Brake mechanisms - drum type with two inner shoes and an easily removable brake drum

On vehicles equipped with ABS, special holes are made in the brake pads of the rear axle (opposite the return spring hooks) to allow the removal or replacement of the brake pads without disassembling the wheel drive.

Maza brake adjusting lever (ratchet)

At the end of the expander shaft, there is a worm-type adjusting lever (fig. 1) connected to the brake chamber rod.

By turning the worm 3 by the hexagonal head of the axle with a key, you can turn the expanding fist, and, consequently, spread the brake pads, thereby reducing the gap between them and the drum.

In order to rotate the axis, plate 7 must be released and moved up.

On cars, an adjusting lever with a built-in automatic regulator can be installed (Fig. 2).

Auto brake adjuster

To prevent grease from entering the brake mechanisms, rubber o-rings are installed in the brackets of the expanding cams of the front and rear brakes.

Brake chambers - diaphragm, designed to actuate the brake mechanisms of the front wheels of the car when the service brake system is turned on.

MAZ brake chamber

Brake chambers with spring energy accumulators (Fig. 3) are designed to actuate the brake mechanisms of the wheels of the rear and middle axles when the working, parking and spare brake systems are turned on.

When the service brake system is turned on, the brake mechanisms are actuated by rods of 10 diaphragm brake chambers, the device and principle of operation of which practically does not differ from the front brake chambers (supply 11).

When the parking brake system is turned on, compressed air is released from the cavity under the piston 6, which, under the action of the power spring 7, moves down and moves the pusher 4, the latter through the thrust bearing 9 acts on the diaphragm 3 and the rod 10 of the brake chamber, resulting in the vehicle braking .

When the parking brake system is turned off, compressed air is supplied under the piston 6 through the supply 12, which, together with the pusher, moves upward, compressing the spring and allowing the brake chamber rod to return to its original position under the action of the return spring 1.

When braking with the spare system, air is partially released from the cylinders of the energy accumulators, to the extent of the required braking efficiency of the vehicle, which corresponds to the intermediate positions of the control valve handle.

Thus, the braking efficiency depends on the angle of rotation of the crane handle.

Spring-loaded brake chamber

It is possible to install diaphragm brake chambers with a spring-loaded energy accumulator and a quick-release device on a car (see Fig. 4).

The quick-release device (BRU) is a spring-loaded fixing sleeve 9, which connects the diaphragm 5 with the rod 4 of the energy accumulator through the balls 8.

The camera is released as follows: remove the cover, insert the pusher 12 (located in the spare parts box) as far as it will go into the fixing sleeve 9 and press or lightly hit with a hammer.

In this case, the sleeve 9 moves, the balls 8 come out of the groove on the rod 4, the diaphragm 5 under the influence of the spring 11 moves all the way into the body, the spring 1 moves the rod 4, releasing the wheel brake mechanism.

MAZ brakes

When compressed air is supplied to the cavity "A", the balls 8 fall into the groove of the rod 4 and are fixed by the sleeve 9, while the energy accumulator is blocked.

It is strictly forbidden to disassemble spring energy accumulators yourself!

The brake mechanism of the main parking brake system of MAZ-631705, 631708, 642505, 642508, 533605 vehicles is drum (Fig. 5), double servo-action shoe with lever unclamping of the shoes and a clearance adjustment mechanism.

It is attached to the transfer case housing, the brake drum is attached to the transfer case output shaft flange.

MAZ parking brake actuator

The action of the brake is as follows.

When braking and the force from the drive cable is transmitted to the drive lever 9, which, through the intermediate lever 17 and the earring 8, acts on the lever 7 of the shoe.

When the drum rotates counterclockwise, the driving force from the shoe lever through the rod 3 is transmitted to the left shoe 22 and presses it against the brake drum.

At the same time, due to friction, the shoe is captured by the drum and shifted in the direction of rotation, pressing through the adjusting device on the right shoe 16, and presses it against the drum.

When the brake drum rotates clockwise, the lever 7 of the shoes, resting on the rod 3, transfers the drive force to the right shoe 16 and presses it against the drum.

Due to friction, the shoe is captured by the drum and shifted in the direction of rotation, pressing through the adjusting device on the left shoe 22, and presses it against the drum.

MAZ parking brake control lever

The drive circuit is shown in fig. 6, the design of the control lever is shown in fig. 7.

Auxiliary brake system mechanism

Auxiliary brake system mechanism (Fig. 8) throttle type with dampers installed in the engine exhaust pipe in front of the muffler.

The mechanism consists of a body and shutters 2, fixed on the axis 3.

A rotary lever 4 is also fixed on the damper axis, connected to the rod of the actuator pneumatic cylinder.

The lever 4 and the shutters 2 associated with it have two fixed positions.

When the auxiliary brake is turned off, the damper is installed along the exhaust gas flow, and when turned on, it is perpendicular to the gas flow, creating backpressure at the outlet.

At the same time, the fuel supply is cut off using a pneumatic cylinder connected to the engine stop bracket.

Engine brake air cylinder

Pneumatic cylinder (Fig. 9) is designed to control the dampers of the auxiliary brake system mechanism.

When the auxiliary brake system is turned on, compressed air enters the over-piston space and, overcoming the resistance of the return springs, moves the piston and rod 8, which is connected to the mechanism damper control lever.

The piston returns to its original position under the action of a return spring.

Brake adjustment

Brake valve drive

In the brake valve drive (Fig. 10), the angle of 45°+2° is adjusted by bolt 2. After adjusting nut 3, tighten to a torque of 11.8—15.7 Nm. Pedal free play should be 17-27 mm.

The adjustment is made by changing the length of the stem 4. After adjusting the nut 5, tighten the torque to 23.5—35.3 Nm.

When installing the adjusting lever (Fig. 1), the stroke of the brake chamber rods must be within 25-40 mm. When the stroke of the rods is increased to 45 mm, the brakes must be adjusted. In this case, the difference in the course of the rods of the brake chambers on each axle should not exceed 8 mm.

Adjust the brake mechanisms in the following order:

  • —jack up the wheel;
  • - loosen the bolt 6 and slide up the locking plate 7 of the expansion knuckle adjusting lever; - by rotating the worm 3 (at the same time, the rod of the brake chamber should not move from the chamber), spread the brake pads until they touch the working surface of the drum;
  • - turn the worm in the opposite direction by about 1/3-1/2 turn, lock the worm axis by sliding the plate to its original position and securing it with a bolt;
  • —check that the stroke value of the rod is within acceptable limits;
  • — check that the drum does not hit the shoes in the disengaged position.

Check the stroke of the brake chamber rods at an air pressure in the pneumatic system circuits of 0.56±0.04 MPa (5.6±0.4kgf/cm2). When measuring, the lever of the brake force regulator must be turned up to the maximum angle allowed by the design.

When installing the adjusting lever (Fig. 2), the stroke of the brake chamber rods must be within 38.. .44 mm. The stroke of the rods is not adjusted during operation.

After replacing the linings, as well as when replacing the adjusting lever or the brake chamber, it is necessary to adjust the stroke of the brake chamber rods.

For this:

  • - install the adjusting lever on the expander shaft so that the distance from the brake chamber fork to the lever is 20-80 mm.

In this case, the lever should be located with the plug forward along the stroke of the brake chamber rod at toruscan, but with the hexagonal end of the worm shaft to the brake chamber (when replacing on the rear axle, the brake chambers with spring energy accumulators must be disengaged);

  • - by rotating the hexagonal end of the worm shaft counterclockwise, while clicking the reverse clutch should be felt, align the holes of the fork of the camera rod and the lever and connect the lever with the fork with your finger.

In this case, the shaft of the expanding fist must remain in its original position under the action of the coupling spring of the shoes;

  • — turn the lever leash to the stop (in the direction of rotation of the lever during braking) and fix the latch in this position;
  • — adjust the stroke of the brake chamber rod by sequentially pressing the brake pedal to the stop at a compressed air pressure in the system of 600 kPa (6 kgf / cm2) at least until a constant value of the rod stroke is established within 38-44 mm.

Caring for the adjusting lever (Fig. 2) consists in periodically lubricating it through a grease fitting 18 until the grease exits the safety valve 19.

During operation, periodically control the operation of the levers by measuring the stroke of the camera rod.

The stroke difference of the rods should not exceed 5 mm.

If an increased code is found, check the correct installation of the lever or find out the cause of the malfunction and eliminate it, for which purpose disassemble the lever with cleaning and flushing of the parts.

Disassembly is done in the following order:

  • — unscrew the plug 6, having previously unlocked it;
  • —remove spring 5 with coupling half 3;
  • —remove cover 12 with driver 13 and control ring 14 as an assembly and gasket 17, pusher 2;
  • —remove worm 7 with coupling half 4 as an assembly;
  • —remove gear 15.

Assemble the lever in the reverse order. Screw plug 6 up to the stop with a torque of 2-3 Nm (0.2-0.3 kgf-m) and unscrew it by 15-20 °, having previously lubricated the thread with sealant.

Lock the cap by pulling the shoulder into the groove of the body. Lubricate the lever through the grease fitting 18 until the grease exits the valve 19.

Adjusting the parking brake

As the parking brake pads wear, the clearance between the brake pads and the brake drum must be adjusted. For this you need:

  • — hang out the wheels of the middle axle (or one of the wheels);
  • — set lever 1 (see Fig. 6) to the “disengaged” position, while lever rail 5 (see Fig. 5) must be in the front end position (the parking brake warning light must go out);</li >
  • —remove the return spring 9 (see Fig. 3), unscrew the nut 5, unscrew the coupling 4 from the rod 6;
  • - remove the rubber plug 14 (see Fig. 5) from the caliper 11. Using a screwdriver, catching the tooth on the tooth of the sprocket nut 21, from the bottom up, tighten the sprocket nut so that the drum does not turn from the effort of the hands;
  • - unscrew the sprocket nut in the opposite direction so that the brake drum rotates freely without hitting the brake pads (check the free rotation of the drum after pressing the lever 9 towards the bracket 1 by hand and returning it to its original position);
  • - put in place the stub 14;
  • — turn the lever 9 (see Fig. 5) towards the bracket 1, bring the shoe release lever 7 to the stop in the bar 3 without releasing the shoes;
  • — screw the coupling 4 (see Fig. 6) onto the rod 6, ensuring the tension of the rope 3;
  • —lock nut 5;
  • — install return spring 9;
  • —remove the car from the jack.

After adjusting at the maximum stroke of the rail 5 (see Fig. 7) of the lever 1 (see Fig. 6), the stroke of the lever 9 (see Fig. 5) should not exceed 40 mm, and the brake drum in the braked state should not touch the brake pads.

If the lining of the brake pads is worn out so that the above adjustment does not achieve the effectiveness of the parking brake, it is necessary to remove the lever 9 (see Fig. 5) from the shaft 18, having previously removed the retaining ring, rearrange the lever 9 on the slots in the direction from the bracket 1, install the retaining ring and adjust the parking brake.

The design of the brake mechanisms provides for an easily removable brake drum and the ability to visually determine the condition of the brake linings through hatches in the shields.

To replace worn pads, jack up the wheel, remove the tire and, unscrewing the nuts, remove the disc from the bolts 16.

Then, screw two M16 dismantling bolts 40 ... 60 mm long into the dismantling threaded holes of the drum 10 and remove the drum by evenly screwing in the bolts.

After that, remove the coupling springs, unscrew the bolts 8 and, having removed the pads 15 from the expanding fist 14, remove them from the axles 12.

After replacing the worn pads with new ones, reinstall the pads in reverse order. When installing the pads, lubricate axles 12 with Litol-24 grease.

To facilitate the removal of the brake drum, as well as when replacing the machine static adjusting lever, to increase the gap between the shoes and the drum, it is allowed to unscrew the plug with a 1/8” thread from the lever body, use a thin screwdriver to disengage the ratchet connection of the movable coupling half 4 (Fig. 2) and turn the worm axis 7 by the hexagon clockwise by a few turns, then reinstall the plug.

After installing the brake drum, it is necessary to adjust the stroke of the brake chamber rod, as described above

When replacing only the pads, the pads assembled with the pads must be machined in pairs along the outer diameter to the nominal size, if the drum was not bored to the repair size.

If the drum was bored to the oversize, then the pads must be machined to the same oversize number.

It is forbidden to install on the same axle and in the brake mechanism brake pads with pads that have a different code (designation) on the side surface of the pads.