Road Runner Nest

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

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

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

Use this chart to figure your pinion:

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

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.

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!

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

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.

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

Woops, I was thinking rpms!

here you go:

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

*edit someone beat me to it!