The safety of passengers and drivers on the route depends on the serviceability of the brakes, especially in conditions of intensive urban traffic. Brake system of the PAZ bus It is a complex pneumatic complex that requires constant monitoring and timely maintenance. Modern models such as PAZ-3205, PAZ-4234 tourist PAZ-3204They are equipped with efficient but demanding air quality units.
Owners and mechanics need to clearly understand the principle of operation of the pneumatic drive in order to quickly detect leaks or malfunctions in the operation of regulators. The critical parameter is the filling time of the air receivers to the operating pressure, which should not exceed the manufacturer's standards. Ignoring the slightest signs of malfunction can lead to an emergency on the road, so diagnosis should be regular.
In this article, we will analyze in detail the pneumatic device, consider typical problems and ways to eliminate them, and also pay attention to the features of the anti-lock system. You will learn how to properly adjust the gaps and what to pay attention to when planning maintenance.
General scheme and principle of operation of pneumatics
The basis of the entire system is a compressor that pumps air into the receivers, creating a reserve of energy for the operation of all mechanisms. On PAZ buses, two-cylinder compressors are most often installed, providing sufficient performance even with frequent braking. The air passes through the moisture separator, where it is cleared of oil and condensate before it reaches the main highways.
Then the compressed air is distributed along the circuits through a four-circuit protective valve. This element ensures that when one of the circuits is depressurized, the rest will continue to function, providing the possibility of stopping the vehicle. The pressure in the system is controlled by sensors and pressure gauges located on the driver's dashboard.
It is important to understand that pneumatic actuator It does not work instantly, as a hydraulic, but with a small delay due to the speed of the air wave through the tubes. That is why the serviceability of all valves and tightness of connections play a crucial role. Any microcrack in the tube can cause the pressure to drop below the critical mark.
- 🔹 The compressor creates a supply of compressed air for the entire system.
- 🔹 The moisture separator removes oil impurities and water, protecting the valves from corrosion.
- 🔹 Safety valves divide the system into independent circuits for safety.
- 🔹 Receivers store energy for repeated braking without the participation of the engine.
⚠️ Attention: If after starting the engine the pressure in the circuits does not grow or grows very slowly, immediately shut off the engine and check the tension of the compressor drive belt. Operation of a bus with a non-functioning compressor is prohibited.
Device of working and parking circuits
The working brake system on PAZ buses is usually double-circuit, which corresponds to modern safety standards. When pressing the brake pedal, compressed air from the receivers enters the brake chambers of the wheel mechanisms. There, the energy of the compressed air is converted into mechanical motion, diluting the pads and pressing them against the drums.
The parking brake (handle) acts on the wheels of the rear axle and is activated by spring-loaded energy accumulators. To release the brakes, it is necessary to supply air to the chambers, which compresses powerful springs. This means that when the system is completely pressure-free, the bus will automatically brake, which is an important element of passive safety.
Adjustment of the gaps between the pads and drums is carried out automatically or manually using adjusting screws, depending on the model of the brake chambers. On modern modifications PAZ-32053 Automatically adjusted cameras are often found, but mechanics should periodically check their performance visually.
Particular attention should be paid to the state of brake-chamber. Their membranes should not have cracks, and the rods should walk freely, without distortions. The rod jamming can lead to overheating of the wheel and even a tyre fire.
- 🔸 The working circuit is activated by the pedal and provides a stop in motion.
- 🔸 The parking circuit holds the bus in place and runs on spring batteries.
- 🔸 Automatic adjustment of gaps requires periodic check of the course of the rod.
⚠️ Attention: Never attempt to shut down or disassemble the spring-loaded parking brake batteries without using a special spring compression tool. This can lead to severe injuries due to the sudden release of energy.
Anti-lock system (ABS/ABS) on PAZ
Modern PAZ buses are equipped with an electronic system to prevent wheel locking during braking. ABS analyzes the speed of rotation of each wheel using sensors and, when blocked, briefly relieves pressure in the corresponding circuit. This allows you to maintain the course stability and controllability of the bus.
The main elements of the system are the control unit (ECU), pressure modulator and sensors of the speed of rotation of wheels. If any of these components fails, the ABS control lamp lights up on the dashboard, and the system goes into emergency mode, working like a normal braking system without anti-locking.
Diagnostics of ABS requires a special scanner that reads error codes from the memory of the ECU. However, the initial check can be carried out visually, examining the integrity of the sensor wiring and the reliability of their attachment. Often problems arise due to oxidation of contacts or damage to wires at bending sites.
Typical ABS error codes for PAZ
4.1.1 - Break of the front left wheel sensor circuit. 4.2.3 Short circuit of the modulator valve. 6.5.0 - Failure of the pump relay. The exact decoding depends on the system manufacturer (WABCO, Knorr-Bremse or domestic analogues).
This is a normal workflow, not a sign of a breakdown.
- 🔹 The speed sensors transmit a signal to the ECU about the rotation of the wheels.
- 🔹 The modulator regulates the air pressure in the brake chambers.
- 🔹 The control lamp signals the transition to emergency mode.
Adjustment of brake mechanisms and replacement of pads
The process of replacing brake pads on PAZ buses requires compliance with a certain sequence of actions. First, you need to raise the bridge to the jacks or viewing ditch, remove the wheels and clean the mechanisms of dirt. The brake drum is then removed, which may require the pads to be removed through the adjustment holes.
After installing new shoes, the gaps are necessarily adjusted. The stroke of the brake chamber rod at full pedal stroke shall not exceed 40 mm for standard type 24 and 50 mm for extended stroke chambers. Exceeding these values indicates the need for adjustment or replacement of linings.
When assembling the unit, it is necessary to lubricate the opening fist and bushings with a special high-temperature lubricant resistant to washing. The use of inappropriate lubricants can lead to souring of the mechanism and brake failure.
☑️ Checklist for shoe replacement
Don’t forget to check the condition of the brake drums. The presence of deep risks, cracks or the development of a more permissible norm requires mandatory flow or replacement of the part. Ignoring this rule will lead to rapid wear of new pads and reduce the effectiveness of braking.
Table of typical faults and methods of elimination
For a quick diagnosis of problems, below is a table with the most common symptoms and probable causes. Use it as a reference material for repairs.
| Malfunction | Probable cause | Elimination method |
|---|---|---|
| Pressure drop when pressed on the pedal | Leaky pipes or chambers | Search for leakage with soap solution, replacement of seals |
| The bus takes you away when braking. | Different gaps of pads or oiling of linings | Adjusting gaps, replacing pads, checking the ossels |
| Screaming or screeching when braking | Wearing of the pads, hitting sand | Replacement of pads, cleaning of mechanisms |
| The compressor is not switched off (pumping) | Failure of the pressure regulator or valve | Replacement of pressure regulator, valve inspection |
| The brake malfunction lamp lit up. | A drop in pressure in one of the circuits | Checking the tightness of the contours, checking the sensors |
When looking for leaks in pneumatic Use the soap solution effectively. Apply it to suspicious joints and connections - the appearance of bubbles will indicate the place of air exit. Pay special attention to the connections of tubes with plastic fittings, which over time can lose elasticity.
When replacing brake pads, always change them on all wheels of one axle. Installing new pads on one side and old ones on the other will result in uneven braking and the bus pulling away.
Features of service in the winter
Winter operation of PAZ buses imposes increased requirements for the condition of the pneumatic system. The main problem is the freezing of condensate in the highways and valves, which can completely paralyze the brakes. To prevent this, it is necessary to drain condensate from receivers regularly (every week or more often during intensive operation).
The use of high-quality antifreeze in the pneumosystem (alcohol-containing liquid) is allowed only in emergency cases and in strictly recommended proportions by the manufacturer. The constant addition of alcohol can cause the rubber seals and membranes to swell, causing them to break down.
In the cold season, it is recommended to check the work of the air dehumidifier more often. If it stops effectively purifying the air, moisture will quickly fill the system. In severe frosts, valve failure due to freezing is possible, so the bus is better stored in a warm garage or in a heated parking lot.
⚠️ Attention: It is strictly forbidden to start a fire under receivers or valves to heat a frozen system. This can cause the receivers to explode due to a sharp increase in pressure and temperature, as well as to melt plastic elements.
Timely replacement of the air filter compressor is also critical in winter. Clogged filter makes the compressor work with overload, and in winter it can clog with ice crumb, completely blocking air access.
Regular drain of condensate and a serviceable moisture separator is the key to the trouble-free operation of PAZ brakes in winter. Ignoring this procedure leads to costly repairs of the entire pneumatics.
Frequently Asked Questions (FAQ)
What is the normal pressure in the brake system of the bus PAZ?
The normal operating pressure in the system is considered to be a range from 6.5 to 8.0 atmospheres (bar). The compressor should be turned off (go into idling mode) when reaching 8.0 atm, and be turned on again when falling to 6.5 atm. Driving below 5.5 atm is prohibited.
How often should I change the brake pads on the PAZ-3205?
The resource of the shoe depends on the operating conditions (urban cycle or highway) and driving style. On average, replacements are made every 40-60,000 kilometers of mileage. However, the main criterion is the thickness of the friction lining: if it is less than 4 mm, the pads are subject to mandatory replacement.
Why is the air poisoning from under the brake pedal?
Air leakage in the area of the brake pedal most often indicates a malfunction of the main brake crane. Perhaps the rubber seals or valve inside the crane were worn. Replacement or repair of the main brake crane is required.
Can I drive if the ABS lamp is on?
You can drive, but with caution. A lighted ABS lamp means that the anti-lock system is disabled and braking occurs in normal mode. However, on a slippery road, the wheels may be blocked, which will lead to skids. Repairs are desirable to be carried out soon.