Speedo gear help

**drdave69** · #1 06-19-2022, 07:41 PM

I finally got around to pulling my turbo 400 trans pan off to replace the kickdown solenoid. While I am working on it I decided to pull the speedo gear out since the speedo is off since the rear gears were changed. What I have researched is that I need a 24.38 tooth driven gear but I want to ask some experts.
I have a yellow drive gear in the trans with 11 teeth. The axle ratio is now 3.08 and the tires are 28 inches high (p235/70/15).
FYI, the speedo gear I pulled out is yellow with 34 teeth.

**John Brown** · #2 06-20-2022, 06:02 AM

I'm thinking a ratio adapter is gonna be in order instead of a gear change. Look around and see what you come up with.

PATC transmissioncenter.net/product-tag/speedometer-gears

**scuncio** · #3 06-20-2022, 01:22 PM

The calculation seems correct. Do you know the exact tire diameter? I suspect it’s less than 28”.

**drdave69** · #4 06-20-2022, 01:41 PM

The tire diameter is based on the tire size. I did not physically measure it.

**Lynn** · #5 06-20-2022, 01:56 PM

I come up with 27.95, obviously close to 28.

**drdave69** · #6 06-20-2022, 09:54 PM

I drove around town today to find the speedo gear I may need and learned a little more about this task. Trans guy said that putting a smaller (less teeth) gear in would make it run at a higher speed than it already does. My speedo gear housing is also not compatible with a smaller gear. This is just getting too complicated so I purchased a 39 tooth gear (brown) from him and will try it later.