1965 GTO Conversion To Manual - Flywheel Hole Size - Pontiac GTO Forum
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post #1 of 3 (permalink) Old 02-16-2013, 05:34 PM Thread Starter
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1965 GTO Conversion To Manual - Flywheel Hole Size

I'm in the process of ordering parts for my conversion to a manual transmission and the parts place lists two flywheel hole sizes - 2.75 Early and a 2.50 Late. How do I find out whether my car is an "early" or "late" without taking it apart?
Also, how do I figure out which speedometer gear to use.
The car has a 3.55 rear and 15" wheels.
Thank your for your help!
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post #2 of 3 (permalink) Old 02-17-2013, 06:40 AM
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they are color coded. a '65 4speed 3:55 ratio is 21 tooth (red), but thats for stock 14" tires.
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post #3 of 3 (permalink) Old 02-17-2013, 03:55 PM
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It seems that V8 Pontiac engines up to 1976 used a 2.75" crank register for the flywheels to mate to.
Information seems to indicate that in 1977, a switch was made to 2.5" (actually might be 2.49" crank register size. Some say "1977 to 1979" was the timeframe for the 2.5" cranks/flywheels.

If your car is known to be stock, I'd say it's pretty likely to have the 2.75" size. But if it's been rebuilt, or you don't know the complete history, it is possible a late model crank could have put into an earlier block...

Another thing is if you do have a small register crank (the 77-79 one), and you want to use a larger/cheaper large bore flywheel, there are allegedly spacers made by somebody to make up the size difference.

Good luck...
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