atebit, this is thread on the RC18 series but we will still help u out. You are talking about the revo right? Remove the screws that are holding the tranmission to the chassis, then take out the screws that go around the center of the tranny. Pull the two halves apart very slowly and gently making sure that none of the gears fall out. Look at all your gears and see if any of them have lost any teeth. Clean all the gears of debris and change the part. Then you can put it back together.
