74 Searay 302 5.0L 225 HP Mercruiser. How do you know if the lower or the upper unit has gone out. I know one of the two have or maybe both. Lower unit shouldn't even engage if put in gear right? Started it up, put it in forward engine dies. Start it up, put in reverse nothing engages and rpm's go up. Please help or advice. From Chain Of Lakes Area in Illiniois, if anyone knows mechanics or a side job.