Speedo Maxes At Around 20 Now...

I have to assume I used the wrong gear in my Dana 18 when I rebuilt it because now I only see a max speed of 20. I built a tcase using parts I had around. I have two other gears but I don’t know which came from my stock tcase. Any suggestions on how to figure out which gear will fix this?

 

As I recall, the Dana 18 shifts high-low with one shift rod, and the front axle with the other. I'd guess you have it put together wrong and it's always in low range now. Or maybe the only combo that meshes is low range. Different gears have different tooth angles and won't necessarily mesh. The widely available TSM shows how it's assembled, and you can identify the geara from the chart on the Novak site. They each have a Dana and Jeep PN on the gears. The Novak Guide to Dana 18 & 20 Gears Interchange 1941-1979

 

My initial read on this was that the speedo is only showing 20 and assumed it was the speedo gears he was asking about, but after timgr's response, maybe good to clarify whether the Jeep will only actually do 20 mph, or is the speedo topping out at 20 mph no matter how fast you go?

 

Maybe it's just an indicated 20. We need a response from the OP. I kinda doubt you could get that low an indicated speed with any of the available speedometer gears.

 

Loose yoke? The gear is mashed into place with the yoke if it’s loose the gear could spin on the shaft.

 

The Jeep can go 90MPH but the speedometer will show about 20MPH or so. I am thinking the yoke is not holding the gear in place. Perhaps I need to measure and find a slightly thicker gear. I have a couple. I know I installed 1 gear initially and it would not allow me to turn the rear yoke. At the time I figured that was the wrong speedometer gear so I used a slightly less thick one and everything spun smooth. Now I think I need to find one that is a happy medium thickness.

 

How tall were the 8.45x15 tires back in the day?