i have a 77 mercruiser 120 or 140 not sure how to tell but outdrive says 120, anyway i replaced the impeller on the lower unit, now it is acting like it is stuck in gear. when i started it after replacing impeller the prop spun at a high speed and if i try to shift it into gear it stalls the motor. not sure if the motor would have stalled before i changed the impeller though. it was overheating so i started there and seems im about to b finished there. i hate paying a mechanic pls tell me i can fix this without taking it all apart again lol