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speedometer gear???
Posted: Tue Dec 08, 2020 6:26 pm
by lazer
I have a 66 mercury comet 390 3 speed stick, I am changing it to a 4 speed. I got a rug-j trans with a c70 tail, what do I do for the speedometer gears?/ Also I'm going to change it to a 3.55 posi rear, I don't have that yet but soon. Also any suggestions on the rear? Thanks
Re: speedometer gear???
Posted: Tue Dec 08, 2020 7:09 pm
by Joe Travers
Dealerships used to calculate it for you back in the day. Try this out-
https://www.tciauto.com/speedometer-gear-calculator
JT
Re: speedometer gear???
Posted: Tue Dec 08, 2020 7:20 pm
by fryedaddy
your 66 should have a 28 spline open rear.it would be nice if you had a 67 gt rear,they had 31 spline posi.
Re: speedometer gear???
Posted: Wed Dec 09, 2020 9:21 pm
by cbcafe
Check with Dan williams or David Kee toploaders. They can help you with the right setup for your rear axle ratios.