I'm trying to figure out the ratio I need for my speedo gear, and I'm using the NPD catalog method (page 90) ->

http://npd.dirxion.com/WebProject.asp?BookCode=fir08pfp#

They mention that I need to count the teeth on the drive gear, but I'm not sure what gear that is. Help!

The speedometer DRIVE gear is on the tailshaft of the transmission. You can't remove it without removing the tailshaft housing. The speedometer DRIVEN gear is the one your speedometer cable plugs into. It can be removed by removing the plate where the speedometer cable screws on. The number of teeth on both gears matters.

So, from what I understand, the gear that they're referring to is the gear that seats into the driven gear at the housing?

I also found this equation, which seems WAY easier. Has anyone used this?

TH400, TH350BOP, 700-R4: Speedo driven gears have from 34 to 45 teeth. Each tooth added lowers the speedo reading about 2.5%. Each tooth removed raises the speedo reading about 2.5%. In our example, we want to lower the speedo reading from 60mph indicated to 52mph indicated. We need to add teeth to lower the reading by spinning the speedo cable slower. Remember, one tooth = 2.5% so we need to add about six teeth. (15.4%/2.5% = 6.2 teeth).

Instead of doing all that math, how about having the Factory speedo gear charts for Pontiacs as a starting point?

Then you can modify the gear selection for the size of wheel/tire you have.

Fred's Pontiac Speedo Charts

I used a chart like that on Vikki's site and the drive gear I needed was discontinued/out of stock/etc. I ended up with a set of gears my local transmission shop set me up with that is close. With the compromised gears, 30 mph shows 32 mph on the speedo, and 70 mph shows 75 on the gauge. You can check it by using a GPS. My Magellan tells me how fast I'm going. A Garman does too.