Table of contents: Removal the clutch master cylinder ↓ Removal the clutch slave cylinder ↓ Bleeding the hydraulic clutch drive ↓
If the clutch disengages correctly, then the hydraulic clutch drive is also OK in any case.
If the clutch does not separate well or the pedal falls without resistance, then it is clear that air has entered the hydraulic drive. Simply removing the air in this case will not help - you should find and repair the leaky place. After that, you can start removing the air. Other reasons why the clutch does not separate correctly are indicated in the list of faults at the end of the chapter.
Anyone who wants to check the hydraulic clutch drive just in case should look for brake fluid leaks on the master cylinder (at the top of the clutch pedal) and in the working cylinder (near the gearbox).
Clutch cylinders that are wet with oil are leaky and should be replaced. However, without a thorough cleaning of the area around the slave cylinder, the origin of the oil stain on it can be very difficult to determine.
Removal the clutch master cylinder
Remove as much fluid as possible from the brake fluid reservoir (for example, with an old syringe).
Unscrew the shelf on the left under the dashboard (chapter "Salon").
Remove the heating hose located underneath (one screw, one bracket).
Remove the supply hose and allow the remaining liquid to drain into a rag.
In the engine compartment, to the left of the brake booster, unscrew the pressure hydraulic line to the working cylinder.
Remove the two Allen bolts securing the master cylinder
Pry up the lock washer of the pivot pin (pedal/master cylinder connection), squeeze out a finger.
Now you can remove the cylinder.
When installing a new cylinder, the rod that presses on the master cylinder piston should be adjusted so that the clutch pedal is located approximately 10 mm above the brake pedal.
It is important to note that the return spring must return the pedal correctly. At the same time, the pedal in the initial (resting) position should not rest against the pedal block bracket.
To adjust, loosen the lock nut on the push rod and turn the rod left or right around its own axis. Then tighten the lock nut again.
Remove air from the hydraulic clutch drive (bleed).
Note: The clutch pedal in the Audi 100 is equipped with a spring located above the dead center. It helps when pressing the pedal, but after releasing the pedal, it presses it back to its original position. If the pedal does not return, this means that air has entered the hydraulic drive or the pedal bearings or spring are seized.
Removal the clutch slave cylinder
Raise and support the left front side of the vehicle.
Unscrew the pressure hose of the hydraulic drive of the working cylinder - be careful, brake fluid will leak out and must be collected.
Loosen the mounting bolt on the cylinder and pull the slave cylinder out of the gearbox housing in a rearward direction.
If necessary, use rust remover spray and a pry bar.
Lightly lubricate the new cylinder along the unpainted walls of the housing, apply MoS₂ paste to the drive pusher.
Insert the slave cylinder into the gearbox housing and press it in until the mounting bolt can be screwed into the thread on the gearbox housing (25 Nm). Use only the special bolt with a rotating tip.
Bleed the hydraulic clutch drive.
Bleeding the hydraulic clutch drive
If you do not have the device usually used for this purpose in a workshop, you can bleed the clutch using the same method as the brake system (chapter "Brake system") or, almost without loss, in the following way:
Open the bleed valve of one of the front wheels and the valve of the clutch hydraulic drive slave cylinder each by approximately one and a half turns.
Connect both valves with a hose.
Now press the brake pedal slowly and carefully several times so that the brake fluid from the front brake is forced into the hydraulic clutch drive.
Do not press too hard, otherwise the hose may come off!
Monitor the brake fluid level in the reservoir.
If air bubbles from the clutch hydraulic system no longer rise from the brake fluid reservoir, then you can close both valves and remove the hose
Check the brake fluid level!