This post covers a pull to one side when applying the brakes. Please see this post if you are experiencing a pull to one side when driving at a steady speed.
All modern braking system work by creating friction between brake pads and/or shoes and a metal surface, either a drum (drum brakes) or a rotor (disc brakes). Some vehicles use a combination of disc and drum brakes, and others use only disc brakes. When a combination of braking systems is used, the front brakes are always disc brakes. The clamping force that creates this friction is applied by a hydraulic system that starts with the application of the brake pedal and ends at the wheel assembly.
If your vehicle pulls to one side when you apply the brakes it typically means that you have a braking imbalance at one of the front wheels. Braking imbalances at the rear wheels do not typically cause a vehicle to pull because they do not directly effect the vehicle’s steering system. A common misconception is that one of the components in the braking system is applying more stopping force than any of the other three. The truth is that a braking component can never work better than it was designed to work. The real reason a vehicle pulls when braking is because one of the braking component is not working as well as it should. This causes the vehicle to pull to the side that has the proper working system.
If you have a pull when braking you should take your vehicle to a trustworthy repair shop and ask them to perform a “line-lock” test. If they don’t know what you’re talking about then take your vehicle to another shop. A “line-lock” test is the quickest way to determine which one of the four braking assemblies (one per tire/wheel) has a potential problem. It can also quickly eliminate the brake master cylinder from the equation. Many shops will simply start replacing braking component until the problem is solved without even trying to determine the cause. This almost always ends up costing you more money by paying for parts that were not bad in the first place.
I hope this was informative. If so, please leave a comment and let me know.