No Reverse Gears

Fluid level, shift linkage or cable, low line pressure, pump inlet filter and seal assembly, manual valve (stuck or damaged), valve body leakage (gasket damage), improperly torqued valve body bolts, reinforcing plate bolts improperly torqued or loose, direct clutch assembly (only if 3rd gear is also inoperative), reverse clutch assembly, reverse planet assembly and reverse ring gear.