Toyota Repair: Trans wont go into reverse, automatic transmission fluid, differential unit

Question
I have a 1992 toyota corolla, 4A-FE with a A131 transaxle, the trans wont go into reverse suddenly, all other gears work fine (AUTO). I changed the trans oil and filter but the book says we need to add transaxle gear oil? Where is that going? I also check the linkage and looks fine, do you think i need a new trans?i just rebuilt completly the engine and runs like a baby but no reverse

Answer
The differential unit is seperate and requires gear oil, not automatic transmission fluid but that has nothing to do with it not going in reverse,if the fluid level is correct and the engine revs up but the car doesn't move in reverse then I would suspect a major transmission problem.