If the vehicle swings to one side when the brake pedal is depressed, what could be the cause?

When a vehicle swings to one side upon braking, it typically indicates an uneven distribution of braking force. In this scenario, the presence of wet brake lining can lead to reduced friction on the affected side, making it less effective in slowing the vehicle down compared to the opposite side. As a result, the vehicle shifts or swings toward the side with the better-braking performance.

Moisture on brake linings can cause them to become slippery, which directly affects the vehicle's stability and handling when brakes are applied. This situation is particularly dangerous as it can lead to loss of control or longer stopping distances. Thus, identifying and addressing wet brake linings is crucial for safe vehicle operation.

In contrast, other options present more unrelated issues. A bad rotor brush affects electrical components and is irrelevant to braking dynamics, faulty spark plugs are related to engine performance rather than braking, and worn suspension components might indirectly influence vehicle stability but wouldn't specifically cause uneven braking responses like wet brake linings would.