Vehicles are equipped with working, parking, spare and auxiliary brake systems, as well as devices for connecting the brake system of a semi-trailer with a two-wire pneumatic drive and outputs for supplying other consumers with compressed air
A working brake system acts on the brake mechanisms of all wheels of the car.
The drive mechanisms are pneumatic with separate braking of the front and rear wheels.
In the drive of the brake mechanisms, electro-pneumatic pressure modulators of the anti-lock braking system (ABS) of the brakes can be installed.
Parking and spare brake systems act on the brakes of the middle and rear axles,
which are actuated by means of brake chambers with spring energy accumulators (Fig. 1, 2). Control is carried out using a crane in the driver's cab.
The parking brake also functions as a spare.
It is designed to brake the car in the event of a complete or partial failure of the service brake system.
When the parking brake system is applied, the control valve handle is set (by turning) to the extreme fixed position.
The compressed air that compresses the power springs of the energy accumulators is released into the atmosphere, and the spring actuates the brake mechanisms.
When the emergency brake system is engaged, the parking brake control valve handle is held in any intermediate non-fixed position.
With an increase in the angle of rotation of the handle, the intensity of braking increases due to a decrease in air pressure, which compresses the springs of the energy accumulators.
The parking brake system of MAZ-631705, 631708, 642505, 642508, 533605 cars can be made in two versions:
1) The parking brake system acts on the brake mechanisms of the middle and rear axles, which are actuated by means of brake chambers with spring energy accumulators.
Control is carried out using a crane in the driver's cab.
The same system functions as a spare. It is designed to brake the car in the event of a complete or partial failure of the service brake system.
When the emergency brake system is turned on, the parking brake control valve handle is held by the driver in any intermediate non-fixed position.
The intensity of braking increases with the increase in the angle of rotation of the handle.
2) The parking system consists of two independent systems: the main one, acting through the transmission on the wheels of the middle and rear axles of the car, and the additional one, acting on the wheels of the rear axle and controlling the brakes of the trailer.
The main parking brake system includes a drum brake (Fig. 3) mounted on the output shaft of the transfer case in the drive of the middle and rear axles, and a mechanical, multi-way manual brake actuator (Fig. 4).
The auxiliary parking brake system includes the service brakes of the rear axle of the vehicle, the circuit for driving the brakes of the trailer and the brakes of the rear axle of the vehicle, and a manually operated valve.
The crane has a follow-up action on the angle of rotation of the handle, which allows you to adjust the intensity of braking when using this brake system as a spare.
An additional parking brake system is used for short-term braking of a road train together with the main brake system on roads with a slope of more than 12%.
The auxiliary brake system acts on the vehicle's transmission by creating back pressure in the exhaust system using an air-actuated throttle.
It is designed to slow down the car on long descents of mountain roads. When the throttle is turned, the fuel supply is turned off at the same time.
When the tractor vehicle is braked by the working or parking (spare) systems, the semi-trailer is simultaneously braked.
Possible brake problems
Pneumatic system air tanks do not fill or fill slowly (pressure regulator does not work):
- The pneumatic system has a significant compressed air leak. Shl damaged hangers and pipelines. insufficient tightening of joints, pipelines, hoses, connections and adapter fittings - Replace hoses and pipelines. Tighten the connections. Replace defective parts of joints and seals
- Insufficient tightening of body parts of the devices. The body parts of the devices are leaking due to poor quality casting - Tighten the fastening of the body parts. Replace machine
- The machine has failed. Leak occurs through atmospheric outlet of apparatus - Replace apparatus
- Air bottle leaking - Replace bottle
- The drying cartridge of the air dryer is frozen or clogged - Check the air outlet from port 21. In case of malfunction, warm the cartridge with hot water
- Permanent air exhaust through the outlet port of the compressed air dryer (in winter) - See description of the dryer
The air cylinders of the pneumatic system are not filled (the pressure regulator is activated):
- Pressure regulator set incorrectly - Adjust pressure regulator with adjusting screw, replace pressure regulator if necessary
- Presence of kinks and collapse of pipelines - Replace the pipeline
- Presence of a transport plug or foreign bodies in the pipeline - Remove the plug and foreign objects, blow out the pipeline with compressed air
- Incorrectly adjusted 4-way safety valve - Check and adjust or replace if necessary
The pressure in the cylinders of the circuits is high or low with the pressure regulator operating:
- Faulty pressure gauge - Replace
- Pressure regulator out of adjustment - Adjust regulator with adjusting screw. If it is not adjustable, replace the regulator
- 4-way valve misadjusted - Adjust or replace
Inefficient braking or no braking of the vehicle by the service brake when the brake pedal is fully depressed:
- Brake valve defective - Replace brake valve
- Contamination of the cavity under the rubber boot of the two-section brake valve drive lever - Clean the cavity under the rubber boot from dirt. Replace case if necessary
- The presence of a significant leakage of compressed air in the lines of I and II circuits after the brake valve - Replace hoses and pipelines. Tighten the joints.
- The drive of the brake valve is not adjusted - Adjust the drive
- Incorrect setting of the brake force regulator actuator - Adjust the setting of the brake force regulator or replace the brake force regulator
- The stroke of the brake chambers exceeds the set value - Adjust the stroke of the pistons, Replace the adjusting lever (with automatic adjustment)
- Brake pad wear - Check brake pad thickness and replace if necessary
When the parking brake valve handle is set to the released position, air leaks from the brake valve or relay valve:
- Rupture of the diaphragm of the rings in the trailer brake control valve - Air must not enter port 42 of the trailer valve. Replace worn parts and trailer brake control valve
- The seal between the energy storage cavity and the working chamber is broken - Identify the damaged chamber and replace it
Inefficient braking or lack of braking of the car with parking or emergency brakes:
- Defective relay valve, parking brake valve - Replace the brake device
- Clogged piping or hoses on manual valve power circuit - Clean piping and blow out with compressed air. If necessary, replace with serviceable
- Spring accumulators defective - Replace spring accumulator brake chambers
- Brake chamber strokes exceed set value - Adjust stroke
When the parking brake valve handle is set to the braked position, the car does not release the brakes:
- Leakage of air from the pipelines of the supply circuit of the valve with manual control from the atmospheric outlet of the relay valve - Eliminate the place of leakage in the ways indicated in paragraph 1
- Spring accumulator thrust bearing failed - Replace spring accumulator brake chamber
- Faulty parking brake valve - Determine if air is entering port 4 of the parking relay valve. Replace faucet
- Defective relay valve - Replace valve
- Spring accumulator air leak - Replace spring accumulator brake chamber
When the vehicle is moving, the rear bogie is braked without actuating the brake pedal and the parking brake valve:
- The brake valve is defective. Brake valve actuator set incorrectly - See brake valve actuator adjustment
- The seal between the cavity of the spring energy accumulator and the working chamber is broken - Replace the brake chamber with spring energy accumulator
- Insufficient pressure in the parking brake circuit - Check the pressure in the circuit. Check 4-circuit valve
Inefficient braking of the trailer (semi-trailer) or no braking with the brake pedal depressed or the emergency brake applied:
- Compressed air leak - Fix as described in point 1
- Faulty two-wire trailer brake control valve drive devices, coupling heads - Replace faulty parts
- Faulty trailer brakes or trailer brakes - Check the presence and level of pressure in the connecting heads of the tractor. Check the condition of the trailer brakes
There is no braking of the road train when the auxiliary brake is applied:
- The pneumatic valve for switching on the auxiliary brake is faulty. - Replace faucet
- Auxiliary brake damper actuator air cylinder defective. Faulty cylinder for shutting off the fuel supply of the damper mechanism. Leakage of compressed air
- Clogged pipes - Replace faulty cylinders. If necessary, remove the auxiliary brake components, clean from carbon deposits, wash and dry
- Fix the leak using the methods indicated in point 1. Remove the pipelines and blow with compressed air
- Brake lights do not come on when you press the brake pedal or apply the parking brake
- Faulty brake light sensor or pneumatic drive devices - Replace sensor or devices
Presence of a significant amount of oil in the pneumatic system:
- Cylinder piston ring wear - Replace compressor