Design, malfunctions and maintenance of brakes GAZ-66, GAZ-53

The GAZ-53A and GAZ-66 vehicles are equipped with drum-type brakes with a hydraulic drive and a hydraulic vacuum booster

The brakes of the front and rear wheels of the GAZ-53A are identical in design and differ only in size.

The rear brakes of the GAZ-b6, unlike the brakes of the GAZ-53A, do not have protective screens on the brake cylinders, but have rear pads with long linings.

The front brakes of the GAZ-66 have two cylinders, each of which acts on its own pad.

The design of the brakes is shown in Fig. 1 and 2. The action of the hydraulic vacuum booster is based on the use of vacuum in the engine suction pipe.

The amplifier consists of a vacuum chamber, a hydraulically driven vacuum control valve and a hydraulic cylinder.

All these parts are combined into one hermetically sealed unit, which is mounted on two brackets on the longitudinal beam of the frame.

The vacuum chamber of the amplifier is connected to the engine suction pipeline through a pipeline and a plate shut-off valve.

The shut-off valve is installed in close proximity to the vacuum source, thereby maintaining maximum vacuum in the amplifier system.

Brake Maintenance

Adjusting the gap between the pads and drums. The brakes should be adjusted when the brake drums have cooled down and the wheel bearings are correctly adjusted.

There are two brake adjustments: current and full

Current adjustment. As the friction linings of the brakes wear out, the gaps between the linings and the brake drums increase, and the pedal begins to approach the cabin floor when braking.

Current brake adjustment restores the original clearances between the friction linings of the pads and the brake drums, compensating for lining wear.

To adjust the brakes you need:

• - hang the wheel using a jack;
• - rotating the wheel forward, slightly turn the pad eccentric in the direction of the arrows shown in Fig. 1 and 2 until the block brakes the wheel;
• - gradually lower the eccentric, turning the wheel by hand in the same direction until the wheel begins to rotate freely;
• - install the second pad in the same way as the first, while rotating the wheel forward for the front brake of the GAZ-66 car and backward for the rear brake of the GAZ-66 car and all brakes of the GAZ-53A car.

After adjusting the brake pad clearance, check the operation of the brakes on the road.

Full adjustment. Wheel brakes should be fully adjusted when changing friction linings, pads or after machining the drums.

When fully adjusting the brakes, you must:

• - hang the wheel using a jack;
• - slightly unscrew the nuts of the support pins and set the support pins of the pads to the initial position;
• - pressing the brake pedal with a constant force of 12-16 kg, turn the support pins in the direction indicated by the arrows so that the lower part of the lining rests against the brake drum.

The moment when this happens is determined by the increase in resistance when the support pin rotates. Tighten the support pin nuts in this position;

• - turn the adjusting eccentrics so that the pads rest against the brake drum;
• - release the brake pedal;
• - turn the adjusting eccentrics in the opposite direction so that the wheel rotates freely;
• - adjust the brakes of all wheels in this way.

After adjusting the pad clearance of all brakes, check the operation of the brakes on the road.

With correctly adjusted gaps between the shoe linings and the drums, the brake pedal, when fully braking, reaches should not go down more than ⅔ of the full stroke.

If, after adjustment, while the car is moving, the brake drums heat up slightly (the hand is comfortable when touching the drum rim), then after several braking the pads will break in and the heating will stop.

If the drums are very hot, you need to find the pads touching the drums and use the adjusting eccentrics to slightly move them away from the drums.

Adjusting the gap between the pusher and the master cylinder piston

The clearance between the pusher and the master cylinder piston is necessary to prevent spontaneous braking of the car.

If the edge of the sealing collar covers the compensation hole 23 (Fig. 3), then the brakes will not completely release the brakes, since some of the fluid cannot flow from the working part of the cylinder into the reservoir after the end of braking.

The gap should be 1.5-2.5 mm, which corresponds to 8-13 mm of pedal free play, measured in the middle of the foot pad.

To measure the gap, you need to change the length of the pusher.

The procedure for adjusting the gap on a GAZ-53A car is as follows:

• Disconnect the pedal and pusher, unscrew and remove the pin.
• Check the position occupied by the pedal under the action of the release spring.
• The pedal should rest against a rubber buffer mounted under the inclined floor of the cabin.
• Screw (or unscrew) the pedal rod into the piston pusher so much that the axis, when rolling in the master cylinder piston, is shifted back and does not reach the axis of the pedal hole by 1.5-2.5 mm. Without disturbing this position, securely lock the pedal connecting rod with the lock nut.
• Align the hole in the connecting rod and the pedal, place the pin and secure it with a cotter pin. Check the pedal free play.

The procedure for adjusting the gap on a GAZ-66 car is as follows:

• Disconnect the intermediate lever and the pusher by removing the eccentric axle.
• Check the position occupied by the pedal under the action of the tension spring. The pedal should rest against the shelf of the bracket with a rubber buffer.
• Install the master cylinder piston pusher until it stops in the piston in its rearmost position.
• Connect the intermediate lever and the master cylinder piston pusher with an eccentric axis, without changing their relative position.
• Rotate the eccentric axis in any direction to such an angle as to ensure a clearance between the pusher and the piston equal to 1.5-2.5 mm.
• Insert the washer and tighten the eccentric axle nut.
• Check the free play of the brake pedal (8-13 mm).

Brake malfunctions and how to fix them

Causes of malfunction (Methods of elimination)

The brake pedal touches the floor of the cab:

- Increased clearances between brake drums and friction linings

Adjust the brakes using adjusting eccentrics

If the friction linings are heavily worn (0.5 mm left to the rivet heads), replace them with new ones and perform a full brake adjustment

- Incorrect installation of brake pads

Perform a full brake adjustment

- Presence of air in the system

Bleed the system

- Liquid leakage in the piping system

Inspect the entire brake system and identify leaks

If after tightening the joints the leakage does not stop, replace the defective parts with new ones

- Fluid leakage from the wheel cylinders or sealing cuffs of the hydraulic vacuum booster rod

Replace damaged cuffs, repair damage to cylinders or rod

- Insufficient fluid level in the master cylinder

Add the required amount of liquid

- Fluid leakage through the inner cuff of the master cylinder

Replace the inner cuff with a new one

The brakes do not release:

- No gap between the pusher and the master cylinder piston

Adjust pedal free play

- Clogged compensation brake master cylinder holes

Clean the compensation hole with soft wire Ø 0.6 mm

replace the brake fluid if it is contaminated by flushing the entire system with alcohol

- Swelling of rubber cuffs due to mineral oil or any other liquid of petroleum origin getting into the system

Drain the brake fluid, disassemble all cylinders, wash their parts in alcohol

Flush the brake system

Replace brake seals

Before assembling, lubricate the cylinder parts with brake fluid

- Jamming of the hydraulic brake booster cylinder piston

Rinse the system with alcohol and replace the fluid.

If the defect is not eliminated, remove the amplifier, check the condition of the working surfaces of the cylinder, piston and, if necessary, replace damaged parts

- Sticking of the hydraulic brake booster control valve piston when returning to the lower position after stopping pressing the pedal

Remove the control valve, wash its piston and cuffs, as well as the hole in the cylinder with alcohol

Replace damaged cuffs or the spring if, when compressed to a height of 17 mm, it does not provide a load of 2.5 + 0.5 kg

One brake does not release:

- The tension spring of the brake pads is weakened or broken

Replace the spring if it, stretched to a length of 227 mm, does not provide a load of 34-39 kg.

- The block rotates tightly on the support pin or gets stuck in the guide bracket

Identify the cause of the jamming and lubricate the sliding surfaces of the parts so that the lubricant does not get on the friction linings

- Piston stuck in the wheel cylinder due to corrosion or clogging

Disassemble the cylinder, wash the parts with alcohol.

If necessary, clean the surface of the cylinder with fine-grained sandpaper No. 100.

Before assembling the parts, lubricate the parts with brake fluid

When braking, the car pulls to the side:

- Oiling of the friction linings of one of the brakes or two brakes on one side

Wash the linings with gasoline and sand with sandpaper

• - The fastening of one of the brake shields or two shields on one of the sides is loose
• - Uneven tire pressure on left and right wheels

Tighten the bolts securing the shield(s) and adjust the gaps between the pads and drums, bring the tire pressure to normal

High pedal force due to a malfunction of the hydraulic vacuum booster or its system:

- Leaks in the connections of the vacuum pipeline 

Eliminate leaks in pipeline connections

- Amplifier air filter clogged

Wash the filter in gasoline, moisten it with oil and put it in place

- Amplifier chamber diaphragm is torn

Disassemble the amplifier chamber and replace the diaphragm