Clutch control units visible in the clutch bell of the dismantled engine
- 1 - off lever (force is exerted on it by the clutch master cylinder);
- 2 - release bearing;
- 3 - input shaft of the gearbox.
Above the clutch pedal (figure «1» marked lever) visible rubber cuff (5) clutch slave cylinder and both mounting bolts (3 and 4). Numeric «2» the locking collar of the hinge pin is indicated, which must be removed during dismantling.
Order of execution
1. If the clutch disengages correctly, its hydraulic system is fine anyway.
2. But if it turns off badly or the pedal fails without resistance, then air must have entered the hydraulic system.
3. Simply removing air will not help here - you need to find the leak and repair it. Now you can remove air from the system. Information on other causes of clutch failure can be found at the end of this chapter under Help with malfunctions.
4. For the purpose of a preventive check of the hydraulic clutch system, look for traces of brake fluid on the working cylinder (at the top of the clutch pedal) and on the master cylinder (on the gearbox).
5. Oil-soaked clutch cylinders are leaky and must be replaced. Although the origin of oily dirt on the master cylinder is difficult to determine without a thorough cleaning of this area.
Tip: Clutch hydraulics get their fluid from the brake fluid reservoir, but there is no danger to the brake system if there is a leak in this area. The fluid intake pipe for the hydraulic clutch system is located quite high on the reservoir, so there is always a sufficient amount of fluid for the brakes.
Removing the clutch slave cylinder
1. Suck out as much fluid as possible from the expansion tank (with a large medical syringe).
2. Dismantle the trim of the dashboard at the bottom left (chapter Salon).
3. Place an old rag under the working cylinder, disconnect the supply hose and allow the rest of the liquid to drain into the rag.
4. From the side of the engine compartment, unscrew the pressure hose to the master cylinder.
5. Unscrew two fixing bolts with internal hexagons at the working cylinder.
6. Fold back the hinge pin locking collar (connecting pedal and working cylinder), squeeze out your finger.
7. Now you can remove the cylinder.
8. When installing a new cylinder, the rod that presses the piston of the working cylinder must be adjusted so that the clutch pedal is about 10 mm higher than the brake pedal.
9. Be sure to check: the return spring must depress the pedal properly. In this case, the pedal in the rest position should not rest at the top of its bracket. Otherwise, the piston of the working cylinder in the rest position will not be able to move to the rear stop.
10. To adjust, loosen the jam nut on the push rod and turn the push rod left or right around its axis. Then tighten the locknut again.
11. Bleed the hydraulic clutch system.
Tip: The clutch pedal in the Audi A4 is equipped with a so-called top dead center spring. It helps when you press the pedal, but after removing the foot returns it to its original position. If the pedal does not return back, then air or hard travel of the pedal or spring has entered the hydraulic system.
Removing the clutch master cylinder
1. Raise and secure the front left side of the vehicle.
2. Unscrew the pressure hydraulic hose from the master cylinder - be careful, brake fluid flows out.
3. Substitute a container.
4. Loosen the mounting bolt on the cylinder, remove the master cylinder back from the gearbox housing.
5. If necessary, help yourself with anti-corrosion spray and pry bar.
6. Lightly oil the surface of the body of the new cylinder, lubricate the tappet with MoS2 paste.
7. Insert the master cylinder into the gearbox housing and press it in until you can screw the mounting bolts into the threads on the gearbox (25 Nm).
8. Bleed the hydraulic system.
Bleeding the hydraulic clutch system
Anyone who does not have the usual workshop air bleeder bleeds the hydraulic clutch system in the same way as a brake system - almost without error - in the following way:
1. Open the bleed valve on the front wheel brake and the valve on the clutch master cylinder about 1.5 turns each.
2. Connect both nipples with a hose.
3. Now depress the brake pedal slowly and carefully several times to force the hydraulic fluid from the front wheel brake through the clutch hydraulics.
4. Do not press the pedal with force, otherwise the hose will break!
5. Keep an eye on the fluid level in the expansion tank.
6. If air bubbles no longer enter the expansion tank from the hydraulic clutch system, then both nipples are screwed in and the hose is removed.
7. Check the brake fluid level!
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