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Old 10-17-2019, 06:23 PM   #1
lalkie
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Default Model AA High Speed Rear Axel

Is there a difference between the Model A rear axle under a 29 Pickup and a 1930 31 Model AA. The ad indicates it is a 31 ford high speed rear differential for a model a truck. Not sure if I know the difference. I have a note to the person to get more information. Thanks Larry
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Old 10-17-2019, 06:44 PM   #2
Truckerjim
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Default Re: Model AA High Speed Rear Axel

The 29 should be a worm gear rear end and the 31 should be a ring and pinion set up. The 29 might be a fast rear end than the 31.Jim
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Old 10-17-2019, 07:49 PM   #3
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Default Re: Model AA High Speed Rear Axel

I’m pretty sure the 5.14 set was only available on the mid 30 to 31 models.
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Old 10-17-2019, 08:36 PM   #4
Purdy Swoft
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Default Re: Model AA High Speed Rear Axel

I think that the 28-29 high speed worm gear ratio was 5.17
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Old 10-17-2019, 09:01 PM   #5
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Default Re: Model AA High Speed Rear Axel

There is a world of difference between the rear axle for a '29 pickup and a '30-31 AA rear axle. The '29 and spring arrangement is functionally the same as a standard Model A, the AA rear has side mounted springs that look like they can support the space shuttle, and overall a bigger build to carry the rated loads.
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Old 10-18-2019, 12:37 AM   #6
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Default Re: Model AA High Speed Rear Axel

Here is a link to the aafords rear axel info page. Model A and Model AA rear ends are very different.

https://aafords.com/aa-chassis/aa-4000-rear-axle/
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Old 10-18-2019, 12:37 AM   #7
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Default Re: Model AA High Speed Rear Axel

deleted. double post
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Old 10-18-2019, 11:46 AM   #8
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Default Re: Model AA High Speed Rear Axel

Of course there is a large difference in the AA truck rear axel and the rear axle used in cars and light trucks , They don't interchange .
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Old 10-18-2019, 03:49 PM   #9
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Default Re: Model AA High Speed Rear Axel

Quote:
Originally Posted by Purdy Swoft View Post
Of course there is a large difference in the AA truck rear axel and the rear axle used in cars and light trucks , They don't interchange .

Even though the transmissions SORT OF do. Many Model A were fitted with the Borg Warner 4 speed simply to get a power take-off for various onboard and off-board uses.

It is a big heavy clunker of a transmission.

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Old 10-18-2019, 04:00 PM   #10
Purdy Swoft
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Default Re: Model AA High Speed Rear Axel

The 28-29 AA trucks used the worm gear style backends .I believe that the high speed ratio was 5.17

I agree with modeleh on post number three ,

5.14 was the ratio for the later spiral bevel backends used on the mid 30 through 31 AA trucks

Most model A pickups on the passenger car chassis used the 3.78 standard ratio .

I think that a 4.11 ratio gear was also available

Some have said that the 4.11 gear was only for special order
I think that a 4.11 ratio was also available
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Old 10-27-2019, 06:33 PM   #11
lalkie
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Default Re: Model AA High Speed Rear Axel

I am sorry for waiting so long for the input. From the pictures it looks like the brake drums are a lot wider than on my pickup. I was not able to see any spring mount. The rear end is listed on westlopecraigslist in grand junction co for $100.00. Mr rear axle is making noise when i let off the gas. I thought the price was reasonable. I appreciate the help. If anyone needs me to look at the axle let me know and i can contact the seller. thanks Larry
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Old 10-27-2019, 06:58 PM   #12
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Default Re: Model AA High Speed Rear Axel

You may find a Model A rear end in the $100 range. Usually a "set aside" for various reasons which may include making noise when the driver let off the gas. (A common sign of rear-end gear issues usually connected with pinion.) Most $100 rear ends DON'T come with any sort of guarantee except maybe "worked the last time I used it."

What exactly constitutes "worked?"

Your best plan of attack might be to source a reasonable looking set of used gears - examining your present gears will probably give you a clue of what NOT to look for.

Many with strong engines and pursuing more "roadability" in this modern automotive world are upgrading from 3.78 gears to perhaps 3.54 gears (higher top end -slower take-off from a stop) or even the more expensive 3.27 gears. So there are 3.78 gears around of reasonable condition at a reasonable price. You will be doing a setup of a rear end (technically a challenge but not overwhelming - more common sense) so that will be your time to decide on an upgrade (at about $200 difference)

Its a good winter project. Working evenings with parts in hand and assuming you don't find further problems to correct maybe a week total?

Best online instruction is Tom Endy's instruction found at https://www.santaanitaas.org/tom-endys-tech-articles/ There are many articles but the main one might be https://www.santaanitaas.org/tom-endys-tech-articles/

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Old 10-27-2019, 08:38 PM   #13
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Default Re: Model AA High Speed Rear Axel

Yes that is a high speed AA rear axle. https://westslope.craigslist.org/pts...998462074.html
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Old 10-27-2019, 09:07 PM   #14
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Default Re: Model AA High Speed Rear Axel

$100.00 is a great price. But shipping that whole rear end is going to be killer.
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