No Reverse Engagement, Forward Okay

Check fluid level, drive axles, external and internal shift linkage, low line pressure, valve body (improperly torqued bolts, gasket damaged or off location, oil pump shaft broken, forward clutch valve, manual control valve, main regulator valve and springs), oil pump assembly damaged components, support assembly (driven sprocket), forward clutch assembly, reverse clutch assembly, one-way clutch assembly (planetary) and output shaft splines damaged.