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Re: Let's do speedo and rear gear math!
[Re: Bull1tt]
#1892322
08/15/15 11:51 AM
08/15/15 11:51 AM
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Joined: Jan 2004
Posts: 2,103
East Coast, NJ
fig426
top fuel
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top fuel
Joined: Jan 2004
Posts: 2,103
East Coast, NJ
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Approximately 205/70/14 25.30 diameter.
Chris from New Jersey
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Re: Let's do speedo and rear gear math!
[Re: fig426]
#1892373
08/15/15 01:23 PM
08/15/15 01:23 PM
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Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
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What I'd do is get the exact dia from "rollout" then go to the MP chart. then you'd have your dia and 3.73 ratio. someone here posted the chart that goes to the tenths of tooth count, I'd find it or see if someone will repost it. IE if says you need a 26.2 tooth pinion for your dia then find a 26 tooth pinion and if you need a 26.7 tooth pinion then find a 27 tooth pinion & if you have an early trans then yes you'll likely need the adapter
live every 24 hour block of time like it's your last day on earth
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Re: Let's do speedo and rear gear math!
[Re: Bull1tt]
#1892376
08/15/15 01:31 PM
08/15/15 01:31 PM
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Joined: Sep 2007
Posts: 14,889
up yours
Supercuda
About to go away
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About to go away
Joined: Sep 2007
Posts: 14,889
up yours
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You cannot use later pinion math for early pinion choices. The number of teeth on the output shaft is different and will throw the math off if you try to extrapolate from later pinion calculators.
They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.
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Re: Let's do speedo and rear gear math!
[Re: Supercuda]
#1892395
08/15/15 01:50 PM
08/15/15 01:50 PM
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Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
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You cannot use later pinion math for early pinion choices. The number of teeth on the output shaft is different and will throw the math off if you try to extrapolate from later pinion calculators. good clarification. OP, with that early trans & pinion selection being limited (as you know) you might try evilbay or the guys at www.slantsix.org or FABO and somebody has to be selling those adapters
live every 24 hour block of time like it's your last day on earth
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Re: Let's do speedo and rear gear math!
[Re: Bull1tt]
#1892397
08/15/15 01:54 PM
08/15/15 01:54 PM
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Joined: Sep 2007
Posts: 14,889
up yours
Supercuda
About to go away
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About to go away
Joined: Sep 2007
Posts: 14,889
up yours
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You shouldn't have a problem getting a ratio adapter, http://imperialservices.net/Bparts.html
They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.
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Re: Let's do speedo and rear gear math!
[Re: Bull1tt]
#1892503
08/15/15 05:36 PM
08/15/15 05:36 PM
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Joined: Jan 2003
Posts: 25,748
Rio Linda, CA
John_Kunkel
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 25,748
Rio Linda, CA
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You'd need a 23-tooth pinion and there ain't no such thing. There are inline ratio adapters that can be installed in the speedo cable.
The INTERNET, the MISinformation superhighway
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Re: Let's do speedo and rear gear math!
[Re: lewtot184]
#1900773
08/28/15 12:10 AM
08/28/15 12:10 AM
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Joined: Jan 2005
Posts: 1,606
Pgh, PA
Bull1tt
OP
top fuel
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OP
top fuel
Joined: Jan 2005
Posts: 1,606
Pgh, PA
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how did someone figure .67 ratio reducer? what pinion are you using now? i don't think the math is right. Here's what we did. Drove the car with a GPS showing the actual speed. At actual 40 mph, speedometer reads 60. At 50 mph speedo reads 75, and at actual speed of 60 mph speedo reads 90. In each example, divide the actual mph by the reading of the speedometer. In this case, it works out to a .67 reduction to match the speedometer to the GPS. Having a ratio reducer built since there is no factory gear available to correct the difference. This is an early (63 BB 727) transmission. They are different from the '66 up units. Has an 8 tooth drive gear and a 16 tooth gear on cable now, car updated with 3:73 rear gear and tire at 26.5" diameter. This should work. It may be a little pricey, but they are the only game in town for the 62-65 trans.
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Re: Let's do speedo and rear gear math!
[Re: lewtot184]
#1901174
08/28/15 04:11 PM
08/28/15 04:11 PM
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Joined: Jan 2003
Posts: 25,748
Rio Linda, CA
John_Kunkel
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 25,748
Rio Linda, CA
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how did someone figure .67 ratio reducer? what pinion are you using now? i don't think the math is right. Small tires and high (numeric) axle ratios generate speedo cable speeds that can't be corrected with the available 16-21 tooth early pinions. The .67 reduction allows the user to alter the normal math to choose the correct pinion. As I stated earlier, the OP's combo would require a 23-tooth pinion which was never available so the .67 reduction would call for a 15-tooth pinion which, also, was never available; so a 16-tooth would be the closest. That's why an inline reducer is more practical, they allow for a wide variety of reduction ratios.
The INTERNET, the MISinformation superhighway
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Re: Let's do speedo and rear gear math!
[Re: John_Kunkel]
#1901178
08/28/15 04:15 PM
08/28/15 04:15 PM
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Joined: Jun 2008
Posts: 3,916
usa
lewtot184
master
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master
Joined: Jun 2008
Posts: 3,916
usa
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how did someone figure .67 ratio reducer? what pinion are you using now? i don't think the math is right. Small tires and high (numeric) axle ratios generate speedo cable speeds that can't be corrected with the available 16-21 tooth early pinions. The .67 reduction allows the user to alter the normal math to choose the correct pinion. As I stated earlier, the OP's combo would require a 23-tooth pinion which was never available so the .67 reduction would call for a 15-tooth pinion which, also, was never available; so a 16-tooth would be the closest. That's why an inline reducer is more practical, they allow for a wide variety of reduction ratios. john, i'm very familiar with the ratio reducers. i use one in my '65 coronet. it just seems to me that .67 is very steep, even with a 16 or 17 tooth pinion.
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Re: Let's do speedo and rear gear math!
[Re: Bull1tt]
#1901182
08/28/15 04:23 PM
08/28/15 04:23 PM
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Joined: Jun 2008
Posts: 3,916
usa
lewtot184
master
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master
Joined: Jun 2008
Posts: 3,916
usa
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how did someone figure .67 ratio reducer? what pinion are you using now? i don't think the math is right. Here's what we did. Drove the car with a GPS showing the actual speed. At actual 40 mph, speedometer reads 60. At 50 mph speedo reads 75, and at actual speed of 60 mph speedo reads 90. In each example, divide the actual mph by the reading of the speedometer. In this case, it works out to a .67 reduction to match the speedometer to the GPS. Having a ratio reducer built since there is no factory gear available to correct the difference. This is an early (63 BB 727) transmission. They are different from the '66 up units. Has an 8 tooth drive gear and a 16 tooth gear on cable now, car updated with 3:73 rear gear and tire at 26.5" diameter. This should work. It may be a little pricey, but they are the only game in town for the 62-65 trans. i'll assume the 16 tooth pinion was with a 2.76 rear gear. 2.76 divided by 3.73 (new gear) is .74. my take is a .74% reduction. o'well, what do i know?
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Re: Let's do speedo and rear gear math!
[Re: lewtot184]
#1901766
08/29/15 11:53 AM
08/29/15 11:53 AM
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Joined: Sep 2007
Posts: 14,889
up yours
Supercuda
About to go away
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About to go away
Joined: Sep 2007
Posts: 14,889
up yours
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i trust the math, not the gps. Did you show your math?
They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.
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Re: Let's do speedo and rear gear math!
[Re: lewtot184]
#1901960
08/29/15 06:20 PM
08/29/15 06:20 PM
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Joined: Jan 2003
Posts: 25,748
Rio Linda, CA
John_Kunkel
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 25,748
Rio Linda, CA
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i trust the math, not the gps. Problem is, the math only guarantees an accurate odometer not an accurate speedometer. Many speedo errors are in the head itself.
The INTERNET, the MISinformation superhighway
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