The clutch hydraulics use DOT 3 brake fluid. Here is the GM recommended way to bleed the clutch.
1. Fill the master cylinder reservoir with new brake fluid.
2. Raise the vehicle.
3. Remove the clutch slave cylinder.
4. Hold the slave cylinder at a 45 degree angle with the bleeder at the highest point, depress the clutch pedal and open the bleeder.
5. Close the bleeder and release the clutch pedal.
6. Repeat 4 and 5 until there is no more air in the clutch hydraulic system.
Check and refill master cylinder as required during bleeding to prevent the entry of air into the system.
Be aware the C4 clutch is a bitch to bleed all the air out!!!! My mechanic finally gave up and I drove the car with a spongy clutch pedal, although it worked ok. On the 5th morning, the clutch pedal got hard and has been ok since. I would recommend a pressure bleeder on the master cylinder. If you do it as directed, have someone push hard on the clutch and open the bleeder wide to allow rapid fluid movement to move the air along. I personally think it best to supply fluid into the open bleeder and pull a vacuum at the master cylinder because air naturally wants to move to the highest point in the sytem, it doesn't want to move downward ANYWHERE in the system!
