During normal operations, when the brake pedal is pressed, the car will slow down. However, there may be times when pressing the brake pedal also results in a pull to one side or the other – this is an example of uneven brake pressure. There are many potential causes here.
How this system works:
In a normally operating brake system, the calipers will squeeze the rotors (discs) evenly on both sides of the car (or on all four corners in the case that you have four-wheel disc brakes). Pressurized fluid is sent to each caliper from the master cylinder in even amounts, and the force applied by each caliper is nearly identical.
This allows the car to slow down evenly, without any changes in direction. It also ensures even brake pad wear. However, in some instances, this does not happen. There are several possible reasons for uneven brake pressure, and not all of them have to do with the braking system.
Common reasons for this to happen:
- Stuck Caliper: The most obvious reason for brake pressure to be uneven is a stuck caliper. If the caliper is not free to slide back and forth on the slide pins, it will not engage the pad correctly. In fact, it might never completely disengage from the pad, creating a constant drag that can be noticed even when the brakes are not being used.
- Damaged Brake Line – Sometimes, brake line damage isn’t visible. If the inner liner of the line has been damaged, it can act like a restrictor, blocking the flow of fluid to the caliper and reducing braking force.
- Stuck Piston: The piston in the caliper needs to move back and forth freely, but if part of the seal has become wedged between the body of the piston and the caliper, it will not move as needed. This can also create uneven brake pressure.
- Bad Proportioning Valve: The proportioning valve is located under the hood and is responsible for adjusting the fluid pressure sent to the rear brakes. If the valve begins to fail, uneven brake pressure can result.
- Pad Contamination: Another possible cause of brake pull (uneven pressure) is if fluid has contaminated the brake pad. This can be brake fluid, grease or even oil.
- Using Two Different Types of Pads: If you have replaced the pads on one side the car but not the other (which is never recommended), there’s a chance you’re using two different types of pads. Different manufacturers use varying pad materials with very different performance characteristics.
- Uneven Tire Pressure: Uneven tire pressure can result in uneven brake pressure. Check your tires to ensure that they are properly inflated – this can be an inexpensive, hassle-free fix in some situations.
How important is this service?
Uneven brake pressure can be a sign of a serious problem. A stuck caliper can cause serious damage to the pads and rotors, and your stopping ability is compromised, as well. A damaged brake line will eventually fail completely. Pad contamination may be a sign of a brake fluid leak, an oil leak, or possibly a damaged CV boot if grease is the contaminant. A stuck piston can also be a very serious problem that can cost a lot of money if not caught in time.