1. Master Cylinder:
* Fluid Level: Check the master cylinder reservoir. Is it full? If it's low or empty, you have a leak somewhere in the system. Top it off with the correct DOT 3 brake fluid (never use DOT 4 or 5.1 with a system designed for DOT 3).
* Master Cylinder Failure: A faulty master cylinder can't build pressure. You might need to bench bleed it or replace it entirely. A visual inspection for leaks is crucial.
* Master Cylinder Pushrod Adjustment: Ensure the pushrod extending from the pedal is correctly adjusted to the master cylinder. Too much or too little travel can prevent proper pressure build-up. This usually requires adjustment at the pedal itself.
2. Slave Cylinder:
* Fluid Leak: Check for leaks around the slave cylinder (located on the transmission). Even a tiny leak will prevent pressure build-up. This often manifests as fluid dripping onto the transmission or bell housing.
* Slave Cylinder Failure: The slave cylinder might be faulty, preventing it from pushing the clutch fork. It might be internally leaking or seized. This usually requires replacement.
* Slave Cylinder Rod: Check that the slave cylinder's pushrod is properly seated and that it moves freely. Sometimes it can get bent or damaged during installation.
3. Lines and Hoses:
* Leaks: Carefully inspect all hydraulic lines and hoses connecting the master and slave cylinders for leaks. Look for wet spots, bulging, or cracks. Replace any damaged components.
* Clogged Lines: Though less common, a severely clogged line can prevent fluid flow. This is rare, but if you suspect it, you may need to flush the system.
4. Air in the System:
* Bleeding the Clutch Hydraulics: Air in the lines is the most likely culprit. You *must* bleed the clutch system thoroughly. This is a two-person job. One person pumps the clutch pedal slowly and steadily, the other opens and closes the bleeder valve on the slave cylinder. This process needs to be done several times until no more air bubbles are seen and a firm pedal is achieved. There are various bleeding methods – consult a repair manual for your specific truck.
5. Clutch Installation:
* Incorrect Installation: While less likely if you had a professional perform the replacement, a mistake during the clutch installation itself (e.g., incorrect alignment, damaged parts) could prevent the clutch from disengaging, indirectly affecting pedal feel. This would manifest as difficulty shifting, not necessarily no pedal pressure. However, if the clutch fork is bent or misaligned, this could cause an indirect pressure issue.
Troubleshooting Steps:
1. Start with the easiest: Check the fluid level and look for obvious leaks.
2. Bleed the system: This is the most likely fix.
3. Check the master and slave cylinders: Inspect for leaks and damage.
4. Inspect lines and hoses: Look for cracks or leaks.
5. Consult a repair manual: A factory service manual for your 1991 Chevy Cheyenne 454 will provide detailed diagrams and instructions.
Warning: Working on hydraulic systems requires care. Brake fluid is corrosive. Wear safety glasses and gloves. If you are uncomfortable working on your vehicle's hydraulic system, take it to a qualified mechanic. A faulty clutch can lead to serious accidents.
