Speedometer Gears

[Byron Gray]

I got a 904 from a 78 lebaron im going to use in my 67 dart. I took the gear out of a slant 6 904 I have and here's what I have and noticed the gear is smaller and seems it won't touch the outputshaft. Is there a bigger gear I can get?

 

[Byron Gray]

Pretty sure I just figured out what I need. I had ordered a new gear for a trans in my other car from cope racing and it is the same size and the gear in the 78 trans. Figured out the tooth count I needed and got another from cope so see when it comes in if it will work.

 

[Professor Fate]

The size of the gear is relative to the tooth count. The tooth count is related to your rear end gears and tire size.
Now, look at the gear pinion adapter. See how the speedo cable attachment is off center? That is so it can be rotated to accomodate different sized gears. There are markings on the tailshaft and gear pinion adapter that show you where to rotate it to for your particular gear size/tooth count, so it engages properly.
You need to figure out what size gear (tooth count) that you need for your setup, and install it properly; or your speedometer will NEVER read correctly.
Mopar Speedometer Gear Selection Guide - MyMopar.com

Notice at the bottom of the above picture, there are numbers stamped into the adapter that correlates to the numerical tooth count. Rotate the adapter until the proper number range is at 6:00. Then tighten it down.

 

[Byron Gray]

The size of the gear is relative to the tooth count. The tooth count is related to your rear end gears and tire size.
Now, look at the gear pinion adapter. See how the speedo cable attachment is off center? That is so it can be rotated to accomodate different sized gears. There are markings on the tailshaft and gear pinion adapter that show you where to rotate it to for your particular gear size/tooth count, so it engages properly.
You need to figure out what size gear (tooth count) that you need for your setup, and install it properly; or your speedometer will NEVER read correctly.
Mopar Speedometer Gear Selection Guide - MyMopar.com

View attachment 1715609977
Notice at the bottom of the above picture, there are numbers stamped into the adapter that correlates to the numerical tooth count. Rotate the adapter until the proper number range is at 6:00. Then tighten it down.

thank you i did not know that. i did the calculation for the right tooth gear i need.