What Is Brake Lockup and How to Fix It
While automobile brakes are meant to stop a car, sometimes they can do their job a little too well. Thanks to hydraulic pressure and power brake booster muscle, it is quite possible to completely stop a wheel from turning while the vehicle is still in motion. When this happens, it is called brake lockup and it is not a welcome situation. Let’s look at what causes brakes to lock up and how to fix the problem.
What Does Brakes Locking Up Mean?
Brake lockup happens when the grip of the brake friction material overcomes the grip of the tire on the road. It can happen on dry pavement during a panic stop or on an icy road with just a touch of the brake pedal. Power brakes make it easier to lock up due to reduced pedal effort, but it can happen with manual brakes as well. It can also mean a situation where the brake mechanism fails to release its grip on the wheel, such as a stuck trailer brake.
Why Is Brake Lockup Bad?
A wheel that isn’t turning also isn’t controlling the travel direction of the vehicle. If this happens to a front wheel, it can no longer steer the vehicle.
Brake lockup can also damage your tires. If the vehicle is still moving while the tire is locked up, the road will cause a flat spot on the tire where the tread is worn down far more than the rest of the tire. This can throw off the tire balance, as well as cause erratic handling.
What Causes Brakes to Lock Up?
Let’s take a look at a few common causes of brake lockup.
Sticking Brake Caliper or Wheel Cylinder
If a brake caliper or wheel cylinder isn’t retracting correctly after brake pressure is let off, then it can stick in place. This causes the brake pad or brake shoes to hold in place against the drum or rotor. Corrosion around the brake caliper or wheel cylinder pistons can prevent them from moving freely. Damage to the piston bores can also cause the pistons to stick in their travel. The solution is to rebuild or replace the brake caliper or wheel cylinder.
If your car brakes locked up and now won’t move, you probably have severe rust affecting the braking components. Drum brakes can’t retract the shoes if all the parts are unable to move freely. This is less likely to happen with disc brakes, but in severe circumstances a brake rotor can rust badly enough to prevent it from passing through the brake pads. This is rare and usually only happens to vehicles that were parked for an excessive amount of time.
Non-Functioning ABS Unit
Almost every modern vehicle is equipped with an anti-lock brake system from the factory. So, what do anti-lock brakes do? Simply put, they prevent the wheels from locking up during braking. The anti-lock brakes unit is usually connected to the brake master cylinder. The ABS unit is a complicated component made up of a pump, valves and a control module. If any of these components malfunction, the overall unit will not operate correctly.
A problem with the anti-locking brake system unit will almost always trigger the anti-lock brake system warning light on the dashboard. If the ABS light comes on, understand that your anti-lock brakes are probably no longer working and need checked immediately. You should never ignore an ABS problem.
This seems obvious, but too many drivers ignore their tires as long as they are holding air. Take the time to check your tire tread depth on all four wheels. If the tread depth on a tire is less than 2/32”, the tire is worn out and needs replaced. A bald tire can’t grip a wet or icy road, making brake lockup a likely possibility.
Tires also wear out due to age. Check the tire date code on the sidewall. If the tire is more than six years old, it is no longer able to perform at its peak. Rubber gets hard and cracks as it ages, which reduces its ability to grip the roads and thus in turn can lock up your brakes.
How to Stop Brake Lockup
The key to preventing your brakes locking up when driving is good maintenance. There’s more to maintaining your brake system than just replacing worn brake pads and shoes. Each braking assembly needs inspected on a routine basis along with getting cleaned and lubricated where necessary. Tires need inspected and replaced as necessary. Ask your local NAPA Auto Care for a brake inspection to make sure your vehicle is in top braking shape.
A Brake Lockup Exception
There is actually one scenario where brake locking is done on purpose. For those who drag race, there is a point where it is necessary to spin the drive tires while holding the entire vehicle in place. This is done using a brake line lock kit that allows for one pair of wheels to stop. The driver steps hard on the brakes, activating the line lock to hold brake pressure on the desired wheels, then lets off the brake pedal to allow the driven wheel to turn for a burnout. Once the burnout is over, the brake locks are deactivated and the brakes work as normal.
Check out all the brake system products available on NAPAonline or trust one of our 17,000 NAPA Auto Care locations for routine maintenance and repairs. For more information on figuring out why your car brakes locked up, chat with a knowledgeable expert at your local NAPA Auto Parts store.
Photo courtesy of Flickr.
Brian Medford View All
With an automotive writing career spanning over two decades, Brian has a passion for sharing the automotive lifestyle. An avid DIYer he can usually be found working on one of his many project cars. His current collection includes a 1969 Olds Delta 88 convertible and a slant-6 powered 1975 Plymouth Duster.
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