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REAR END GEAR RATIO- A100

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hastingsman

Number of posts : 68
Location : south of Grand Rapids, Mi.
Age : 66
Registration date : 2015-11-07

REAR END GEAR RATIO- A100

Post by hastingsman on Sat Jul 01, 2017 6:16 pm

I'm running about 2000 rpm at 55 mph with a Chevy 305 automatic in my '64 A-Pup. Wondering what the gear ratio of the stock rear end is-?-

Thanks-
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68bigblock

Number of posts : 38
Location : Alberta
Registration date : 2016-03-19

Re: REAR END GEAR RATIO- A100

Post by 68bigblock on Sat Jul 01, 2017 9:37 pm

assuming you don't have a OD trans and about 27" tire i would guess around 292
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uncle ron

Number of posts : 80
Location : orange,calif.
Age : 70
Registration date : 2012-05-31

Re: REAR END GEAR RATIO- A100

Post by uncle ron on Sat Jul 01, 2017 10:27 pm

hastingsman wrote:I'm running about 2000 rpm at 55 mph with a Chevy 305 automatic in my '64 A-Pup. Wondering what the gear ratio of the stock rear end is-?-

Thanks-
Try this site https://tiresize.com/gear-ratio-calculator/ Ron
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69

Number of posts : 131
Location : Germany, Nds
Registration date : 2016-10-18

Re: REAR END GEAR RATIO- A100

Post by 69 on Sun Jul 02, 2017 2:13 am

The stock rear end is 3.23, casting typically is 741 (on the driver side of the rear end, input shaft). But the casting does not tell you about the ratio.

There's plenty of information:

https://www.hemmings.com/magazine/mus/2004/10/Mopar-8-3-4-inch-rear-ends/1280934.html
http://www.moparwiki.com/index.php?title=Rear_Axle_8.75%22
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hastingsman

Number of posts : 68
Location : south of Grand Rapids, Mi.
Age : 66
Registration date : 2015-11-07

Re: REAR END GEAR RATIO- A100

Post by hastingsman on Sun Jul 02, 2017 3:12 am

THANKS MUCH!
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slowflapper

Number of posts : 920
Location : GA
Age : 48
Registration date : 2010-07-29

Re: REAR END GEAR RATIO- A100

Post by slowflapper on Sat Jul 08, 2017 5:26 pm

The stock rear gear ration that came with your rig should be listed on the info plate riveted to the drivers side fender well beside the seat (mine says, 355 rear gearing on it).

There are some things to consider in adjusting your RPM, rear weel and tire size, manual vs auto trans, and rear gearing.

It's probably a 741 type rear chunk, there may or may not be a metal tag under one of the chunk bolts, mine didn't have a tag. The gear ration was stamped on the out edge of the ring gear and matched my info plate.

I got my van with 3:55 gears and 14" wheels with low profile tires (chicano low rider look), it was screaming at 55mph.

I swapped the rear gear to a 2:76 and left the 14" rims but went to a 235/70 tire, I have to run the gears out a little now before shifting but it pulls about 2200 at 65mph which is doable.

eta: There are some online calculators that figure gearing and rim/tire size to rpms/mph, thats a good start
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hastingsman

Number of posts : 68
Location : south of Grand Rapids, Mi.
Age : 66
Registration date : 2015-11-07

Re: REAR END GEAR RATIO- A100

Post by hastingsman on Sat Jul 08, 2017 5:50 pm

That's what I've been after, the rear end number it was born with. Thanks for pointing out Chrysler's willingness to share info on an easy to locate plate.

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