Reverse is not synchronized on the Santa Fe (or any other vehicle I know of). If yours won't go into reverse, move the shifter to neutral, let out the clutch enough that it will start to engage, and depress the clutch again before shifting into reverse. This works every time on my manual Santa Fe. It's a trick that every driver used to know but, with the decline in popularity of manual transmissions in the US, it seems to have been largely forgotten. Hope this helps!