Dead clutch bearings... common nitro problem. but do NOT continue running with bearings filled with wd-40.. the clutch will start slipping because the oil from the inside of the bearing will fly out to the clutch shoes. And to prevent later problems, buy new clutch bearings such as the one from www.avidrc.com they are $1 a piece, so buy like 10-15 and it should solve your problem for the rest of your nitros life