biglg

Marx, what year car are you talking about? You dont have to change anything but the speedo gear on most 3.73 applications. SO what are you referencing too?

ikeybmg

you can get alot closer with a 6tooth drive gear and a 22 (i think) driven gear.

I G Joe

i have 3.73's speedo was way off, grabbed me a speedo gear was easy to find where the gear went popped the old one out and slapped the new one on and bam correct speed.

ikeybmg

mines still like 5mph off a 65 or 70. ive heard the 6 and 22 tooth gets it right on. i think its 22 anyways lol.

biglg

I dont understand why eveyrone is saying you need to change the drive gear. Contact ford motorsports, ford dealer, or search online.

I have never read or heard from any source, other than individuals that say you must/need to change the drive gear?

There are charts all over the net that tell you what speedo gear you need for different year mustangs, with different trans, and different ring and pinions. I posted one of the charts earlier in this post.

Please help me understand why you think 3:73's require a different drive gear?

ikeybmg

i have the 21 tooth for my 3:73's. and its real close but its not just right. everybody knows that it dont put it just right for 3:73's. and i have read that if you swap the 7 tooth for a six and use, if i remember right, a22 tooth driven gear then it will make it aalot closer.

biglg

So I have an 89 5 spd. I just put 3:55's on the car, (for all you 3:73 guys, I drive way to much HWY). I put the 20 tooth speedo gear in. So is there a drive gear that will get me closer to exact? How far off am I now? I should clear this up, I personally didnt put the ring and pinion, nor the speedo gear in. The mechanic did, lol.

Twisted

I'm just about to do the same thing. Did you notice a big difference with the 3.55s?

Liquid_02

I put 3.55's in my car as well about two weeks ago.

Ok, Ignore almost everything above this post, because almost all of it is false, no offence intended, you're all just going off websites selling stuff, but it's all wrong. It's simple math to figure out what gear you need.

Ok here's what you need to do.

You need to find out what drive gear you have in your tranny, yellow (7-tooth) or green (8-tooth) just pop out your speedo cable and take a flash light and take a look inside.

Ok now after you've figured that out... gear ratios....

For 7-tooth:

Gear ratio = Speedo gear / Drive gear

3.00 = 21 / 7
3.14 = 22 / 7
3.29 = 23 / 7 ******
3.43 = 24 / 7
3.57 = 25 / 7 <<<<<
3.71 = 26 / 7

****** Biggest gear you can get
<<<<< Gear you need (3.55)

For 8-tooth:

3.50 = 28 / 8
3.75 = 30 / 8

Notice... Not practical with 8-tooth gear.

Now, here's your other option, upgrade to 6-tooth drive gear (suggested)

For 6-tooth

3.50 = 21 / 6 <<<<<
3.67 = 22 / 6

Now you know what gear you actually need. Just remember, the more teeth you have, the more meshing problems you will have later. I'd say just slam in the 23-tooth gear for now, and if it wears out, upgrade to the 6.

biglg

What is the formula? How did you come up with those speedo gear set ups?


TWISTED,
I have not got my car back from the shop. I am having a lot of different things done to my car. They have had it for 10 days, it should be done today, or tomorrow. I will let you know what I think about the gears once I get the car back.