Semi truck brake fluid is a non-toxic, organic liquid thatâs colorless and odorless. You might start noticing brake fluid leaks if your truck has a gurgling sound, when it seems like the brakes arenât working, or if the pedal starts feeling squishy. Brake fluid leaks are dangerous because they reduce the effectiveness of the vehicle’s brakes. To fix this type of oil leak, first consult your owner’s manual for instructions on how to find and remove the source of leakage. For example, it might be as simple as topping off your brake fluid reservoir or tightening loose connections in hoses or joints. If you still notice a leak after inspecting these areas you may need new braking system parts such as brake lines or seals for calipers.