Speedometer Question???

[pro-street dart]

I now have 31" tires with 4.88 gears on my dart - which will no doubt throw off the speedometer, what speedometer gear would I have to get in order to get it to work close to what it did originally?? Any help appreciated.

[ehostler]

If I've done the math right, you will need the 2538941 (41 tooth) gear.

[ehostler]

I have redone my math and confirmed that you would need approx 41.426 teeth on the gear, to be accurate. If you go with 41 teeth, your displayed speed will be just a little faster than actual.

My base numbers are a 4.56 gear with a 30" tire uses a 40 tooth gear. I got this from http://www.moparts.org/moparts/tech/pages/speedo.html

[pro-street dart]

Thanks for the info!!

[TOOL MAN]

Eholster,

thanks for the info showing all the #'s for the ratios. i asked this question some time ago and the only answer i got was to call mopar performance. this helps

thanks again

tool man

[ehostler]

Glad to have been of help.

I may have seen the earlier request, however I forgot that I had this bookmarked, until I recently saw it, while skimming my bookmarks.

[ehostler]

For any of you that want the math, to calculate the correct speedo pinion, here it is -

((63360/tire circumference)*gear ratio)/76.3 = number of speedometer gear teeth
tire circumference = tire diameter * PI(3.14159)

you should round the number of teeth to the nearest whole number. If you round down, the speedo will read a little fast. If you round up, the speed will read a little slow.

PN for speedo gears are 25389XX (where XX=number of teeth)

I set this up in a spreadsheet and I just have to punch in the rear ratio and the tire diameter. it then gives me the correct number of teeth.

[ehostler]

The PNs for the speedo pinion have changed. Here is the new PN listing. Many thanks go out to John Kunkel, for this info.

Originally posted by John Kunkel
TOOTH COLOR PN#

24 WHITE 3410024
25 BLUE 3410025
26 RED 2538926
27 WHITE 52068149
28 BLUE 52068150
29 BLACK 52068151
30 YELLOW 52068152
31 GREEN 52068153
32 BLACK 52068154
33 YELLOW 52068155
34 GREEN 52068156
35 ORANGE 52068157
36 RED 52068158
37 WHITE 52068159
38 BLUE 52068060
39 GREEN 52068061
40 ORANGE 52068062
41 RED 2538941
42 WHITE 2538942
43 BLUE 2538943
44 BLACK 2538944
45 Yellow 2538945

[ehostler]

Originally posted by John Kunkel
The adapter in the tailhousing must be installed with the hash mark next to the tooth count aligned with the raised dot on the tailhousing. See pic in attachment.