Went on a weekend run (Destin to Orange Beach) got back and was flushing the boat with hatch up and heard a knocking, very consistent, three knocks then quiet...three knocks then quiet... I am pretty positive it is not the engine but the drive. Is it the bearing, U-joints, teeth missing?? How hard is this to tackle "Do it yourself"? Cost?

Thanks for the help.

Ok Walked outside after reading some post and turned the prop. Turns free, no problem no knocking. While the engine is running and not in gear it is knocking in the very back and I am almost positive it's something with the drive....Suggestions?

pull the drive off and check the U joint

New to all this, but if I can spin the prop fine does that narrow it down to the U-joint? What else should I look for when I pull the drive? Just trying to be prepared to inspect it all and know what to look for when I get it off. Thanks for the info on the U-joint.

Was the drive trimmed all the way up???? It needs to be down to prevent U joints from binding.

Also, it could just be the internal exhaust flappers.

Pull the upper magnet, if you find metal flakes or chunks, then look inside. If not, then it might be ujoints, but not likely. I say missing teeth on the gears. The most likely cause for knocking.
If you want to look inside, drain some oil down and pull the back and then the top cap. You should be able to see the gear teeth and any damage by then.
If you find metal on the magnet (not just fuzz) then pull the back cap. IF no metal then pull the drive and rotate the input shaft and inspect the ujoints.

Hope this helps.
Dick

The drive trimmed down almost all the way, as close as I could get it before hitting the concrete.

The boat was in neutral while I heard the knocking, and It was really easy to spin the prop with the engine off. I will look for metal flakes or chunks, thanks for the ideas. I am hoping to have time to pull the drive off the first of next week.

As for it's the exhaust flapper, I have heard that before and this is totally different sound, but I will do the easy check on that just to be sure.

I just Love fall, summer is over and you find out what needs to be repaced before next summer.

You need to put the drive in gear, with the engine OFF spin the prop back and forth. If you feel slop than it's the u-joints. The input shaft doesn't spin unless the motor is spinning.

I did not think about doing that before pulling the drive, thanks for the idea.

pulled the top cap on the drive, and had metal shavings. Who can tell me how much this is going to cost? Would I be better off trying to find a completely refurbed one?

Thanks for the help.

If anyone knows a good Drive guy around my area let me know. Located 1hr North of Panama City Beach and 2 hrs from Destin.