Maintenance of brake mechanisms and brake pneumatic drive Kamaz
Maintenance of the brake mechanisms consists in lubricating the adjusting levers and bushings of the expander shafts;
- - in regulating the strokes of the brake chamber rods and fixing the brake chambers and their brackets;
- - in checking the condition of brake drums, shoes, linings, coupling springs and expanding fists (with the hubs removed).
The adjusting levers of the brake mechanisms are lubricated through the grease fittings until fresh grease is squeezed out.
The bushings of the expander shafts are also lubricated through grease fittings, but it should be borne in mind that the amount of lubricant should be moderate (no more than five strokes when lubricating with a manual syringe), as excess lubricant may enter the brake mechanism.
The stroke of the brake chamber rods is adjusted with cold brake drums and nominal air pressure in the brake pneumatic drive.
The parking brake must be off. The work is carried out by two performers, one of which must be in the cab of the car.
Measure the stroke of the rods with a ruler, setting it parallel to the rod and resting it with the end into the body of the brake chamber. They mark the location of the extreme point of the rod on the scale of the ruler, press the brake pedal all the way and again note the location of the same point of the rod on the scale.
The difference between the results obtained gives the stroke value.
If the stroke of the rod exceeds 40 mm, it is necessary to loosen the locking bolt and, by rotating the axis of the worm of the adjusting lever, spread the pads until they come into contact with the brake drum, i.e., it is necessary to rotate the axis of the worm until it stops.
After that, the pads should be brought together by turning the worm axis half a turn in the opposite direction (2 ... 43105, -5320, -5410 and -55102: for KamAZ-5511, -53212 and -54112 vehicles, it is 25 mm on the intermediate and rear axles and 20 mm on the front.
It is necessary to make sure that when turning the compressed air supply on and off, the rods of the brake chambers move quickly, without jamming.
Check the rotation of the reels. They should rotate freely without jamming, without touching the pads.
It is necessary that the rods of the right and left chambers on each axle have as much equal stroke as possible (permissible difference is not more than 2...3 mm) to obtain the same braking efficiency of the right and left wheels.
After checking that the adjustment is correct, tighten the locking bolt of the adjusting lever.
Inspection of the brake mechanisms reveals the need to replace some parts. At the same time, it is taken into account that the wear of the working surface of the brake drum is allowed no more than 1 mm, chips, cracks, chipping of brake friction linings are unacceptable, their wear must correspond to the value at which at least 0.5 mm remains to the rivet heads.
If it is necessary to replace one of the left or right / brake linings, change all linings for both brake mechanisms (left and right wheels).
After replacing the brake linings, the brake mechanism is fully adjusted.
To do this, loosen the nuts for fastening the axles of the pads and bring the eccentrics together by turning the axles of the pads so that they are located towards each other with the beveled sides of their outer ends, then by turning the axis of the worm of the adjusting lever, they press the brake pads against the drum, after that, turning the eccentric axles in one or the other side, install the pads, ensuring a snug fit to the drum.
The fit of the pads is checked with a probe 0.1 mm thick, which should not pass anywhere along the entire width of the lining. With this position of the shoes, the axle nuts are tightened and the minimum stroke of the brake chamber rod is set.
After the specified adjustment, the following gaps are achieved between the brake drum and the shoes: at the expanding fist - 0.4 mm, at the axes of the shoes - 0.2 mm.
The stroke of the brake pedal must be at least 100...130 mm, of which 20...30 mm is free play.
When fully depressed, the pedal should not reach the cab floor by 10...30 mm. The pedal travel is measured with a ruler at a distance of 210...220 mm from the axis of rotation.
The end of free play is taken as the moment when the rods of the brake chambers start to extend or the moment when the brake lights come on. If necessary, adjust the pedal stroke by changing the length of the rod 6 (see Fig. 1) with an adjusting fork 5.
With the full pedal travel of the brake valve lever, it should be 31.1 ... 39.1 mm.
Daily maintenance of the brake actuator involves a small number of operations to ensure trouble-free operation.
Basically, these are control and diagnostic works that do not require the use of instruments; they are performed by the driver when preparing the car for departure and in the process of working on the line;
To check the serviceability of the control dumps on the instrument panel, press the test button, while all control lamps should light up, they turn on even when the pressure in the receivers is less than 480 ... 520 kPa.
To check the operation of the drive, actuate the vehicle's brake controls: press the brake pedal, turn on and off the parking brake, press the auxiliary brake valve button, release the power accumulators with the emergency brake release button.
Daily, at the end of the working day, condensate is drained from the receivers.
At an air temperature of - (- 5 ° C) and below, pour (once a week or after a run of 1000 km) a fresh portion of ethyl alcohol into the anti-freeze fuse. Before pouring alcohol, it is necessary to drain the condensate from the fuse.
When connecting the trailer, check the correct connection of the connecting heads and the opening of the disconnecting taps.
When servicing the pneumatic drive of the car's brakes, you must also make sure that it is tight. Particular attention should be paid to the tightness of the connections of pipelines and flexible hoses, since air leaks most often occur here.
The places of strong air leakage are determined by ear, and weak ones - with the help of a soap emulsion.
Air leaks from the connections of the pipelines of the brake system are eliminated by tightening them and leaking pipelines and flexible hoses are replaced.
The pins of the brake chamber rods and the drive pins of the two-section crane are checked. The protective covers of the brake chambers and the brake valve must not be damaged.
During the second maintenance, the operability of the pneumatic brake drive is checked using control output valves using pressure gauges.
Check the tightening of the nuts securing the compressor to the engine and the tightening of the nuts securing the compressor cylinder head.
Tightening is done evenly in a cross pattern in two steps. They check the fastening of the clamps of the brake chambers, the fastening of the brackets of the brake chambers and the chambers themselves to the brackets.
Special attention should be paid to the fastening of energy accumulators. The backlash of their fastening is unacceptable, as this leads to the separation of the device from the bracket.
For seasonal maintenance, the compressor head must be removed to clean the pistons, valves, and seats. Compressor valves that fail to seal must be lapped or replaced.
In the pressure regulator, it is necessary to wash or replace the filter element, which is located under the bottom cover.
You need to be careful when screwing the cover, as the thread is tapered and distortions during its installation are unacceptable. They lead to thread breakage, which is then impossible to restore.
Before installation, it is recommended to lubricate the thread with graphite grease to prevent it from “seizing”.
As the compressor works, the cylinder-piston group wears out, the tightness of the valves is broken.
In case of these malfunctions, the filling time of the pneumatic system (until the control lamps go out) at a crankshaft speed of 2200 rpm exceeds the set value of 8 minutes or the compressor does not develop the set pressure at all (700 ... 750 kPa).
In addition, the wear of the cylinder-piston group leads to the suction of oil into the pneumatic system.
After filling the pneumatic system with air in the pressure regulator, the unloading valve opens and the oil that has entered the pneumatic system along with the air is thrown out and settles on the regulator and frame. This is an external sign of a compressor malfunction.
It should be noted that oil flow through the compressor may increase due to clogged air cleaner.
As the clogging increases, the vacuum at the inlet increases and the compressor, even with a working piston group, sucks in oil mist from the crankcase, and then ejects it into the pneumatic drive at the outlet.
Leakage of the compressor cylinder head gasket, internal cracks in the head or block lead to the fact that the liquid from the cooling system is sucked into the cylinders, and then, together with the air, goes to the pneumatic drive.
The coolant level in the expansion tank drops, and the liquid in it boils. This is because the piston on the compression stroke pushes air into the compressor cooling jacket, and then the air with liquid is discharged into the expansion tank.
There is one more dangerous consequence of the considered faults
The liquid that has entered the compressor cylinders, through the gaps between the cylinder, piston and rings, seeps into the compressor crankcase and flows from it into the engine oil crankcase. Therefore, when looking for a place where coolant enters the oil, it is necessary we should also keep in mind the compressor.
Brake failures are in most cases caused by malfunctions of pneumatic drive devices.
The following are the most likely malfunctions that a driver can detect and fix without using diagnostic equipment
If the pneumatic actuator receivers are not filled, and the pressure regulator discharges air into the atmosphere, then there may be several reasons for this malfunction: the pipeline between the regulator and the protective valves is blocked; the pressure regulator is faulty - most often the filter element is clogged with oil or ice crystals (in winter).
If the receivers fill slowly and the pressure in them does not reach the nominal value (in the absence of leaks), then either the compressor or the pressure regulator is faulty.
If the receivers of a particular circuit are poorly filled, then first of all you should pay attention to the safety valve section of this circuit.
Inefficient braking of the vehicle by the service brake occurs if the drive is misaligned or the two-section brake valve is faulty.
If, during braking, the pressure in the brake chambers is nominal, then the brake mechanisms are misadjusted or faulty.
If, when braking with a service brake, the pressure is below normal only in the brake chambers of the front axle, then either the lower section of the brake valve or the pressure limiter may be faulty.
If the pressure in the brake chambers is normal, and braking is inefficient, then the cause of this malfunction may be a large stroke of the brake chamber rods or, for example, oily brake pads.
If, when the brake pedal is depressed, the braking of the wheels of the rear bogie is ineffective or does not occur at all, while the front wheels brake normally, then the upper section of the brake valve may malfunction in the pneumatic part of the drive or the brake force regulator is faulty.
In this case, there may be violations of the adjustment of the brake mechanisms or the drive of the brake force regulator.
If, after lowering the brake pedal, all the wheels of the car do not brake, the two-section brake valve may be faulty (the pusher or upper piston is jammed) or the brake valve drive is misaligned (there is no pedal free play).
If, after releasing the brake pedal, air does not come out only from the rear brake chambers, then it is possible that the brake force regulator or the upper section of the brake valve is faulty.
These malfunctions lead to a delay in the discharge of air from the front brake chambers. If, when releasing, air is not released only from the front brake chambers, then the pressure limiter or the lower section of the brake valve is faulty.
The cause of air leaks through the atmospheric outlet of a two-section brake valve can be not only sealing rings and valves in the valve itself, but also other devices of the brake system.
If a leak is observed when the pedal is released and the parking brake is on, then the brake valve is faulty.
According to the regular two-needle pressure gauge, you can accurately determine which section of the valve is leaking: if the upper arrow of the pressure gauge “falls” when the engine is not running, then the lower section of the valve is leaking; the lower arrow “falls” - the upper section is leaky.
If air leakage through the atmospheric outlet of the brake valve is observed only when the parking brake is released, and stops when it is turned on, then the trailer brake control valve with a two-wire drive or one of the energy accumulators is faulty.
You can identify a faulty device by supplying air to the power accumulators from the emergency release circuit:
- if, when the emergency release button is pressed, the leakage from the brake valve continues, then the seal of the pusher in the energy accumulator housing is leaky, and if there is no leakage, then the membrane in the trailer brake control valve is faulty.
If the wheels of the rear bogie do not release when the parking brake is released, then the parking brake valve, accelerator or dual-line valve and energy accumulators may be the cause of this malfunction.
It is possible that one of the pipes in the parking brake circuit is clogged, frozen, or pinched.
If one of the energy accumulators does not work when moving the parking brake valve handle, then the cause may be dents in the body or jamming of the pusher. It is also possible that the pipeline is blocked, through which air is carried to the idle power accumulator.
If the rods of the brake chambers come out when the energy accumulators are turned on, and the car does not brake efficiently enough, then it is necessary to check the stroke of the rods and the serviceability of the brake mechanisms and wheels.
The most common malfunctions in the parking brake circuit, as in the entire pneumatic drive, are compressed air leaks due to damage to the sealing rings cuffs.
A leaky stem seal in the guide leads to air leakage from under the parking brake valve handle when releasing the brakes.
The cause of air leakage from the atmospheric outlet of the parking brake valve is not always the leakage of seals in the valve itself.
For example, there may be a leak due to a defective 2-wire trailer brake control valve.
To determine the faulty device, fill the pneumatic drive with compressed air, turn on the parking brake, disconnect the control line from the valve.
If, at the same time, air leakage from the atmospheric outlet continues, then the parking brake valve is faulty; if a leak is observed from a disconnected pipe, then the trailer brake control valve is faulty.
If air leaks from the atmospheric outlet of the relay valve during braking and when the parking brake is released, then the sealing ring of the atmospheric outlet of the valve is leaking.
Air leakage through the atmospheric outlet of this unit when braking with a parking brake is caused by the loss of tightness of the inlet valve, and when released, the exhaust valve. In the latter case, the release of the rear wheels is not provided.
Sometimes there is air leakage through the relay valve when the parking brake is applied and the pedal is depressed at the same time. In this case, one of the energy accumulators is faulty - air from the brake chamber enters the energy accumulator through the seal of the pusher pipe and then through the accelerator valve into the atmosphere.
During operation in power accumulators, the piston seals in the cylinder and the pusher pipes in the housing wear out and fail.
When the parking brake is released, compressed air from under the piston through a leaky seal enters the cavity above the piston and through the connecting hose on the side of the device under the brake chamber membrane, and from there into the atmosphere through the drain hole. In this case, when the parking brake is applied, the leakage stops.
If the seal of the pusher pipe in the energy accumulator housing fails, then when the parking brake is applied, compressed air from under the piston enters the cavity above the membrane and escapes into the atmosphere through the brake force regulator.
If the regulator lever is in the upper position, then the air is vented to the atmosphere through the atmospheric outlet of the brake valve.
To detect a faulty energy accumulator, after releasing the parking brake, one by one disconnect the pipelines supplying compressed air to the rear brake chambers: for a faulty device, compressed air will escape from the cavity of the brake chamber.
If with the emergency release button pressed; the energy accumulators are not released (at a pressure in the pneumatic drive of more than 500 kPa), and after it is released, a small portion of compressed air comes out of the atmospheric outlet of the pneumatic valve, which means that the pipeline section between the valve and the two-line valve is blocked. If, after releasing the air outlet button, there is no atmospheric outlet, then the valve itself is faulty.
If, when the tap button is pressed, air escapes into the atmosphere through the accelerator valve, then the two-way valve is faulty.
Air leakage from the atmospheric outlet may be due to a malfunction of either the faucet itself or the dual-line valve. If air leakage is observed regardless of the position of the parking brake valve handle, then the valve itself is faulty.
But if the leak occurs only when the parking brake is released, and stops when braking, then the two-way valve is leaking
In both cases, it is forbidden to plug the atmospheric outlet in the emergency release valve with a plug, as this will cause spontaneous release of the parking brake and the vehicle's emergency brake will not work satisfactorily.
This is explained by those. that when the emergency or parking brake is turned on by turning the handle of the parking brake valve, it will be difficult or impossible to release air from the energy accumulators.
If, when the auxiliary brake valve button is pressed, the engine does not stop (the dampers in the exhaust pipes do not turn), and the trailer does not slow down, then there may be several reasons explaining this phenomenon: air is not supplied to the auxiliary brake valve, the pipeline is pinched or clogged , going from the crane to the pneumatic cylinders, the crane itself is faulty. The malfunction is determined by the sequential shutdown of pipelines.
If the fuel does not turn off when the auxiliary brake is applied, and the dampers in the exhaust pipes operate, then you should check whether compressed air is supplied to the pneumatic cylinder on the fuel pump. A malfunction is also possible in the mounting of the pneumatic cylinder.
The damper mechanism and the pneumatic cylinders that control them operate in the most unfavorable conditions. Poe That is why they fail more often than others, most often the dampers jam. If this happens with both dampers, then the engine will not start, if with one, then the engine starts, but smokes and does not develop power.
There may also be malfunctions in the damper drive pneumatic cylinders, the most common of which is the loss of tightness of the piston cuff.
The trailer solenoid switch is located on the left side member of the frame inside, next to the clutch housing.
If the sensor or electrical wiring fails and when the auxiliary brake is turned on, the trailer does not brake, and the road train may skid and fold.
If, after releasing the button of the auxiliary brake valve, the air from the pneumatic cylinders and the sensor is not released, i.e. the auxiliary brake does not turn off, then you need to check the atmospheric outlet in the valve.
In winter, it often freezes over, a mud-ice plug forms in the atmospheric outlet, which does not allow air to escape from the circuit.
If in this case the inlet valve in the auxiliary brake valve loses its tightness, the brake will automatically turn on and the engine will stop for no apparent reason.
If there is no air in the auxiliary brake circuit, the engine can be started, but after a few minutes it spontaneously stops due to air supply through a faulty valve to the fuel shut-off pneumatic cylinder.
This faucet needs to be replaced. If there is no spontaneous engine stop, but it does not start after the auxiliary brake valve button is released while the car is moving, then it is enough to clean the atmospheric outlet of the valve.