Here's a breakdown of how the clutch system works and the likely culprits:
How a Hydraulic Clutch System Works:
1. Clutch Pedal: Pressing the clutch pedal pushes a piston in the master cylinder.
2. Master Cylinder: This is a hydraulic cylinder located near the clutch pedal. It's filled with brake fluid (or sometimes a specific clutch fluid). The piston's movement pushes fluid through a line.
3. Slave Cylinder: The fluid travels through a hydraulic line to the slave cylinder, located near the transmission.
4. Slave Cylinder Piston: The fluid pressure in the slave cylinder pushes a piston that is mechanically linked to the clutch fork.
5. Clutch Fork: This fork moves the throw-out bearing.
6. Throw-Out Bearing: This bearing presses against the pressure plate, separating the clutch disc from the flywheel, allowing you to shift gears. Releasing the clutch pedal reverses this process.
7. Leak or Low Fluid: If there's a leak in the hydraulic line, a failing master cylinder, or a failing slave cylinder, the system will lose pressure. With the engine running, the vacuum assist (explained below) might compensate partially; without the engine running, this compensation disappears and you'll have to use more force to disengage the clutch which you can manage when the car is not running.
Why it might only work with the engine running:
* Low Clutch Fluid: Check the master cylinder reservoir for fluid level. If it's low, there's a leak somewhere in the system. This is the most common cause.
* Leaking Master Cylinder: The master cylinder seal could be worn, leaking fluid internally or externally.
* Leaking Slave Cylinder: The slave cylinder could have a leak, preventing it from building sufficient pressure to disengage the clutch. This is more challenging to detect visually, you usually need to diagnose with a pressure test.
* Air in the Hydraulic Line: Air in the lines can compress, leading to inconsistent clutch engagement. Bleeding the clutch hydraulic system can resolve this, however often it indicates another fault causing fluid to leak.
* Vacuum Assist (Possible, but less likely on a '96 Saturn SL): Some cars use vacuum assist to make the clutch pedal easier to press. However, a failed vacuum assist on its own is unlikely to fully prevent the clutch from disengaging. A leak in the vacuum line or a bad vacuum booster would be more likely cause related symptoms but not this specific one.
What to do:
1. Check the Clutch Fluid Level: This is the first and easiest thing to check. Top it off if low, but a significant drop indicates a leak somewhere in the system.
2. Inspect the Hydraulic Lines: Look for any visible leaks or damage to the hydraulic lines running from the master cylinder to the slave cylinder.
3. Listen for Leaks: With the engine off, slowly pump the clutch pedal. Listen carefully for hissing sounds, which might indicate a leak in the system.
4. Consider professional help: Clutch hydraulic system repair requires some mechanical expertise. If you're not comfortable working on your car, it's best to take it to a qualified mechanic for diagnosis and repair. They'll be able to pressure test the system and pinpoint the exact location of the leak.
Unfortunately, I can't provide a picture. A diagram would be complex, but you can easily find diagrams and videos showing how a hydraulic clutch system works by searching "hydraulic clutch system diagram" or "how a clutch works" on Google or YouTube. Those visual aids will greatly improve your understanding.
