speedometer gear tooth count

Does anyone know what tooth count I'd need for D20/3.73/33" tires to get as accurate as possible? I need to buy the cable and the gear that goes in the transfer case. Are all speedo cables pretty much the same quality? Thanks.

 

Never mind...found my answer here:
http://www.quadratec.com/jeep_knowledgebase/article-46.htm

 

Tnx for posting.

 

incorrect for Jeep D20
wrong gears, wrong everything

 

maybe this
http://www.wildhorses4x4.com/product/Speedometer_Drive_Gear

 

Thanks a lot Ron!

 

still incorrect for Jeep D20 .....

 

Ok thanks

 

I think the goal is to have the speedometer cable turn 1000 turns per mile.
With 33" tire times pi / 12" to get tire circumference.
33 * 3.14 / 12 = 8.6393725 feet
How many tire turns per mile?
5280 / 8.6393725 = 611
Drive shaft turns per is tire turns per mile time axle ratio.
611 * 3.73 = 2280.
To get 1000 turns your speedometer gear ratio needs to be about 2.3 to 1.
The drive gears are 4 or 6 teeth that I've seen.
The driven gears are hard to find but it looks like 14 would be close if you had 4 the drive side.

 

Here's a link to an easy to understand method for determining which gear to use. It's from an Ohio Early Bronco website. I assume the calculations are correct.

http://www.broncohio.com/tech/calculations.html

 

Try this shop. http://www.willysworks.com/

I read a post on jeepforum.com from this past June discussing the same problem. Said this shop had the part at a reasonable cost.

 

got around to digging D 20 out to look at this mysterious speedo drive gear . now this is a 79 model

 

The one shown is actually the driven gear. The drive gear is inside the output housing, fits on the output shaft, and acts as a spacer between the two output bearings. The tooth counts and diameters of both come into play. They must be compatible with each other or they will not work or will self destruct.

 

over or under drive speedometer correction unit . most speedometer shops use this . if its too much trouble to change out stock speedometer gears , drive and driven as nick pointed out

 

I've been reading about those...I'll figure something out soon. Thanks Ron!