A surgical instrument includes a body, an ultrasonic blade, a clamp arm assembly, and a detent assembly. The clamp arm assembly includes a clamp arm pivotably coupled with the body at a pivot assembly. The clamp arm is operable to compress tissue against the ultrasonic blade. The detent assembly is configured to provide tactile resistance to pivotal movement of the clamp arm relative to the body beyond a predefined pivot angle. The detent assembly is configured to permit pivotal movement of the clamp arm relative to the body beyond a predefined pivot angle upon application of a force sufficient to overcome the tactile resistance