Speedometer adjsutment

[66GTOLVR]

Hey Goat Gods I need some help getting my spedometer back to calibration or as close to as possible. I removed a ST300 tranny and installed a TH400. Also, put in a 3.23 posi and i have 14" tires. How do i get the speedo back to some what of accuracy? The driven gear in the TH400 is a red in color (I believe 37 teeth).

Was told to drive and look at speedo when on a mile marker and when i pass the next one look to see how far i have driven. then multiply by 1.3 times the driven teeth. That equals to 48. So do i need a 48 tooth driven gear to make me accurate????

Need help on this one. Any suggestions??

Thanks,

Larry
66 GTO
White Tiger

[THOR]

I changed trannies and my speedo was way off.
For about $110, I had tacoma speedometer fix it up with no hassle.
They put my '70 GTO on a speedo dynomometer. Before, it was off by 20 mph when doing 110 mph. Now it's within 3/10 of a mile per hour at 70 MPH.

[66GTOLVR]

Did they adjust your needle only or what did they do? Was told that you can adjust the needle only and the odometer still goes fast and doesn't record accurately the mileage.

That sound a little steep to adjust. Any other words of wisdom out there like adding 1-2 teeth on driven gear etc...

Larry

[Icelander]

The only way I've ever seen it done is to change out the driven gear at the transmission. To adjust the speedometer at the gauge itself, you'd have to open it up and adjust the magnet within the little cup at the pivot of the needle. Not a small feat! When the bushings go out on a speedo you'll see it as a wavering of the needle. The worse the waver, the more worn the bushing is. The little magnet is attached to the speedo cable and exerts force on the spring loaded needle.

Did I give you more information than you wanted to know?

Kendall

[Red_Rider]

In the Pontiac Restoration guide, around page 300 it gives various gear colors for different rearends. under 1966, 3.23 is 39 teeth, Brown; 3.08 is 37 teeth, red; 3.55 43 teeth, purple. for other ratios like 3.36, 3.90, & 4.33, they show the gear and an adapter.

At one time, I hit a website that showed how to calculate the proper gear, but don't know where it was. :roll:

[66GTOLVR]

Presently I have a red 37 tooth in the newly installed TH400 tranny. In the restoration book does it show the 66 with 3.23 and a TH400 instead of a two speed tranny? That will probably make a difference since the TH400 has 3 gears and a deeper 1st with different gearing. I also have 14" tires if that makes a difference.

:?:

Larry
66 GTO
White Tiger

[Red_Rider]

The book only shows gears for Automatics years 64, 65, and 66. 4 speeds 64-70. Don't worry about the number of gears in the transmission, the speedomometer reading is taken at the tailshaft and reflects the driveline speed. However, the number of teeth that drive the speedometer gear can vary. Below are two websites that offer some information. the first tells you how to determine which gears to use. The second shows which gears are available.

http://www.bgsoflex.com/speedo1.html
http://www.transmissioncenter.net/speedometer_calibration_______va.htm