Thank you to RDean for this excellent article describing how he manufactured his own custom gears.

Automatic trans 1985 Fiero
You will also need a rotary table (Mine is a 6")


Started with round plastic stock and put in the lathe. (I don't know what it is made of just had it laying around)




Use your old gear as a pattern and this is what you end up with.


I used a set screw to lock the gear to the VSS shaft.


Next I made a spindle to mount the gear on with a #2 MT


Measure the angle of the teeth on the original gear and mount the rotary table at that angle.


Grind your cutter to match the gear shape you want. (Trial and error method on scrap material)


Set the center line of the cutter to the center line of the gear and move the table back and forth to cut.


I wanted 28 teeth and my table has 72 turns for 360 degrees so the math turns out like this.
72 divided by 28 = 2 16/28 turns.
My table does have a section of 28 holes so for each tooth I will turn the table handle 2 full turns and then another 16 holes on the 28 section. Hope that makes sense!

On the headlight gear I wanted 40 teeth so the math works out like this.
72 divived by 40 = 1 32/40 or 1 4/5
Using the 25 hole section you count 20 holes to get 4/5 of that section.
Turn the handle 1 full turn and 20 hole further for each tooth.

Results


I went to a larger tire and wheel on the rear and it calculated out to be about 10% larger. So at 60 miles a hour showing on the speedo i was actually going 65. I made the driven gear 10% smaller so it would turn 10% faster than before and indicate 60 at 60 miles per hour.

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