Radiological detection resistant combination lock

A combination lock of the type adapted for changing of the combination by a change key, comprising a lock case having front and rear walls and a cylindrical tumbler post normally extending along a horizontal axis rearwardly from said front wall, a tumbler wheel stack formed of a plurality of tumbler wheels loosely journaled on the tumbler post for rotation about the axis thereof and each including an annular outer rim portion and an inner annular hub portion having formations about its periphery releasably intercoupling the hub portion and rim portion at any of a plurality of relative angular positions, a peripherily gated rotatable driving cam driven by a rotatable dial, means for driving the tumbler wheels responsive to rotation of the dial and driving cam a fence lever pivotally connected to a bolt for shifting the bolt between locked and unlocked positions, the rim portions of said tumbler wheels having peripheral gates therein to receive therein confronting portions of a fence on said fence lever when the tumbler wheels are properly aligned following dialing of the proper lock opening combination, said rear wall of the lock case having an opening therein for insertion of a combination change key into the lock case and rotation thereof at as position located radially outwardly of the tumbler wheels adjacent the outer peripheries thereof, means supporting said tumbler post within the tumbler wheel hub portions for nonrotatable axial movement between first and second positions and having shoulder means forwardly and rearwardly abutting the wheel hub portions of the tumbler wheel stack for movement of the hub portions axially relative to said outer rim portions between coupled and decoupled relation therewith, rim restraint means restraining said outer rim portions against axial movement, and tumbler post positioning means within the lock case activated by rotation of the change key within the lock case between coupled and decoupled positions for axially moving the tumbler post and said tumbler wheel hub portions to shift the tumbler wheel hub portions to decoupled relation with the tumbler wheel rim portions for combination change by rotation of the hub portions to new combination positions relative to their rim portions responsive to rotation of the dial and driving cam to a new changed lock opening combination, and said tumbler post positioning means being operative to return the tumbler post and the tumbler wheel hub portions axially to positions again intercoupling the tumbler wheel hub portions and their respective rim portions responsive to rotation of the change key to coupled position.