Correct Speedo Gear

[mark69sportsroof 31]

Hi Everyone, 

 

I'm trying to figure out the correct speedo gear for my 69.  It seems that I have seen a formula to determine the correct gear but I do not remember where or when I saw.  Listed below is the key information if that helps.

 

FE 390 stroked out to 445ci

 

T-5 transmission

 

3:50 Pos rear end

 

No A/C

 

Weight - approx 3400 pounds

 

Thanks Mark 

[jgkurz 52]

Hi Everyone, 

 

I'm trying to figure out the correct speedo gear for my 69.  It seems that I have seen a formula to determine the correct gear but I do not remember where or when I saw.  Listed below is the key information if that helps.

 

FE 390 stroked out to 445ci

 

T-5 transmission

 

3:50 Pos rear end

 

No A/C

 

Weight - approx 3400 pounds

 

Thanks Mark 

 

 

You'll need to know your rear tire diameter and the "drive" gear inside the T-5. These tools should help.

 

http://www.wallaceracing.com/tire-aspect-calc.php

 

http://www.classic-cougar.com/tools/speedocalc/speedocalc.php

[BillC 38]

Mark,

I went through this when wheels were changed from 14" to 15".

Here's a simple way to determine the correct speedo gear.

I used a GPS to get the correct speed. Take your speedo cable out of the transmission. Count the teeth on the gear. Add teeth if speedo reads too fast. One tooth equals 5 mph. Deduct teeth if speedo is too slow.

 

P.S. Change the gear retainer while your doing the gear. They are very brittle and will probably break when you remove the gear.

[mark69sportsroof 31]

Thanks guys for the info.  I drove it on the street and highway and used my GPS and my speedo was 10 mph was 10 mph faster then the GPS.  I have a a 19 tooth gear so I need to get a 21 tooth gear if I read the Bill's response.  Mark