A threaded nipple (26) at the closed end of a linear hydraulic motor (12) is received within a recess (82) in a frame member (78). Single clamp members, or individual clamp members (88), have recesses (92) that receive lower portions of the nipples (26). Bolts (94) extend through the clamp members (88) and screw into threaded openings in the frame member (78). This clamps the nipples (26) between the frame member (78) and the removable clamp members (88). End members (22) at the rod ends of the cylinders (12) include keys (66) that are received within recesses (80) formed in another frame member (76). Bolts (76) extend through the end member (22) and screw into threaded openings (84) in the member (76). A mounting frame has transverse mounting frame members (74, 102, 74null, 102null) that are used for mounting the drive assembly in an installation. The mounting frame members (74null, 102null) may have end portions (208, 210, 212, 214, 240, 242) that serve as cells in a trailer installation. The drive units may have a continuous piston-rod (50null) or short piston-rods (50, 50null) that are attached to push-rods (14, 14null). The connection may allow a limited amount of pivotal movement between the push-rod (14null) and the piston-rod (50null).