Master Cylinder:
* Low brake fluid: This is the simplest and most common cause. Check the fluid level in the master cylinder reservoir. If it's low, you need to find the leak and refill it *before* attempting to diagnose further. Low fluid doesn't *cause* the lack of pressure, but it's the symptom of a much bigger problem.
* Master cylinder failure: The master cylinder is the heart of the braking system. Internal seals can wear out, causing leaks or a loss of ability to build pressure. This often presents as a spongy brake pedal or no brakes at all. A rebuild or replacement is needed.
* Internal leakage in the master cylinder: Fluid could be leaking internally, bypassing the pistons and not building pressure.
Brake Booster:
* Vacuum leak: The booster uses engine vacuum to assist in braking. A leak in the vacuum line, a cracked booster diaphragm, or a faulty check valve will drastically reduce braking power.
* Booster failure: The booster itself can fail, rendering it ineffective.
Wheel Cylinders/Calipers:
* Wheel cylinder leaks (drum brakes): These are located at each wheel (on the rear in this case; most likely rear drum brakes). Leaking wheel cylinders allow fluid to escape, reducing brake pressure in the system. This is a common cause of brake fluid loss.
* Caliper leaks (disc brakes): If your C10 has front disc brakes, leaking calipers can cause the same problem as leaking wheel cylinders.
Proportioning Valve:
* Valve failure or blockage: The proportioning valve (if equipped) distributes brake pressure to the front and rear wheels appropriately. A malfunction can significantly reduce braking ability.
Brake Lines and Hoses:
* Leaks: Any leaks in the brake lines or hoses will cause a loss of pressure. Inspect all lines and hoses carefully for cracks, rust, or damage. Pay special attention to areas where the lines are bent or rub against other components.
* Clogged lines: Less common, but possible; a blockage in the brake lines prevents fluid from reaching the wheels.
Other Possibilities:
* ABS issues (if equipped): Some later-model C10s might have had optional anti-lock brakes. A malfunction in the ABS system could interfere with braking. This is less likely on an '83.
* Brake pedal assembly: A problem within the pedal assembly itself, though less likely, could affect pressure.
Troubleshooting Steps:
1. Check brake fluid level: This is the absolute first thing you should do.
2. Inspect brake lines and hoses: Look for leaks, rust, and damage.
3. Check the master cylinder: Look for leaks around the cylinder and assess the condition of the fluid.
4. Test the brake booster: Check the vacuum hose for leaks; this usually involves disconnecting the hose from the booster and checking for suction.
5. Check wheel cylinders/calipers: Inspect them for leaks and see if they are functioning correctly (this often requires removing the wheels).
Important Note: Brake failure is a serious safety issue. If you are unsure about any of these steps, it is best to have a qualified mechanic diagnose and repair the problem. Driving a vehicle with no brake pressure is extremely dangerous.
