Hold down springs are designed to keep the brake shoe firmly against the backing plate. If the hold down springs are weak then the shoe could cock causing a binding condition. The replacement of rear shoe hardware should be suggested each time the rear brake shoes are replaced to prevent this from happening. The shoe lands keep the brake shoes square with the drum and provide a friction surface for the shoes to move against. Over time the bosses can become grooved and corroded as in Figure This grooving can allow the brake shoe to hang on either the apply or release of the brakes which can cause lockup.
The shoe lands should be checked during the inspection and if rear brake service is performed they should be cleaned and lubed. The shape of the backing plate mounting hole keeps the wheel cylinder from rotating.
As the backing plate and wheel cylinder rust this fit is affected which allows the wheel cylinder to rock as the brakes are applied. This rocking can be enough to cause the wheel to lockup during certain types of braking.
The typical fix when this occurs is to replace the wheel cylinder and backing plate. Always check these types of wheel cylinders for proper fit during the brake inspection. An out of round brake drum or drums that vary in diameter too much from side to side could cause a one wheel lockup condition Figure Measuring drum runout or out of roundness is not easy in the field. Current micrometers do not allow a repeatable measurement to be taken. Using the brake lathe and a dial indicator is only accurate if the lathe and adapters are in the proper condition.
If you suspect the rear brake drum is causing the problem install it on the other side of the vehicle and test drive the vehicle. If the problem moves to the opposite side then you are on the right track, if not continue your quest.
If an axle seal or wheel cylinder leaks and contaminates the brake shoe s it changes the coefficient of friction. If it is mild contamination then the friction is increased while severe contamination will cause a reduction in friction See Figure A common source of contamination occurs during the installation of new shoes.
An effective method of preventing this is to put wide masking tape on all the friction before starting the job. Once complete simply remove the tape and the shoes are perfect.
When brakes lock up, the vehicle may veer sharply to the left or right, and the back end may fishtail causing the driver to lose control [source: Car Talk ]. If this happens while you're driving, pump the brakes consistently until you come to a complete stop, and get the car to a mechanic as soon as possible. Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close. Mobile Newsletter chat dots. Mobile Newsletter chat avatar. Mobile Newsletter chat subscribe.
Brake Problems. If you slam on your brakes and they lock up, you could burn a lot of rubber. This can happen when you are both braking hard to avoid an accident, or braking gently to glide to a stop. Essentially, the force of applying the brakes even lightly can activate the full stopping-power of your brakes — bringing you to an abrupt and less-than-safe stop. You might even skid. When this happens, you can expect steering and control of your vehicle to be extremely difficult.
Our technicians will ask what wheel or wheels seem to be locking up and when. Any information you can provide will help with the diagnosis and repair. So, what actually causes brakes to lock up? This is the question that we will be answering in this section. Take a look at the list down below to find a brief explanation of this concept, and keep reading to get all of the details.
The main reasoning behind locked brakes lies in the amount of friction within them. When you use the braking system, there are two general points of contact that create friction between each other. The first one is inside of the braking system. This is where the individual components of the brakes will come in contact in order to slow down and stop the vehicle.
The second point of contact is between the actual tires and the road. When you are driving, the wheels on your car are gripping onto the ground, allowing you to stay in one place without turning or spinning around.
When there is too much friction in the brakes, usually due to the driver slamming on the pedal at fast speeds, the wheels will not have enough time to catch up. In other words, the friction inside of the braking system will be greater than the friction between the tires and the road. As a result, the tires will stop moving while the vehicle is still in motion, causing them to slide over the pavement.
During this event, the brakes will be locking up inside of the car.
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