A drivetrain assembly includes a transmission and a driveshaft that are joined together by a transmission flange and a driveshaft flange that has a plurality of pre-assembled bolts. The driveshaft flange defines a plurality of holes and countersink recesses and the bolts are secured to the driveshaft flange by a bolt retainer disposed in each of the countersink recesses between the transmission flange and the driveshaft flange. A method is disclosed for assembling a transmission flange and a driveshaft flange that defines a plurality of holes and countersink recesses. A bolt is assembled into each of the holes and countersink recesses and a bolt retainer is attached to each of the bolts and nested inside the countersink recesses to retain the bolts on the driveshaft flange. The bolts on the driveshaft flange are then installed into the threaded holes of the transmission flange.