittings 1.3-1.6.
• Connecting bolt of the caliper halves: 2.6-3.0.
• Nut securing the master cylinder to the vacuum booster: 2.5-2.9.
• Nut for fastening the vacuum booster to the bracket: 2.2—2.4.
• Brake shield to suspension arm mounting bolt: 6.6-6.7 (apply a thread sealant such as Loctite 270 to the threads first).
• Wheel mounting bolt: 8.1-9.0.

(The article text was copied from an online resource «bmwman.ru»)