jermainezey

please i have a nitro stampede that i got as a roller i have snice build the whole truck i have a used traxxas .15 engine on i put on a brand new spar gear last night and i put a smaller white one on today but it does the same thing every time i start the engine and try to rev it a lil bit the truck acts as it going go but then it kees happen the gear grinds away and the truck once again still have gone any where what could be wrong with it am starting to give up on it