Speedometer gear

[summitlt]

I have 31s and 4.10s. Two sites said that a 38tooth is the right size. I have a 39 tooth and its off about 5mph at 60. Should I get a 38t or a 37t?

 

[dmillion]

Is it reading too high, or is it reading too low? If it's reading high then you need a gear with more teeth. If it's reading low then you need a gear with fewer teeth.

 

[summitlt]

Its reading low, I jsut wanted a pointer on what size to use

 

[hippymill]

also check to make sure the sensor is indexed in the housing correctly. mine was reading a little off, but the sensor retainer wasn't seated in the grooves. It was rotated slightly counter clockwise, and was reading about 9 miles off with 31's and a 38 tooth gear. Set it correctly and it reads almost spot on. GPS says it reads 1 mph slow now.

 

[dmillion]

The math is pretty simple. It's reading 55 when you're actually going 60.

55 / 60 = .917

You have a 39 tooth gear.

39 * .917 = 35.76

You need a 36 tooth gear. Then it will read about 60.5 when you're actually going 60. If you use a 37 tooth gear it will read about 58 when you're actually going 60.

Of course, what hippymill said about making sure it is indexed correctly and fully seated into the transfer case also applies. That alone might solve your problem.

 

[summitlt]

Thanks for the formula, if I had found that I would have used that.

Thanks.