Why Would the Rear Brakes Randomly Lock Up?

Brake Brake System Brake Disc Caliper Front Brake

I answer a lot of questions on Quora. Many of those questions are about automotive things that may be of interest to CarNewsCafe readers. Like this one.

Why would the rear brakes of a Forward Wheel Drive car randomly lock up?

My Answer: Unlike the front brakes on a car, the rear brakes on most vehicles made to pass North American and European safety requirements will have a “parking brake” that only engages the rear wheels. This brake is usually physically separate from the pedal-actuated system and is most often mechanical, utilizing springs to force either brake fluid into a caliper or pads up against the rotor/drum surface. If anything in that mechanical portion fails, the brakes can “lock up.”

Other issues on modern cars can also cause (usually brief) brake lockup on the rear wheels. Failure of the electronic parking brake control, for example, might cause the rear brakes to engage and remain so.

With most more modern cars, a likely culprit will be a clogged/disconnected brake limiting valve (BLV or, sometimes, brake pressure reducing valve/PRV). This is used to vary the pressure to the rear wheels to allow for braking in various conditions in which the rear wheels may need more or less pressure to compensate for vehicle movement or control as part of the stability and body roll control systems.

Aaron Turpen
An automotive enthusiast for most of his adult life, Aaron has worked in and around the industry in many ways. He is an accredited member of the Rocky Mountain Automotive Press (RMAP), the Midwest Automotive Media Association (MAMA), the Texas Auto Writers Association (TAWA), and freelances as a writer and journalist around the Web and in print. You can find his portfolio at AaronOnAutos.com.