Why would your brakes pedal get really hard and the brakes lock up after driving 4 miles?

Answer 1

Happened to me once when I changed exhaust in my car- hot exhaust near brake line expanded fluid, locked up brakes. Another thing comes to mind, drum brake master cylinder on disc brake car, did you replace master cylinder before having problem? Any time a brake friction component comes into contact with a braking surface, heat is generated. If the shoe or pad generating that heat is not removed from contact with the drum or rotor for an adequate period of time between applications, heat is built up to an excessive level. This creates both a glaze upon the contact surfaces and a boiling condition of the fluid within the brake cylinder or caliper. This boiling increases the pressure exerted upon the braking surfaces further, leading to brake lockup; and, should the brakes be applied, the glazing which has occurred prevents normal friction action from slowing the vehicle as intended. This condition results in more pressure being applied to the service brake pedal in an effort to control the vehicle, which creates yet more heat, and more pressure inside the system. What is felt at the brake pedal is increased resistance due to these factors. This is the 'hard pedal' associated with the condition of 'brake fade'. If a caliper is sticking on its slides, or a brake shoe is adjusted too tightly, the result will be as depicted above. In addition; should the master cylinder be overfilled, not allowing for the expansion of the brake fluid when hot, this can occur. Brake fluid which has absorbed an excess of water will also cause this, due to the lowering of its boiling point by that water; and, since it is hygroscopic, brake fluid can absorb as much as 3% water by volume in a sealed plastic sales bottle in a year's time just through the pores in the plastic. Taken together, these things make it all too clear what can happen when brake systems are left without maintenance monitoring; and, if your car is "right", the car of the guy coming toward you may be faulty in this regard. Be safe; keep a professional eye on the brakes: A short-cut here is a short-cut nobody should take...