* Brake System Leaks: A leak in the brake lines, wheel cylinders, or calipers can cause a loss of brake fluid pressure, leading to uneven braking and potential lock-up. Look for fluid leaks around these components.
* Seized Caliper(s): A caliper piston can seize, preventing it from retracting properly. This keeps the brake pads constantly pressed against the rotor, leading to dragging and lock-up. This is a very common cause.
* Master Cylinder Issues: A failing master cylinder can cause uneven brake pressure distribution, potentially leading to front brake lock-up.
* Vacuum Booster Problems: A malfunctioning vacuum booster reduces brake assist, requiring much more pedal effort. While this might not directly *cause* lock-up, it could contribute to the problem if the driver overcompensates.
* Proportioning Valve Problems: This valve regulates brake pressure between the front and rear brakes. A malfunction can cause too much pressure to the front. Less common but possible.
* ABS Issues (if equipped): While less likely to cause *complete* lock-up, a faulty Anti-lock Braking System (ABS) module or sensor could contribute to uneven braking and potentially make the problem worse.
* Brake Lines/Hoses: Restricted or damaged brake lines or hoses can also impact brake pressure and distribution.
* Low Brake Fluid: While unlikely to cause a *sudden* lock-up, extremely low brake fluid levels indicate a leak and a significant safety hazard.
What to do:
1. Do not drive the truck. This is crucial for safety.
2. Check the brake fluid level. Is it low? This points to a leak.
3. Inspect the brake system visually. Look for leaks around the calipers, wheel cylinders, brake lines, and hoses.
4. Check for dragging brakes. Try to turn each front wheel by hand. If a wheel is difficult to turn, that indicates a problem with that brake.
5. Have the vehicle inspected by a qualified mechanic. This is essential for accurate diagnosis and repair. A professional will have the tools and expertise to properly identify and fix the underlying issue.
Ignoring this problem is extremely dangerous. The consequences of locked brakes can be catastrophic. Get it fixed immediately.
