Texas CDL General Knowledge Practice Exam

If your brakes can get wet when driving through heavy rain, what can cause them to jackknife when brakes are applied?

1. Poor brake fluid quality

2. Trailer marbles

3. Trailer jackknife

4. Brake alignment

The correct answer is: Trailer jackknife

The correct answer relates to the scenario where wet brakes can lead to a jackknife situation. When driving a truck with a trailer, heavy rains can cause brake components to become wet, impacting their performance. If the braking force isn’t distributed evenly between the tractor and the trailer due to the loss of traction from wet brakes, it can result in a jackknife, which occurs when the trailer swings out and pivots toward the front of the vehicle. Understanding this, it's crucial to realize that while other choices may present potential issues, they do not directly address the specific impact that wet brakes have on the maneuverability of the trailer. For instance, poor brake fluid quality can affect overall braking performance but does not specifically lead to a jackknife situation caused by wet brakes. Similarly, terms like trailer marbles or brake alignment don't directly connect with the mechanics involved in how wet brakes might cause the instability leading to a jackknife effect.