speedometer gear???

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lazer
Posts: 38
Joined: Wed Oct 07, 2020 4:26 pm

speedometer gear???

Post 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

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Joe Travers
Posts: 2424
Joined: Mon Sep 21, 2020 6:23 pm
Location: Louisiana

Re: speedometer gear???

Post 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
Last edited by Joe Travers on Tue Dec 08, 2020 9:31 pm, edited 1 time in total.
Image

1963 1/2 Custom Hardtop
342 stroker, solid roller, T-10, 3.55 posi

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fryedaddy
Posts: 711
Joined: Mon Nov 03, 2014 12:40 am
Location: east tn

Re: speedometer gear???

Post 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.
fryedaddy
Image1966 caliente,428 4 speed,4.11 gears,nitrous,parachute

cbcafe
Posts: 12
Joined: Wed Aug 15, 2018 2:24 pm

Re: speedometer gear???

Post by cbcafe »

Check with Dan williams or David Kee toploaders. They can help you with the right setup for your rear axle ratios.

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