Question If you don't pull a dolly out from beneath the rear trailer before unlocking the pintle hook: Answers The tow bar may fly up. The kingpin may break. The brakes may become unlocked. Explanation Never unlock the pintle hook with the dolly still under the rear trailer. This could cause the dolly tow bar to fly up, possibly causing serious injury. Take a FREE Practice Test Now This questions appears in the following tests: Washington Double ,