when you select reverse make sure you are completely stopped and not rolling backwards, also make sure your car is on idle, if you still have problems selecting reverse i.e. crunching then you have probably chipped reverse gear, and your other gear problems have you checked your gearbox oil level? drain the oil and use a magnet to see if there is any shrapnel in there! or you have just worn your clutch fully out and the smell is because the clutch is fighting to keep friction! hope this rambling helps!