Hello.
I have a 82 trans am with a TH350 and 3,73 axle ratio.

My meter is showing around 23% too fast.

I'm planning to solve this by changing to a driven gear with 24 or 25 tooth (today I have a 20 tooth driven gear).

But will these gears fit with my drive gear?

According to this page; http://chevelleengineer.home.comcast...eer/speedo.htm there are 3 different drive gear diameters that require matching driven gears. And there is a 20-tooth-driven-gear-version for both the 1.76" and 1.84".

I need to know my drive gear OD. Question: Is there an easy way to determine what drive gear diameter I have?

Any help, ideas is greatly appreciated.

 

You're not from the United States are you?

 

You need to know your drive gear tooth count.
And you'll also need to know the driven gear diameter.

 

Jayhawk: No. I''m from sweden. A beautiful little country in the north.

JMD:I know I need to know my drive gear tooth count. Do you (or anyone else) know an easy way find out?

 

Put the rear on jackstands and the trans. in neutral.
Remove the driven gear.
Mark one drive gear tooth with a sharpie.
Rotate the driveline while counting the teeth on the drive gear.

 

And,
From your other thread,

No, changing speedometer gears will not correct an odometer correct / speedometer incorrect issue.

 

Thank you for all your help!

The space where my speedometer cable goes in is really tight. It will be hard for me to get in there even with the smallest sharpie.

Instead I did like this. And would like to hear your comments on this.

1. I know from my GPS that my odometer shows 23% to much. (I drove 19.6 KM according to my GPS. ODO showed 25.4222 KM. (19.6/25,4222=0,77)

2. My driven gear is 20 tooth. Axle ratio 3.73. Rear Tire Diameter 30.43.(P245/80 r15)

3. In order to make my odometer (and speedo) accurate i would need around 4.6 more gears (according to http://chevelleengineer.home.comcast...eer/speedo.htm which says that each tooth added on the driven gear make the speedo read around 5% slower (4.6*5=23).

5. I went to this site: http://wallaceracing.com/speedo-calculator.php, entered my data BUT in the driven gear field i wrote (20+4.6) 24.6 since that would be correct for my car.

6. The calculator says I need a drive gear with 9.95 tooth.

7. I therefore must have a 10 tooth drive gear. And the OD on all th350 drive gears are 1.84".

8.I wont be able to fix my speedo issues with just replacing the driven gear since the highest driven gear tooth count avaible is 22 for a 1.84" drive gear.


QUESTIONS:
1. Is there something I've missed taking into calculation?

2. Is there a good guide somewhere for how to replace the drive gear on a firebird without removing the tranny?