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02-18-2022, 12:27 PM | #1 |
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Join Date: May 2018
Location: Coral Springs, Florida
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Differential Gear Ratio
I'm having to replace my rear end, it's gear ration: 3:78. It's a '31 PicUp I dearly enjoy driving, live in a small South Fla. city. It's driven semi-daily. I'm considering going 3:54 don't want the 4:11 at all. I'd like some advise/experience from you guys. Altho traffic has gotten rude lately, my 3:78 could keep up
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02-18-2022, 12:46 PM | #2 |
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Location: Largo Florida
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Re: Differential Gear Ratio
There is about 4 mph difference between the different ring/pinions. A 3:25 [?] is about the same.
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02-18-2022, 03:56 PM | #3 |
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Re: Differential Gear Ratio
A pickup is a light weight A. The lower gear ratio should work great for around town. If you're going to start hauling grain and gravel, 4:11 would be the way to go.
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02-18-2022, 05:23 PM | #4 |
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Location: Melbourne, Australia
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Re: Differential Gear Ratio
The convention is that the lower ratio actually has a higher number the way it is expressed. 4.11 is a lower ratio than 3.78. That is, for the same engine revs, the speed is lower.
Last edited by Synchro909; 02-18-2022 at 06:02 PM. |
02-18-2022, 08:28 PM | #5 |
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Location: Bucks Co, Pa
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Re: Differential Gear Ratio
My Coupe needed a rear! Period! I had two choices, A) Buy a good used rear, or B) rebuild the old rear with a new gear set. I chose B. Rebuilding A differentials is something I never did before. First off, Get the new gear set I chose 3.54 with bearings etc, about $700. This coupe is not a daily driver and the whole project took about 2 months. Best thing I ever did! Better Gas mileage, a lot quieter, but the rear surprise was the better hill climbing. I have a hill nearby and the old rear couldn't make it better than 35 (Traffic was usually about 50 mph)with the new rear, I make it at 40/45. The 3.54 seemed to unlock the power (torque) of the engine. The only mod is a bored out manifold with B carburetor. I heartily recommend you do this.
Terry |
02-18-2022, 08:48 PM | #6 |
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Re: Differential Gear Ratio
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02-19-2022, 07:30 AM | #7 |
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Location: Western North Carolina
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Re: Differential Gear Ratio
I would think that the 3.54 would be adequate for Florida where there are no mountains to climb. It also depends on your engine. How is the torque? Is the engine a strong runner?
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02-19-2022, 09:54 PM | #8 |
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Join Date: May 2010
Location: Bucks Co, Pa
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Re: Differential Gear Ratio
My advice! Find Tom Endy's site on rears and use it for a guide. It details all the little stuff you will need to complete the job. Also I recommend you purchase a laser thermometer/heat gun so you can monitor the heat rise of the parts once the car is back up and running again. they're hand when doing a brake job too. In fact, they can be a wonderful diagnostic tool that every mechanic should have in his box. For engines, radiators, transmissions , wheel, and rear ends. Good luck!
Terry |
02-20-2022, 08:25 AM | #9 |
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Re: Differential Gear Ratio
Here is a performance chart for various gear ratios:
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02-20-2022, 09:39 AM | #10 |
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Location: Coral Springs, Florida
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Re: Differential Gear Ratio
Bob.
Now I didn't know about the 3.70. I assumed, by rotating my rear tire in gear, with the hand crank that I was 3.78. I'm keeping your placard on my phone Thanks Everyone |
02-20-2022, 10:30 AM | #11 | |
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Join Date: Jul 2015
Location: SouthWest Michigan
Posts: 363
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Re: Differential Gear Ratio
Quote:
Not knowing what you have for a motor but ,i can tell you i have a 3:25 gear and would not want anything lower, if they made a 3;00 gear i would go with that now it is your car your choice Terry |
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02-20-2022, 12:06 PM | #12 |
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Re: Differential Gear Ratio
rfitzpatrick, I think that the 3.70:1 gears were aftermarket when the Model A was new. I do not know if any exist today.
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02-20-2022, 12:14 PM | #13 |
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Re: Differential Gear Ratio
Bob,
it might be helpful to show the tooth counts on the R&P for each ratio. J
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02-20-2022, 01:14 PM | #14 | |
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Re: Differential Gear Ratio
Quote:
http://www.santaanitaas.org/wp-conte...ing-Pinion.pdf Tom Endy |
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02-20-2022, 01:17 PM | #15 | |
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Re: Differential Gear Ratio
Quote:
http://www.santaanitaas.org/wp-conte...vised-2014.pdf Tom Endy |
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02-20-2022, 03:09 PM | #16 |
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Re: Differential Gear Ratio
Thanks Tom,
very helpful John
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