Ive been reading how to sync a speedometer and find the correct gear for my car and I am hitting a wall. When I drive at an actual speed of 60mph (according to my gps) my speedometer reads 90mph. So then I divide my actual speed of 60 by 90. That gives me a percentage of 66.7. So then I take that percentage and divide by 2.5 percent which is equal to one tooth on the speedo gear which tells me I need to subtract about 27 teeth from my gear. On a TH350 trans, there are only between 34 to 45 teeth which causes my problem. What is the next step I should take, and can anyone instruct me on how to remove the speedo gear so I can at least see how many teeth I am currently running? As far as info goes I am pretty sure the rear axle ratio is 4.11 and my rear tire size is 225/70/15. Also at 60 mph my RPM range is about 3000rpms. Any help would be great. THANKS!

 

Speedometer Gear, Speedometer Gears, Ford, GM, Dodge 700R4
T350 stuff (gears & formula) is about 3/8 way down the page. To get the driven gear out, remove the bolt that holds the keeper tab, and slide the tab off. The speedo gear housing will then slide out. You should be able to tell what gear is inside the tail housing going by the color.

 

Don't you have to pull the driveline and the tailhousing to change the speedo gear?

 

The drive gear on the output shaft, yes. The driven gear, no.

 

From Camaro 69s link.

 

Thanks Camaro 69 for the link. I think Im just gonna order the ratio adapter that slows down the speedometer by 37.5% then add 4 teeth to the driven gear. That should get me close.

 

It only takes pulling the driveline and 4 bolts to pull the tail housing. It's pretty easy to change both gears.