Removing air from the ZIL-5301 clutch control system

The hydraulic system of the clutch control mechanism consists of a master cylinder, a slave cylinder with a pneumatic booster, a flexible hose and a pipeline

To prevent leakage of working fluid and the entry of air into the hydraulic system, it is necessary to carefully monitor the tightening of all threaded connections of the system.

If the hydraulic system leaks (air gets in and air pockets form), it must be sealed and re-pumped.

It should be remembered that it will be impossible to bleed the system if there is no free play of the master cylinder piston pusher, since the pusher and piston are a shut-off valve through which the hydraulic system is replenished with liquid as necessary, and if there is no free play of the pusher it will permanently closed.

The same thing happens when the pedal gets stuck and its release spring is unable to lift it to its highest position.

Bleeding can be carried out either with or without compressed air in the system.

Clutch drive: 1 - lower pedal stop; 2 - pedal; 3 - tension spring; 4 - movable stop (adjusting bolt); 5 - eccentric finger; 6 - hydraulic drive tube; 7 - bypass valve; 8 - air supply hose to the amplifier; 9 - hydraulic drive hose; 10 - pneumohydraulic booster; 11 - coupling bolt; 12 - clutch release fork; 13 - clutch release fork lever; 14 - spring; 15 - cabin front panel; 16 - main cylinder; 17 - master cylinder reservoir; 18 - finger: 19 - pusher fork; 20 - lock nut; 21 - pusher; A - free stroke of the pusher, corresponding to the free stroke of the clutch; C - full travel of the clutch pedal; D - the amount of protrusion of the end of the pusher from the threaded hole of the fork

To do this you need to do the following.

1. Unscrew the cap of the master cylinder reservoir, remove the cap reflector, and then fill the system with working fluid to a level not lower than 15...20 mm from the top edge of the reservoir.

The system should be filled with working fluid using a strainer to prevent foreign impurities from entering the system.

2. Remove the rubber cap from the bypass valve located in the upper part of the rear housing of the CCGT unit and place the hose for bleeding the hydraulic drive onto the valve head.

Dip the free end of the hose into the working fluid, poured to 1/3 of the height of a transparent vessel with a capacity of approximately 0.5. Work is accelerated if there is a check valve at the end of the hose.

3. Unscrew the bypass valve 1 turn and successively press the clutch pedal all the way to the lower pedal stop at intervals between presses of 1-3 s until the release of air bubbles from the working fluid flowing through the hose into the glass vessel stops.

While pumping the system, make sure that the level of working fluid in the master cylinder reservoir does not fall below 35 mm from the edge. This will eliminate the possibility of air entering the system and will allow the line to be replenished with working fluid.

If necessary, periodically add fluid.

With the clutch pedal pressed all the way, the bypass valve should be screwed in tightly. Then remove the hose from the valve head and put on the rubber cap.

The bleeding process can be somewhat accelerated if, after each press, without releasing the pedal, you close the bypass valve and only then release the pedal.

Usually, after the third press, liquid without air bubbles begins to flow from the bypass valve.

  • 4. After bleeding the system, add fresh working fluid to the master cylinder reservoir to the level specified in step 1, install the plug reflector and tighten the tank plug.
  • 5. Wipe the surface of the hydraulic drive parts.
  • 6. Check the quality of pumping by the full stroke of the PSU piston pusher; to do this, press the clutch pedal until it stops against the lower travel stop.

With a correctly adjusted clutch control mechanism and a fully pumped hydraulic system, the stroke of the PSU piston pusher should be 27-28 mm.

The air pressure in the car’s pneumatic system must be at least 0.55 MPa.

At lower pressures, compressed air does not flow to the CCGT and the force on the clutch pedal increases sharply, but the performance of the drive is not lost.

If the pusher stroke is less than specified, and the system is working properly and Since the clutch control mechanism is correctly adjusted, you should continue bleeding, as indicated above, until the air is completely removed from the system and the proper pusher stroke is obtained.

The hydraulic system of the clutch control mechanism uses 0.4 liters of Neva brake fluid as the working fluid.

The use of other liquids is unacceptable, as it will lead to swelling of the rubber cuffs and seals and failure of the clutch control mechanism.

Care should be taken when handling brake fluid, as it is poisonous.

Brake fluid getting on the plastic lining of the thermal and noise insulation in the cabin causes its destruction.

Care should be taken when filling the brake system and clutch hydraulic drive with fluid.

If liquid gets on the plastic lining, remove the liquid immediately