Boat: 1999 Chaparral 1830 Sport<br />Motor: Merc 4.3 Litre V6 EFI<br />Drive: Mercruiser Alpha One / SN 1.81R OL478554<br /><br />I have a 1999 Mercruiser Alpha One drive w/ 120 hours and I have a problem. Last year I hit a dead head which ruined the prop and I took it into our dealer where I purchased the boat and after they inspected it they told me the prop shaft was slightly bent on the edge of tolerance and suggested replace it rather than leave it in because the vibration could cause problems long term. I decided to replace it rather than take any chances and everything seemed fine after the repair. All parts that I have every replaced are Mercury brand so I'm not using any goofy OEM parts or fluids.<br /><br />A couple days ago I took the boat out I noticed that when I suddenly reduced speed from high throttle to low throttle that there was a loud clunk sound from the drive. I stopped the boat and checked the prop and lower unit for damage because it sounded like I hit something but the everything was OK. Later in the day I tried going from high speed to low speed again and it made the exact same clunking sound. The boat does not vibrate and it doesn't make any noise unless I slow down abruptly from high speeds. As for fluids I checked everything and everything is topped off w/ no leaks. <br /><br />I was going to take it out today but after checking things out again I noticed that the prop shaft has 3/4" play when moved in and out which seems excessive to me. There is no play side to side just in and out. It seems logical that this could be causing the clunking sound when I abruptly reduce speed. I'm curious what the normal play is on a prop shaft when moved in and out for an Alpha One drive. If this isn't the problem what other problems would cause these symptoms.<br /><br />Thanks,<br /><br />Chris
