toploader speedo gears

[Dwight]

Need some help.
My buddy traded for a 67 Fastback Mustang with a toploader HEH-P and the speedo was 15 mph slow. I removed the gear from the speedo cable and the center of the teeth were eat up but it still worked. Put a 16 tooth in because I did not have the 17 that the calculator called for. Drove the car a mile and the speedo stopped working. When we removed the 16 tooth gear the center of the teeth were eat up. I can not see what the color the main gear is. Saturday going to use a bore camera to look at it.
My research lead me to believe that the main gear must match the cable gear. And they have left and right hand gears.

Can anyone explain what I should look for or what I need?

Dwight

[MEATMASTER]

Top loader speedo gears usually have an opposite twist to the teeth... and most likely why they are being chewed up. Compare the angle of the teeth on the gears you are using to this...

Mustang Speedometer Driven Gear Type 3A 18-Tooth 4-Speed Toploader Transmission | CJ Pony Parts

[Dwight]

this link answers all questions

Dwight

Speedo

[DougD]

You appear to have two problems.

First, you are using the wrong driven gear. That's why they are being chewed up. Hopefully you haven't ruined the drive gear, as that will require tranny tailshaft removal to fix.

Remove the driven gear, and hold it in your hand, with the tip pointing up. Now look at the teeth. Do they curve up and to the right, or the left? Whichever you see, you need the other. That's what they mean when they say right hand or left hand gear.

Second, you need to alter the number of teeth to correct the speedo. It's a simple percentage calculation. If you are seeing 15 under at, say, 60 mph, you're off by 25 percent. You need to add teeth to the driven gear to slow the speedo, remove teeth to speed it up.

Here's where I have bought gears before and had good luck:

Speedometer Gear, Speedometer Gears, Ford, GM, Dodge 700R4

You can use a portable GPS to help calibrate your speedo. Works like a charm!

Doug