Speedometer pinion,opinion

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gary
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My Cars: '71 GTX Gold Leaf Met.440 A/T

Speedometer pinion,opinion

Post by gary » Tue Jun 19, 2012 9:16 pm

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 :beer:

gcoupe72
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Re: Speedometer pinion,opinion

Post by gcoupe72 » Fri Jun 22, 2012 8:36 am

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 :)

gary
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Re: Speedometer pinion,opinion

Post by gary » Fri Jun 22, 2012 4:49 pm

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 :)

dangina
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Re: Speedometer pinion,opinion

Post by dangina » Sat Jun 23, 2012 2:49 am

Use this chart to figure your pinion:

http://www.moparts.org/Tech/tech/pages/speedo.html
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

gcoupe72
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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

Post by gcoupe72 » Sat Jun 23, 2012 4:54 pm

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 :)
Ok you're reading about 10% fast, so you need more teeth, to slow the speedo down.
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.

gary
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My Cars: '71 GTX Gold Leaf Met.440 A/T

Re: Speedometer pinion,opinion

Post by gary » Sat Jun 23, 2012 6:22 pm

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 :lol: so now i am in the Ballpark!!!! Thanks Again! :beer:

Beepbeep!
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Re: Speedometer pinion,opinion

Post by Beepbeep! » Fri Aug 02, 2013 12:00 am

What if you have a 3 speed manual? Is there a chart for that?
Thanks!

gcoupe72
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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.
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Re: Speedometer pinion,opinion

Post by gcoupe72 » Fri Aug 02, 2013 10:06 am

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.

Moparlar
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Re: Speedometer pinion,opinion

Post by Moparlar » Fri Aug 02, 2013 10:42 am

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

gcoupe72
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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

Post by gcoupe72 » Sat Aug 03, 2013 12:24 am

Woops, I was thinking rpms! :lol:

dangina
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Re: Speedometer pinion,opinion

Post by dangina » Fri Aug 09, 2013 8:04 pm

here you go:

http://www.moparts.org/Tech/tech/pages/speedo.html

*edit someone beat me to it!
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

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