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Technical GM REAR END

Discussion in 'The Hokey Ass Message Board' started by M8250, Sep 12, 2014.

  1. M8250
    Joined: Sep 23, 2010
    Posts: 37

    M8250
    Member

    I just purchased a 1961 impala SS and i can only find the cast number on the rear end.....
    E221 8725880. Seller not talking. The car had sat for a long time and the positraction seems locked up and i need to know what i am working with. Yes, changed the oil and added the additive.
    If there is no other markings..... what year did Gm stop marking the hog head???? Thanks
    [email protected] Mason
     
  2. Hnstray
    Joined: Aug 23, 2009
    Posts: 12,355

    Hnstray
    ALLIANCE MEMBER
    from Quincy, IL

    1964 for full size Chevys was the last year for removable third member (hogshead).

    Ray
     
  3. M8250
    Joined: Sep 23, 2010
    Posts: 37

    M8250
    Member

    Would i be safe in assuming that since there is nothing but the casting number......that what is in my '61 is not a '61 rear end????? Thanks for your help. Mason
     
  4. aaggie
    Joined: Nov 21, 2009
    Posts: 2,530

    aaggie
    Member

    '55-'64 are interchangeable center sections.
     

  5. Wingom8250,

    I'm afraid I'm a bit confused... You mention being able to find the casting number (and what appears to be the date code) on your diff. Sounds like you are looking for something else on it, but what you are looking for it not clear to me? Can you elaborate on what you are trying to find?

    Scott/Gotta56forme
     
  6. saltflats
    Joined: Aug 14, 2007
    Posts: 12,594

    saltflats
    Member
    from Missouri

    If its a factory locker it will have a large letter P on the drivers front side.
    I would not be surprised that if you pulled it out you would find it has been welded up.
     
    WDobos likes this.
  7. models916
    Joined: Apr 19, 2012
    Posts: 379

    models916
    Member

    What makes you think it's an SS? Did you pay $50,000 for it? 61 SS is one rare bird. I want to see this thing. Pretty easy to pull the rear center out.
     
  8. "61 SS is one rare bird"..

    Sure was. I believe the SS in '61 was just a trim option in '61. You could get a 6 cylinder with a powerglide that year..with SS trim.
     
  9. M8250
    Joined: Sep 23, 2010
    Posts: 37

    M8250
    Member

    If there is "NO" factory info on the side of the hog head except for the "casting" information.... can i then assume the rear end in this 1961 Impala is not what came from the factory in 1961. Mason
     
  10. M8250
    Joined: Sep 23, 2010
    Posts: 37

    M8250
    Member

    According to GM spec's it has everything on it that was offered from the factory. Been stored since 1969.
     
  11. M8250
    Joined: Sep 23, 2010
    Posts: 37

    M8250
    Member

    This was the last SS produced the second week of August 1961.
     
  12. Wingom8250,

    In no particular order...

    That may be the original rearend, since the date code is E221:
    E: May
    22: 22nd
    1: 1961

    There may be other information on the outer perimeter of the diff(bolt circle) that will decode it further. It will be embossed by a striking stamps into the mental, IIRC. They are hard to see. Have a look at this at this link for decoding those letters/numbers:

    http://www.348-409.com/differential.html

    Also, after searching, I'm thinking your casting number may actually be 3725880, not 8725880, as I did find one link for 3725880. Lighting, eyesight, and grease/dirt, etc can lead to easily misreading the casting number, particularly 3's & 8's. etc. The more common casting number is 3725899. I think. I don't know much more about casting numbers.

    Lastly, I'm to understand the diff from the factory came with a metal tag on one of the diff bolts that would say something more about the diff information. They had different shapes that could correspond to the gear ratio. Unfortunately, these were often discarded when a diff may have been serviced, repaired or replaced. I've seen info on the tags, shapes, etc in the past, but am not finding anything today.

    I hate to send you offsite, but there is a guy on Chevytalk.com who has been rebuilding those era diffs for over 40 years. He knows this stuff like the back of his hand. His username there is DZAuto. You might try contacting him or doing a search on his past posts. Most everything I know (little) comes from info he has written.

    Good Luck,

    Scott/Gotta56forme
     
    loudbang likes this.
  13. mgtstumpy
    Joined: Jul 20, 2006
    Posts: 9,214

    mgtstumpy
    Member

    Definably a rare car if original as Chevy built only 453 x Impala SS's in 1961, 142 were 409. Rear axles were 3.36:1 with mandatory four-speed transmission. $50K seems about right. The axles code will be metal stamped on the axle tube adjacent to the carrier. Metal stamp on left rear axle tube on the rear side, letters and numerals 3/16 in. high, 3 in. outboard of carrier. http://www.oldride.com/library/1961_chevrolet_impala.html
     
  14. M8250
    Joined: Sep 23, 2010
    Posts: 37

    M8250
    Member

    You are super.... thanks to everybody that responded......Mason
     
  15. M8250
    Joined: Sep 23, 2010
    Posts: 37

    M8250
    Member

    Also.... air cond, power brakes, power steering, padded dash, tach, 4-speed, ect ect.
     
  16. That car if all original, deserves a nut and bolt rotisserie restoration, and put in a museum. It's a piece of history that needs to be seen by many and shared with the masses, due to the rarity. I've never seen a "true" '61 SS impala.

    If it was a clone, id drive the doors off it!!
     
    Last edited: Sep 12, 2014
  17. M8250
    Joined: Sep 23, 2010
    Posts: 37

    M8250
    Member

    I plan on having fun with it!!!! Mason
     
  18. hot rust
    Joined: Sep 18, 2007
    Posts: 779

    hot rust
    Member

    c'mon, no pics yet? inquiring eyes wanna see.....
     
    loudbang likes this.
  19. M8250
    Joined: Sep 23, 2010
    Posts: 37

    M8250
    Member

     
  20. M8250
    Joined: Sep 23, 2010
    Posts: 37

    M8250
    Member

    I have tried to upload a picture 3 times with no luck..... Mason
     
    31Vicky with a hemi likes this.
  21. M8250
    Joined: Sep 23, 2010
    Posts: 37

    M8250
    Member

    You might be able to help me ....on my cowl plate under ACC the following codes appear
    SS L C AC E I have searched and searched...nothing for my '61 Impala. Mason
     
  22. WDobos
    Joined: Jan 7, 2007
    Posts: 234

    WDobos
    Member

    Having had Chevrolets with the style of rear end you have in yours all my life(I'm 65) if there is no "P" on the third member it is NOT a posi rear end,just an open single traction rear end.
     
  23. M8250
    Joined: Sep 23, 2010
    Posts: 37

    M8250
    Member

     
  24. M8250
    Joined: Sep 23, 2010
    Posts: 37

    M8250
    Member

    Even though ..jacked up...both wheels turn in the same direction.... we think something is welded together. i will just get a "real" 3.08 positraction and install that goes with the original car. Thanks
     
  25. cavman
    Joined: Mar 23, 2005
    Posts: 669

    cavman
    Member

    I'd love to see a pic of it. An old friend of mine bought one new. He heated the springs to lower it, shaved all emblems except for the trunk "V", and drove the (beat) the crap out of it. It was just another car back then.
     
  26. M8250
    Joined: Sep 23, 2010
    Posts: 37

    M8250
    Member

     
  27. M8250
    Joined: Sep 23, 2010
    Posts: 37

    M8250
    Member

    "IF" i knew how to post a picture on this site......I would!!!! If you know how... give me your e-mail address i i will send a picture to you for posting. Mason [email protected]
     
  28. loudbang
    Joined: Jul 23, 2013
    Posts: 40,276

    loudbang
    Member

    Posting this for WINGOM8250

    Nice ride one of my best friends back in the day had one like it in black

    IMG_0767[2].jpg
     
    Hotrodmyk likes this.
  29. That car is in a lot better shape than I gave it credit for at the beginning of the thread. I wasn't expecting a completely done car!
     
  30. models916
    Joined: Apr 19, 2012
    Posts: 379

    models916
    Member

    Minimum engine for the 61 SS was the 305 hp 348. 4sp or HD powerglide. PS PB padded dash and tach was standard.
     

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