
Speedometer pinion,opinion
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Speedometer pinion,opinion
Hi Everyone,I am trying to get my Speedo.accurate,it is reading about 10mph too fast @40mph.I need help with the gear color and # of teeth for the A/T .Assuming orig.rear end is in car.this is what i know: Rear axle code is D53 on Build sheet 3:23? Suregrip and It is a 8 3/4.Tires are 245 /60 R15.Would that be G60/15? Which color and teeth do i need? Thanks 

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- GTX (RS)
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Re: Speedometer pinion,opinion
Check and see what's in the trans now.
If you're starting from scratch, I'd look for a 32 tooth pinion.
If you have a starting point, figure the percentage of error at your desired speed.
Then go up or down based on that percentage.
More teeth = reads slower
Fewer teeth= reads faster
Example if you're 10mph slow at 65mph that's roughly a 15% difference.
Take your 32tooth pinion multiply by 85% and try a 27 tooth pinion.
If you're 10mph fast at 65mph that's roughly a 18% difference
multiply your 32 tooth pinion x 1.18 and try a 38 tooth pinion
This will get your speed reading closer. Hopefully it will improve your odometer as well,
Though I've never gotten a ticket for a inaccurate odometer
If you're starting from scratch, I'd look for a 32 tooth pinion.
If you have a starting point, figure the percentage of error at your desired speed.
Then go up or down based on that percentage.
More teeth = reads slower
Fewer teeth= reads faster
Example if you're 10mph slow at 65mph that's roughly a 15% difference.
Take your 32tooth pinion multiply by 85% and try a 27 tooth pinion.
If you're 10mph fast at 65mph that's roughly a 18% difference
multiply your 32 tooth pinion x 1.18 and try a 38 tooth pinion
This will get your speed reading closer. Hopefully it will improve your odometer as well,
Though I've never gotten a ticket for a inaccurate odometer

Re: Speedometer pinion,opinion
Thank you gcoupe72 for the info,Here's what i established today .Had wife driving her caravan I drove gtx and walki-talki discovered the following:
Sped.reading GTX Actual spd.Caravan
20 mph 20 mph
45 40
55 50
66 60
76 70
Do these numbers mean wrong spedo gear (teeth) or Spedo out of Calibration? It had a Blk.32 gear i put in a couple years back,it helped. So i could try a 33- 36 tooth gear ? Do you have a chart for the best choice.Thanks in advance Gary '71 GTX
Sped.reading GTX Actual spd.Caravan
20 mph 20 mph
45 40
55 50
66 60
76 70
Do these numbers mean wrong spedo gear (teeth) or Spedo out of Calibration? It had a Blk.32 gear i put in a couple years back,it helped. So i could try a 33- 36 tooth gear ? Do you have a chart for the best choice.Thanks in advance Gary '71 GTX

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- GTX (RS)
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- My Cars: 71 roadrunner
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Re: Speedometer pinion,opinion
400 stroked to 470ci, 3:55 Eaton true trac, slightly upgraded suspension lol
BUILD THREAD!!!! http://www.protouringmopar.com/showthread.php?796-1971-Speedipus-Rex&highlight=speedipus
BUILD THREAD!!!! http://www.protouringmopar.com/showthread.php?796-1971-Speedipus-Rex&highlight=speedipus
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- GTX (RS)
- Posts: 147
- Joined: Fri Mar 11, 2011 11:14 am
- My Cars: 1972 Road Runner originally equipped as lemon twist,400,4spd,air grabber,performance axle pkg.,bk. interior.
- Location: North Carolina
Re: Speedometer pinion,opinion
Ok you're reading about 10% fast, so you need more teeth, to slow the speedo down.gary wrote:Thank you gcoupe72 for the info,Here's what i established today .Had wife driving her caravan I drove gtx and walki-talki discovered the following:
Sped.reading GTX Actual spd.Caravan
20 mph 20 mph
45 40
55 50
66 60
76 70
Do these numbers mean wrong spedo gear (teeth) or Spedo out of Calibration? It had a Blk.32 gear i put in a couple years back,it helped. So i could try a 33- 36 tooth gear ? Do you have a chart for the best choice.Thanks in advance Gary '71 GTX
I came up with 35.2 teeth, so I'd put in a 35 tooth gear.
Also, Chrysler kept using these pinions in trucks well into the '80s. I think gm did also.
If you check with transfer case, and transmission rebuilders, you might find a used one at a good price.
They may even swap for your old one!
Thanks dangina for sharing the chart.
Re: Speedometer pinion,opinion
I wish to thank both of you for the advice
I checked a spare tranny i have for my Dodge A-100 P/U and out came an orange 35 tooth gear
so now i am in the Ballpark!!!! Thanks Again! 
I checked a spare tranny i have for my Dodge A-100 P/U and out came an orange 35 tooth gear


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- GTX (RS)
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Re: Speedometer pinion,opinion
What if you have a 3 speed manual? Is there a chart for that?
Thanks!
Thanks!
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- GTX (RS)
- Posts: 147
- Joined: Fri Mar 11, 2011 11:14 am
- My Cars: 1972 Road Runner originally equipped as lemon twist,400,4spd,air grabber,performance axle pkg.,bk. interior.
- Location: North Carolina
Re: Speedometer pinion,opinion
Hey, since we're talking top gear, which is 1/1 the chart is the same, and for automatics of the same vintage.
Although, since there's slippage with the torque converter, they may need a different size.
Although, since there's slippage with the torque converter, they may need a different size.
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And a roadrunner clone
Re: Speedometer pinion,opinion
Slippage won't affect speedo output since it only looks at output shaft speed. Slippage could mean different engine rpm's at the same speed between auto and stick
1970 440 6 pack 4 speed Superbird
1971 drag car
1972 440 6pack Roadrunner
1971 drag car
1972 440 6pack Roadrunner
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- GTX (RS)
- Posts: 147
- Joined: Fri Mar 11, 2011 11:14 am
- My Cars: 1972 Road Runner originally equipped as lemon twist,400,4spd,air grabber,performance axle pkg.,bk. interior.
- Location: North Carolina
Re: Speedometer pinion,opinion
Woops, I was thinking rpms! 

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- GTX (RS)
- Posts: 394
- Joined: Sat Feb 12, 2011 12:28 am
- My Cars: 71 roadrunner
- Location: lethbridge, ab
Re: Speedometer pinion,opinion
400 stroked to 470ci, 3:55 Eaton true trac, slightly upgraded suspension lol
BUILD THREAD!!!! http://www.protouringmopar.com/showthread.php?796-1971-Speedipus-Rex&highlight=speedipus
BUILD THREAD!!!! http://www.protouringmopar.com/showthread.php?796-1971-Speedipus-Rex&highlight=speedipus