The mini v brakes had the same problem from the start. Back then I managed to get the front brake to function somewhat. I could never get the rear brake to work, so I deattached it and rid the bike without it for two years. Later the hole that the adjusting screws on the brake go into, stopped holding the screws so I had no choce but to replace the brakes. Allthough they are "mini", the new v-brakes are the same size as the old.

Also shifting with the front derailleurs was faulted from the get go. It required abnormal pressure on the shifter and consequently made alot of noice to change from the larger chain ring to the smaller. I coudn't bother. Again, I deattached it as I coudn't, nor had I the need to use them for two years.