* Internal Leaks in the Brake System: This is a very common cause. A leak in a wheel cylinder, caliper, or even a brake line can allow brake fluid to slowly seep past the piston seals. This causes the piston to slowly extend, applying the brakes even when you aren't pressing the pedal. You'll likely see brake fluid leaks around the affected area (wheels, calipers).
* Sticking Calipers or Wheel Cylinders: The pistons in these components might seize or become sticky due to corrosion, rust, or a build-up of debris. This prevents them from fully retracting, leading to constant, slight brake application.
* Master Cylinder Issues: Although less likely to cause *slow* lock-up, a failing master cylinder can sometimes lead to gradual brake application. A leaking or internally damaged master cylinder may not return fluid properly to its reservoir.
* Proportioning Valve Problems: The proportioning valve regulates brake pressure between the front and rear wheels. If it malfunctions, it could send too much pressure to the rear brakes, causing slow lock-up. This is less common than caliper or wheel cylinder issues.
* Parking Brake Cable Issues: A partially engaged parking brake cable can cause slow brake application. Make sure the parking brake is fully disengaged.
* Low Brake Fluid: Although less likely to cause a *slow* lock-up, extremely low brake fluid can lead to air in the lines, and air doesn't compress as well as fluid, leading to uneven and potentially dangerous braking.
What to do:
1. Do NOT drive the vehicle until the problem is fixed. Driving with slowly locking brakes is extremely dangerous.
2. Inspect the brake system for leaks. Look carefully around all four wheels, brake lines, and the master cylinder for any signs of brake fluid leaks.
3. Check the parking brake. Make absolutely sure it's fully released.
4. Check your brake fluid level. It should be within the "MIN" and "MAX" markings on the reservoir. Low fluid is a *symptom*, not the root cause, but needs to be addressed.
5. Have a mechanic inspect your brake system. This is the safest course of action. They have the tools and expertise to diagnose and repair the problem correctly. Ignoring this issue can lead to brake failure and an accident.
This is not an exhaustive list, but it covers the most probable causes. Professional diagnosis is strongly recommended.
