Abstract: Bicycle seat post clamp mechanism comprising a locking shoe supported in a seat stay tube for movement to and from a locking position engaging the seat post. The locking shoe has a pair of beveled rear cam faces and a rear extension with a through hole. A pair of clamp members, each with a through hole and a beveled cam face, are supported in diametrically spaced circular openings in the wall of the seat stay tube, and extend along a horizontal axis transverse to the seat post. An adjusting screw extends through the clamp members. Tightening the screw draws the clamp members together causing the cam faces to move the locking shoe forwardly into its locking position against the seat post. The locking shoe and clamp members have circular cross-sections of a size small enough to be inserted through the openings in the seat stay tube and then to be assembled therein.