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  #1  
Old 05-31-2003, 12:58 PM
69baby 69baby is offline
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Help speedo pinion gear

can someone help me here? i have a 69 charger with 4:10's. it has p255/60/r15's on it. my book said that 15 inch tires came with the 426 only. the speedo didn't work when bought, so i replaced the gear with a new one, same 32 tooth, this is wrong because it apple cored, nothing works. i've read the forums, found the pinion chart. now the 4:10 uses a 40 ta 43 tooth, how do i get the right gear?


thanks 69 baby <
happy moparing
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  #2  
Old 05-31-2003, 01:28 PM
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ehostler ehostler is offline
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Straight from my post that is in the Tech Archives http://www.moparchat.com/forums/show...&postid=372505

Quote:
Originally posted by 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.
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Old 05-31-2003, 01:47 PM
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ehostler ehostler is offline
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Here's the simple spreadsheet. Just input the tire diameter and the axle ratio and it will give you the number of teeth for the pinion gear.

I had to make it into a .zip file as the site won't let me upload an xls file.
Attached Files
File Type: zip speedo.zip (1.9 KB, 14 views)
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Old 05-31-2003, 05:43 PM
John Kunkel John Kunkel is offline
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By "apple cored" do you mean it sheared the teeth off of the plastic gear? If so, the gear wasn't indexed correctly.

The correct gear for this setup is a 40 tooth (current P/N is 52068062) and 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 below.

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Old 06-01-2003, 12:40 AM
djswwg djswwg is offline
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Ehostler, I'm trying your formula but don't understand exactly what it is. What is the little star for? Sorry for being such a dunce-could you maybe put it in english rather than the math formula version? Thanks.....djs
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Old 06-01-2003, 01:06 AM
69baby 69baby is offline
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Unhappy speedo pinion

they say theres no dumb questions, but i sure feel like an idiot.
i down loaded the zip but my puter didn't like it. i went back to all the forums i could get and couldn't make heads or tails of them.
by apple cored it looks like you ate an apple, outside edges full, the middle narrow. thats the way the one i was replacing looked like too. i installed it the way the manual said. with the "proper tooth range number 6 o'clock carefully press into housing" put
retainer in slots tap and tighten bolt.
if 40 is what i need how did you get it?
thanks for all your help!!!! pvanlannen@excel.net

lost but not forgotten

again thanks 69 baby

happy moparing
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  #7  
Old 06-01-2003, 03:35 AM
George G. Leverette George G. Leverette is offline
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The gears can be purchased from the dealers, some of the counter jocks can give you the correct setup for your application. They are even more helpful if you point them in the right direction.
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  #8  
Old 06-01-2003, 01:57 PM
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ehostler ehostler is offline
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Quote:
Originally posted by djswwg
Ehostler, I'm trying your formula but don't understand exactly what it is. What is the little star for? Sorry for being such a dunce-could you maybe put it in english rather than the math formula version? Thanks.....djs
If you use a spreadsheet program or the scientific calulator that is in Windows, the * is multiply.

For a regular calculator or for those doing this in pencil -

((63360/tire circumference) X gear ratio)/76.3 = number of speedometer gear teeth

tire circumference = tire diameter X PI(3.14159)
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Old 06-01-2003, 06:00 PM
djswwg djswwg is offline
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Thanks Ehostler for the clarification. It all works out now. ....djs
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Old 06-02-2003, 12:05 AM
69baby 69baby is offline
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Thumbs up

thanks again but it's not working for me.

69 baby

happy moparing
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  #11  
Old 06-02-2003, 09:46 PM
djswwg djswwg is offline
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69baby; try this. divide 63360 by the circumference of your tire. You can figure out the circumference one of two ways. Measure the height of the tire, lets say 28 ", then multiply by 3.1416. The answer is 87.96. To verify, wrap a piece of string around the tire, mark it where the ends meet, then lay it out and use a tape to measure. Take that figure (720.32) and multiply by your diff gear ratio,(lets say 3.55). The answer to that is 2,557.16. Divide by 76.3, the answer is 33.51. Now round up to the next whole number which is 34, and thats the number of teeth needed for your speedo drive gear. Hope this helps you..................djs
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  #12  
Old 06-06-2003, 12:43 AM
69baby 69baby is offline
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Hi again all,
Thanks again. I did the math, and guess what it works. I don't know what I was doing wrong, I went back and did the math from both of you and got the same answer. Maybe I was just trying to hard. I ordered parts today and I feel better now. I will keep this formula for future reference. I off to my next project, electronic ignition upgrade.

69 baby

Happy Moparing!
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