What is the Johnson bar?
Answers
A hand valve that works the trailer brakes
A valve that indicates the fuel level
A valve that measures the amount of liquid in the air brake system
A valve that allows for the release of excess pressure in the braking system
The Correct Answer and Explanation is :
The correct answer is: A hand valve that works the trailer brakes.
The Johnson bar is a manual control lever used in older trucks and buses, primarily for controlling the trailer brakes. It operates as a hand valve that allows the driver to apply or release the brakes on the trailer independently of the vehicle’s main braking system.
Explanation:
The Johnson bar is often found in vehicles with air brake systems, especially in older or specialized vehicles like buses and semi-trucks. It provides an additional layer of control for the driver to engage or disengage the trailer’s brakes without affecting the vehicle’s own braking system. This is particularly useful when driving with a trailer, where the driver needs to manage the braking of both the vehicle and the trailer.
In most air brake systems, the trailer brake is controlled by a separate air valve that works in conjunction with the main brake pedal. However, the Johnson bar allows the driver to control the trailer’s brakes independently. The bar is usually mounted on the side of the driver’s seat or the dashboard and is operated by hand. When the bar is pulled or pushed, it sends air pressure to the trailer’s brake system, either applying or releasing the brakes.
This feature is especially useful in scenarios where the driver needs to manage the braking of the trailer when backing up, slowing down, or stopping. For example, in a semi-truck, the driver can use the Johnson bar to apply the trailer brakes while keeping the vehicle’s main brakes light, preventing the trailer from pushing the truck or making it unstable during maneuvering.
The Johnson bar is an important safety and operational feature, providing the driver with greater control over the vehicle-trailer combination, particularly in low-speed or complex driving situations. Modern vehicles may use electronic systems to manage trailer braking, but the Johnson bar remains a staple in older vehicle designs.