reverse went out

I have a mazda b series truck and the reverse just went out in it. When i put it in reverse nothing happens accept there is a little hum noise coming from what i think is the tranny. Does anyone know what this problem is? Reverse anchor?

with not knowing the year of your truck I would say it would be your high gear clutch. I had a Monte Carlo were 3rd gear started to go out then reverse.. it was cheaper to replace the tranny than it was to fix the broken one. Hope this helps.. either way.. plan on spending a lot of money