1971 mercury 500 drive shaft questions

[Jdgdtt]

I have a 1971(as best as i can tell) mercury 500 that I have wasted the gears and drive shaft on. I pulled the shaft and im trying to find a replacement. The issue is that I have an extension kit and I cant find the correct drive shaft. Mine measures 17” from the base of the lower unit to the top of the shaft. Seems 15” and 20” are standard. Anyone have any knowldge on this subject? Worried it was part of the kit and I’m in trouble.

 

[Chinewalker]

The "standards" are ballpark/minimum numbers. If you're adding the 5-inch extension to your motor, you need a driveshaft that is exactly 5-inches longer. Go to one of the parts sites and look up the correct driveshaft part number. You may also find a newer shaft that will work - and gain you stainless steel at the seal areas, as the 1971 shafts were still prone to rusting.

 

[racerone]

A " long shaft " motor is for a 20" transom !-----Not to be confused with the measured length of the driveshaft.---And at 17" I believe your transom is 15" high and the motor is a " short shaft " motor

 

[Jdgdtt]

Thanks for the information. Is it at all odd to have a short shaft motor with and extension kit? My motor has a 5” extension on it.

 

[Jdgdtt]

So I took some measurements and the transom is 20”, the mid section is 15” with a 5” extension. The drive shaft measures 25” over all. I believe that is a short shaft. Is there extension at the top of the drive shaft? Any help is appreciated. Not ready to separate the mid section if I dont have to.