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Identify Mopar 8 1/4 rear axle
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jboymechanic
Posted 2019-05-23 10:03 AM (#582452)
Subject: Identify Mopar 8 1/4 rear axle



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Early Mopar 8 1/4 axles were used, as I know, in 6 cylinder cars in the Forward Look Era (and beyond). They are a banjo or Hotchkiss design just like a Mopar 8 3/4 or Ford 9 inch differential. So if you were in a junk yard or in some other situation where you couldn't remove the diff and measure the ring gear diameter, how would you identify the rear axle as a 8 1/4 versus a 8 3/4? I know the early 8 3/4 had a casting number that ends in "657" (similar to later ones having 741, 741 or 489), but what would a 8 1/4 have? How about mounting studs? 8 3/4 has 10 studs, how many does the 8 1/4 have? Any other unique features to look for to ID the early 8 1/4 rear diffs?

Thanks.
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Powerflite
Posted 2019-05-23 10:54 AM (#582453 - in reply to #582452)
Subject: Re: Identify Mopar 8 1/4 rear axle



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My '56 Plymouth 8 1/4 rear end had a fill plug in the back of it. I assume that it was required because there wasn't a fill plug cast into the pig. I'm not sure if later ones have that or not.


Edited by Powerflite 2019-05-23 9:43 PM
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57chizler
Posted 2019-05-23 3:20 PM (#582461 - in reply to #582452)
Subject: RE: Identify Mopar 8 1/4 rear axle



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The pre-'62 8 1/4" housing has a casting number that ends in 448 and has 11 attaching studs/nuts.
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jboymechanic
Posted 2019-05-24 10:37 AM (#582490 - in reply to #582452)
Subject: Re: Identify Mopar 8 1/4 rear axle



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Perfect, thank you!
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westaus29
Posted 2019-05-26 6:43 AM (#582532 - in reply to #582490)
Subject: Re: Identify Mopar 8 1/4 rear axle


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My Detroit built '55 Plymouth Belvedere Suburban V8 diff is banjo style and I believe 8 1/4. It has 11 studs, but casting number ends in 544 (casting marking A 1141544 10-11-55 B) and ratio is 3.9. I have concluded it is a substitute from an Aussie Plymouth, which retained the earlier 53-54 design, confirmed by checking a couple of junkyard chassis. So there may be earlier diffs which are similar to 55/56.

I am trying to figure out how to change to original 3,54 ratio and 11 inch brakes, as per original and am keen to learn more. It has been suggested I look for a later back axle but those are pretty rare in Oz .. only one I have seen in 12 months looking was $1500, a bit beyond my budget. The problem is the parts book has part numbers but the diff carrier only has a casting number. I have ordered a 53-54 parts list CD to try and learn more.
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Space Trukin Wagon
Posted 2019-05-27 9:07 AM (#582557 - in reply to #582461)
Subject: RE: Identify Mopar 8 1/4 rear axle



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57chizler - 2019-05-23 3:20 PM

The pre-'62 8 1/4" housing has a casting number that ends in 448 and has 11 attaching studs/nuts.


The 11 -vs- 10 mounting studs to ID the difference between the 8-1/4 and 8-3/4 is excellent info. This has been confirmed on two axles that I have.
In addition the factory parts manual calls out the casting numbers as way to ID the axles when servicing / ordering parts.

See attached photo from 1960 parts manual. The last line in the "Notes" section it states casting:
> 1828488 is 8-1/4
> 1820657 is 8-3/4

Also when confirming the casting numbers on the rear carrier section the 8-1/4 embossed number is located between the two ribs on the drivers side. Wheres the 8-3/4 embossed number was located as expected on the lower edge of the rear carrier which is also the same location for later 741, 742 and 489 8-3/4 carriers.

- Photo attached showing the location of part number on the 8-1/4

Edited by Space Trukin Wagon 2019-05-27 9:09 AM




(Rear Axle_Parts Manual.JPG)



(Rear Axle_8.25 Casting.JPG)



Attachments
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Attachments Rear Axle_Parts Manual.JPG (35KB - 373 downloads)
Attachments Rear Axle_8.25 Casting.JPG (38KB - 325 downloads)
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westaus29
Posted 2019-05-28 8:55 PM (#582635 - in reply to #582557)
Subject: Re: Identify Mopar 8 1/4 rear axle


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That info on the casting numbers, in particular the last three digits, helps make sense of some of the other discussion Ive read on diffs.
The 55-59 parts manuals dont mention casting numbers, and I had never looked at the 60 parts manual even tho its on the same cd. Learning all the time!

There is also info about what diffs go in what mopar on the interchange manual on http://www.mymopar.com/index.php?pid=107
I am still trying to figure out how to interpret it.
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57chizler
Posted 2019-05-29 12:46 PM (#582657 - in reply to #582635)
Subject: Re: Identify Mopar 8 1/4 rear axle



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Regarding the casting number; from my experience, the casting number is often one digit off from the part number. The part number for the '58-'61 8 1/4" housing is 1828447 which coincides with 1828448 being the casting number.
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imp610
Posted 2021-02-03 8:12 AM (#608495 - in reply to #582452)
Subject: Re: Identify Mopar 8 1/4 rear axle



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Great to find this discussion! Found out that we have a 8 1/4 axle in our 1960 Belvedere, was planning to replace the pinion seal, but before disassembly searching the web I canĀ“t find any info of is there a crush sleeve or a spacer between the pinion bearings?

Just to be sure before giving the pinion nut some force, has it to be marked versus the yoke and count revolutions out/in or just torque back in specs an then again how much would that be in ft.lbs?

Anybody done this?

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56D500boy
Posted 2021-02-03 11:53 AM (#608499 - in reply to #608495)
Subject: Re: Identify Mopar 8 1/4 rear axle



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I don't believe that there is a crush washer/sleeve in those 8.25" rear diffs (at least that is what I was told when I did my rear seal). Others with more experience will correct me if I am wrong

I think that your pinion ("yoke") seal will be PN 1738831 which crosses to Timken 5126

https://mibearings.com/index.php?main_page=product_info&products_id=...

https://www.motionindustries.com/products/sku/01314480

Torque on the nut is 250 lb-ft.





(1960RearDiff_1.jpg)



(1960RearDiff_2.jpg)



Attachments
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Attachments 1960RearDiff_1.jpg (141KB - 339 downloads)
Attachments 1960RearDiff_2.jpg (179KB - 209 downloads)
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Powerflite
Posted 2021-02-03 12:01 PM (#608500 - in reply to #582452)
Subject: Re: Identify Mopar 8 1/4 rear axle



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Crush sleeves is a newer technology that didn't come out until later. I just put non-crush sleeve yolks on TITE with my large air gun.

Edited by Powerflite 2021-02-03 12:04 PM
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imp610
Posted 2021-02-03 12:30 PM (#608502 - in reply to #582452)
Subject: Re: Identify Mopar 8 1/4 rear axle



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Great news! I have a National #5126 inhand to install. Just removed the nut and yoke, man that was tight... Reguired a 4 feet long bar and my son to step on, and he ways about 150 pounds! How much is the torque to tighten the nut? Is it the same as with the 8 3/4 rear end? Been reading from various sources 210 or 240 lbs?
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56D500boy
Posted 2021-02-03 1:00 PM (#608505 - in reply to #608502)
Subject: Re: Identify Mopar 8 1/4 rear axle



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imp610 - 2021-02-03 9:30 AM
Great news! I have a National #5126 inhand to install. Just removed the nut and yoke, man that was tight... Reguired a 4 feet long bar and my son to step on, and he ways about 150 pounds! How much is the torque to tighten the nut? Is it the same as with the 8 3/4 rear end? Been reading from various sources 210 or 240 lbs?


I guess that you didn't believe me when I said 250 lb-ft.

Okay, I lied.

The manual says 240 lb-ft (min).




Edited by 56D500boy 2021-02-03 1:02 PM




(1960RearDiff_3.jpg)



Attachments
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Attachments 1960RearDiff_3.jpg (85KB - 200 downloads)
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imp610
Posted 2021-02-03 1:36 PM (#608507 - in reply to #582452)
Subject: Re: Identify Mopar 8 1/4 rear axle



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Ok so 240 ft. lbs it is

Edited by imp610 2021-02-04 2:39 AM
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