1. Bleeding the System: This is the MOST likely culprit. Air in the hydraulic system will prevent the clutch from engaging properly. You need to bleed the system thoroughly. This is a two-person job, ideally.
* Proper Bleeding Procedure: Use a clear hose attached to the bleeder valve on the slave cylinder. Have someone slowly pump the clutch pedal while you monitor the fluid for bubbles in the hose and open/close the bleeder screw. Repeat until no more air bubbles appear. There are various methods (gravity bleed, pressure bleed) but a standard two-person bleed is generally sufficient.
2. Incorrect Installation:
* Slave Cylinder: Was the slave cylinder installed correctly? Was it fully seated and properly aligned? A misaligned slave cylinder won't push the throwout bearing correctly.
* Master Cylinder: Did you properly install the master cylinder pushrod? It needs to be adjusted correctly to engage the slave cylinder properly. A common mistake is improper pushrod length or misalignment.
3. Other Hydraulic System Issues:
* Leaking Lines: Check all the hydraulic lines for leaks. Even a small leak can prevent the system from building up sufficient pressure.
* Damaged Hose: A collapsed or kinked hose will impede fluid flow.
* Low Fluid: Make sure the master cylinder reservoir is full of the correct DOT 3 brake fluid (or equivalent specified for your vehicle).
4. Clutch Problems (Outside the Hydraulic System):
* Clutch Disc/Pressure Plate: If the clutch disc is worn out, damaged, or improperly installed, it might not engage even with sufficient hydraulic pressure. This is less likely if the clutch was working before the cylinder replacement, but it's a possibility.
* Throwout Bearing: A worn or damaged throwout bearing could prevent the clutch from disengaging properly. This usually manifests as difficulty shifting, not necessarily a complete failure to engage.
* Transmission Issues: Although less probable, there could be an issue inside the transmission itself preventing engagement. This is less likely than the hydraulic or clutch problems.
5. Air in the System (Again): Even after bleeding, a small amount of air can remain. It's sometimes helpful to bleed the system multiple times. Consider a pressure bleeder for a more thorough job.
Troubleshooting Steps:
1. Visually inspect: Carefully examine all components for leaks, damage, or misalignment.
2. Bleed the system: This is the most important step. Do it meticulously.
3. Check fluid level: Ensure the master cylinder reservoir is full.
4. Check for leaks: Look for fluid dripping anywhere along the lines.
5. Re-check installation: Ensure all components are correctly installed and seated.
6. If still not working: Seek professional help from a mechanic specializing in clutches and transmissions. They have tools and expertise to diagnose more complex issues.
Remember safety: Always work in a well-ventilated area when working with brake fluid, as it is toxic and can damage paint. Wear gloves to protect your hands.
