Abstract: A down hole drilling motor shaft security apparatus is disclosed. The apparatus has a general body housing threadedly attached to a lower radial bearing housing and an output shaft extending from the lower radial bearing housing. Within the general body housing is a thrust bearing assembly that secures a portion of the output shaft within the general body housing and the lower radial bearing housing. An intermediate sleeve having a capture groove of an elongated predetermined width is threadedly attached to the output shaft. An interference structure that is secured to the general housing extends radially into the capture groove in a manner that prevents axial loads from being transmitted to the intermediate sleeve from the interference structure while the bearing assembly is intact.

Abstract: An interference structure is provided in a drilling motor to engage the motor drive shaft assembly if the thrust bearings fail and the drive shaft moves axially a preselected amount. The interference structure is protected from wear common to drilling motor use. The structure assures the recovery of all drilling motor parts if all thrust bearings fail.

Abstract: A flexible drilling motor drive shaft coupling has two torque transmitting portions spaced apart axially, preferably, by a compression unit that is secured to one portion by a tension link and entrapped within the other portion. The tension link is, preferably, a cap screw extending along the axis of rotation of the coupling.