speedometer gear question

[SHX669]

I'm trying to get an accurate or close as possible reading with the new speedometer head I installed in the '76.
I went with a 16 tooth speedo gear ; which i understand is the fewest tooth count available ; and the speedometer is still about 10% off - on the low side - 50 mph on speedo is actually 55 mph.
Did Ford put different ratio drive gears in the TC output housings? I'm running 4.10s with 35" tires so it's a little on the "tall " end of things and I expected to have to go with 18-20 tooth .
Short of dropping to 4.56 gears is there a fix or do I just remember I'm 10% off ? At least that's better than 13% - easier math - LOL . { Oh - the local cops use any excuse to pull these "old" rigs over , check for insurance,current tags , safety etc. I know a couple of guys who got pulled over for no license plate light so 5 miles over speed limit is a guaranteed "stop and talk"}

 

[Broncobowsher]

Yes, 2 different driving gears.
Viperwolf made a nice chart that fives all the tooth combos. It is around on this site, I don't have a link in front of me. Give it a few hours, someone will post it here soon.

 

[Viperwolf1]

You need a 7 tooth drive gear.

 

[SHX669]

Thanx for the info - now I need to find a source for the 7 tooth gear.

 

[Viperwolf1]

Thanx for the info - now I need to find a source for the 7 tooth gear.

Not available new. You'll need to find one in someone's D20 parts pile.

 

[SHX669]

Hey - thanx again!

 

[RPM289]

Are the gears color coded or got to try to count teeth?

 

[Viperwolf1]

Are the gears color coded or got to try to count teeth?

The plastic ones are colored. Light blue for 7 teeth, green for 6 teeth. There are also steel versions of each. It is very difficult to count teeth on them.