* The master cylinder: This is located in the engine compartment and pushes hydraulic fluid to the slave cylinder. A failing master cylinder will result in a clutch pedal that feels spongy or goes to the floor.
* The slave cylinder: This is located on the transmission and actuates the clutch release fork. A failing slave cylinder may cause the clutch to not disengage properly.
* The hydraulic lines: Leaks in the lines will lead to a loss of hydraulic pressure and clutch failure.
* The clutch itself (pressure plate, disc, throwout bearing): These are internal to the transmission and require transmission removal to replace. Symptoms include slipping, difficult engagement, or noise.
Before you start taking anything apart, be absolutely certain of what you're doing or get it looked at by a qualified mechanic. Improperly working on a hydraulic clutch system can be messy and dangerous. You risk injuring yourself and damaging your vehicle significantly.
If you're having clutch problems, describe the symptoms (e.g., pedal goes to the floor, clutch slips, noisy clutch, etc.) and we may be able to offer more specific advice, but always prioritize professional help if you are unsure.