I was speaking from experience on the Auto transmission only. I'm not sure if the manuals use the same overdrive unit as the automatics or not. In the automatic, the intermediate output shaft (from the three speed transmission) goes directly into the overdrive unit at the back of the tranny. If the overdrive is turned off, the intermediate output shaft is coupled directly to the final output shaft. If the overdrive is engaged, however, the intermediate output shaft drives the center of the overdrive unit, and via planetary gears and magic produces an additional ratio that is coupled to the final output shaft via the outside of the overdrive unit.

Now, due to the construction of the OD unit and an inherent ratchet type mechanism, if the overdrive is engaged AND the transmission is put in reverse, the intermediate output shaft is connected to the final output shaft, AND the overdrive is engaged. In other words, the direct coupling and the "multiplied" output of the overdrive unit are hitting the output shaft at the same time! End result is that the intermediate output shaft turns into a pretzel... just to rub salt in the wound!

If someone has OD info on this for a manual, please let me know.

John
1990 240DL B230F 2Kmiles