* Clutch Disc/Pressure Plate Failure: This is the most likely culprit. A worn-out or damaged clutch disc might not be fully disengaging, even though the hydraulics are working. The friction material could be glazed, worn thin, or broken. A warped or faulty pressure plate could also prevent proper disengagement. This often manifests as the clutch "grabbing" at the top of the pedal's travel or not disengaging completely.
* Throwout Bearing Failure: While less likely given the pedal's behavior, a failing throwout bearing (also called a release bearing) could be sticking or binding, preventing the pressure plate from fully releasing the clutch disc. It would be more likely to cause noise and clutch drag than the pedal simply staying down, however.
* Broken Clutch Cable (if applicable): While you mentioned replacing the hydraulic components, some older vehicles use a clutch cable instead of a hydraulic system. A broken or frayed cable would prevent the clutch from disengaging. However, the pedal behavior described (staying down) seems inconsistent with this.
Troubleshooting Steps:
1. Check for Leaks (again): Double-check your master and slave cylinder replacement. Even with new parts, improper installation could lead to leaks, which could explain the symptom (though less likely given the pedal remains down).
2. Inspect the Clutch Cable (if present): If your vehicle uses a cable, visually inspect its condition for fraying or breakage.
3. Listen for Clutch Noise: When trying to engage/disengage the clutch, listen for any unusual noises coming from the transmission area (grinding, squealing). This could indicate throwout bearing issues.
4. Test for Clutch Drag: With the engine off, try shifting into gear. If the engine is difficult to turn over (requires significant force), it points to a problem with clutch disc and/or pressure plate engagement.
5. Professional Inspection: Given the vehicle's mileage and the persistence of the problem after replacing critical components, a professional mechanic should inspect the clutch assembly. This involves removing the transmission to fully assess the clutch components. This is the most certain way to diagnose the problem.
In short, the issue is almost certainly within the clutch itself, not in the hydraulic system that you've already addressed. A mechanic with experience in clutch repair will be able to diagnose the precise problem. Ignoring the issue could lead to further transmission damage.
