GB/T 18274-2017Technical specifications for motor vehicle brake system (English PDF)

4.1 Basic requirements

4.1.1 Diagnose the failure of the brake system before repair; find out and determine the cause and location of the failure; meanwhile make a record.

4.1.2 The brake shall be dismantled according to the following requirements.

4.1.3 The following operations shall be performed after the brake is dissembled.

4.2.1 Brake caliper

4.2.1.1 The brake caliper cylinder shall be free of rust or damage; otherwise it shall be replaced.

4.2.2 Brake disc

4.2.2.1 The brake disc shall be free of cracks; its working surface shall be free of rust spots or shrinkage holes or the like defects.

4.2.2.2 The total thickness of vehicle bake disc shall meet the original technical requirements of the manufacturer; if there is no specified value, it shall be no less than the standard thickness of 2.0mm; the maximum amount of radical runout shall be 0.15mm; the depth of scratch groove shall be no greater than 0.38mm.

4.2.3 Brake friction block

4.2.3.1 There shall be free of cracks or burns; the wear shall be uniform.

4.2.3.2 After wearing, the thickness of the brake friction block of vehicle shall meet the original technical requirements of the manufacturer; if there is no specified thickness value, and the value is less than 1.5mm, then it shall be replaced.

4.2.4 Maintenance data

4.2.4.1 The maintenance reference data of the common brake disc and brake friction block of the vehicles can see Table A.1.

4.2.4.2 The maintenance reference data of the common brake disc and brake friction block of the large passenger car can see Table A.2.

4.3.1 Brake drum

4.3.1.1 The brake drum shall be replaced timely in the following cases.

4.3.1.2 When the brake drum is being machined, the left and right brake drums on the same axis shall be cut to the same size by the same method to ensure the use of the brake drum have the same braking performance on the both wheels. Multiple shallow cutting methods shall be used for cutting. The main axis speed is 150r/min when cutting; when taking the rough cutting, the transverse feed per revolution is 0.15mm~0.20mm; when taking the fine cutting, the transverse feed per revolution is no greater than 0.05mm.

4.3.2 Brake shoes and brake base plate

4.3.2.1 After the brake drum is disassembled, inspect each brake shoes, brake shoe return springs, compression spring and support pins, and the like components.

4.3.2.7 Clean the brake shoe and remove the burr; the mating clearance between the brake shoe pin hole and support pin shall meet the original technical requirements of the manufacturer; if there is no specified clearance value, it shall be no greater than 0.30mm.

4.3.2.8 If the brake base plate has distortion, cracks, or grooves, it shall be replaced. Tighten the fixing bolts of the brake base plate and the support pin fixed by the bolts as per the specified torque. The brake baes plate has no rust or other surface defects.

4.3.2.9 When the free length and elasticity of the brake shoe return sprint and compression spring change, exceeds the original technical requirements of the manufacturer, or when there is twisting, bending, or hook damaging, it shall be replaced.

4.3.3 Brake clearance After the brake is installed, adjust the brake clearance; the wheel shall be rotate freely without any drag. The clearance between the brake shoe lining and brake drum shall meet the original technical requirements of the manufacturer; if there is no specification, the clearance shall be 0.20mm~0.40mm.

4.4.1 Air compressor

4.4.5 Oil-water separator The pressure on inlet and outlet of the oil-water separator shall be equal. The air pressure of the safety valve shall be adjusted according to the original technical requirements of the manufacturer; and work soundly. The filter core shall be cleaned and worked reliably; all valves and gaskets shall not have cracks or aging phenomena.

4.4.8 Brake pedal The clearance between the brake pedal bushing and the pedal shaft shall be no greater than 0.3mm. Under the normal assembly and use conditions, the brake pedal assembly shall ensure the flexible and light brake operation. The free stroke of the brake pedal shall meet the original technical requirements of the manufacturer.

4.5.1 Brake master cylinder and wheel cylinder

4.5.1.1 The mating clearance between the master cylinder piston and cylinder of hydraulic brake shall meet the original technical requirements of manufacturer.

4.5.1.2 The surface roughness of the cylinder of the master cylinder and wheel cylinder in the stroke of the piston and on the outer cylindrical surface of the piston shall be no greater than Ra 0.8.

4.5.1.3 The tolerance BETWEEN cylinder of master cylinder and wheel cylinder AND outer diameter of piston shall meet the original technical requirements of the manufacturer; The dimensional tolerance of the inner hole of the cylinder of the wheel cylinder shall be selected as per Table 2.

4.6 Parking brake device

4.6.1 Each control device and transmission device of the parking brake system shall have good performance and reliable operation.

4.6.2 Check and adjust the parking brake clearance and free stroke, so that they meet the original technical requirements of the manufacturer.

4.6.3 Check the parking brake indicator switch, when the parking brake level is pulled up, it shall be ignited; when it is released, it shall be extinguished.

4.6.4 Check the parking brake performance, under the no-load conditions, the parking brake device shall be able to ensure the vehicle to maintain motionless in the positive and negative directions on the 20% slope (15% for the vehicles with total mass about

1.2 times less of the unladen mass), or on the slope with the adhesion coefficient between tyre and road greater than or equal to 0.7; the time shall be greater than or equal to 5min; the locking device is reliable.