Abstract: A combination lock of the type having peripherally gated tumbler wheels rotating about a common axis and adjusted by a rotatable dial and driving cam assembled on a spindle and supported for axial as well as rotary movement, the lock has an over-center spring coupled to a fence lever which normally holds the fence lever at a raised inactive position and has a fence lever accelerator which includes an anvil surface portion and a hammer portion supported by a spring formation which is stressed to an energy storage position responsive to rotation of the driving cam so that the hammer portion can be released from that position to impact against the anvil surface and impel the fence lever toward the driving cam to cause the fence lever to shift to a lowered coupled condition with the driving cam if the tumbler wheels are properly aligned and to cause it to be spring returned to the raised inactive position if they are not properly aligned.