Problems with drive shaft out of 1977 mercury 70 hp Thunderbolt 700 series

Dennis1979

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Mar 7, 2013
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I recently bought a 1977 mercury 70 hp. Had it on the water several times with no problems. The last time I had the motor on the water (w/ aluminum V bottom fishing boat) I had several people in the boat and the water was rough that day. I plained out running about 25- 30 according to the GPS, the boat stopped with a sudden rev of the motor like I spun a hub. After taking it to shop it was confirmed that the drive shaft was wore out at the splins. My question is I am replacing the drive shaft, should I be worried about the splines in the motor or the crank. If I replace the drive shaft will I continue to have problems with spinning the shaft out?
 

Laddies

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Sep 10, 2004
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Re: Problems with drive shaft out of 1977 mercury 70 hp Thunderbolt 700 series

The crankshft spline should be inspected very carefully and the driveshift fit needs to be checked before it is installed in the lower unit the splines were damaged because of lack of grease when the unit was reinstalled and corrosion over the years.
 
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