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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
----------------
Attachments Rear Axle_Parts Manual.JPG (35KB - 18 downloads)
Attachments Rear Axle_8.25 Casting.JPG (38KB - 18 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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Location: NorCal
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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