What do glad hands connect in a truck?

Glad hands are specialized connectors found in heavy-duty trucks that are used to connect the service and emergency air lines between the truck and the trailer. These connections are crucial for providing air to operate the trailer’s brakes, which include both service brakes and emergency brakes. By using glad hands, truck operators can ensure a secure and reliable connection for air supply, which is essential for safe vehicle operation.

This connection allows the brake system to function effectively by enabling the transfer of compressed air from the truck to the trailer, activating the brakes as needed. The design of glad hands makes it easy to connect and disconnect air lines, simplifying the coupling process during loading and unloading.

Other options, while related to vehicle operations, do not pertain to the specific use of glad hands. For example, fuel lines and transmission fluids are unrelated to the air brake system and would use different types of connections. Brake systems, while involved in the overall braking function, are not what is specifically connected by glad hands. Thus, the correct answer accurately highlights the role of glad hands in connecting service and emergency air lines in a truck setup.