Basic 8 3/4 question

News:

  • Home
  • Help
  • Chat
  • Login
  • Register

    • « previous next »
    Pages: [1]

    Author Topic: Basic 8 3/4 question  (Read 2089 times)

    Offline mjb765

    • Full Member
    • ***
    • Posts: 660
    Basic 8 3/4 question
    « on: June 25, 2010 - 09:55:02 PM »
    I see people who have 8 3/4 rears describe as a "741" or a "489" center. How can you tell the difference? I know this may seem like a dumb question, but I am just getting back into the hobby after about a 20 year break in Harley Davidson land......now I am splitting my time between my 71 R/T and the bikes.....
    Logged


    Offline 72cudamaan

    • Resident
    • *****
    • Posts: 3248
    Re: Basic 8 3/4 question
    « Reply #1 on: June 25, 2010 - 10:19:23 PM »
    The three digit number is the casting number. It is cast right into the diff housing. Most say either the 489 or 742 casting are the strongest.
    Logged
    If I cant fix it, it's broke
     
    Andy  (phukker whither)

    Offline mjb765

    • Full Member
    • ***
    • Posts: 660
    Re: Basic 8 3/4 question
    « Reply #2 on: June 25, 2010 - 10:20:20 PM »
    OK--I will look....is there a better one to have or are they both about the same strength?
    Logged

    Offline 72cudamaan

    • Resident
    • *****
    • Posts: 3248
    Re: Basic 8 3/4 question
    « Reply #3 on: June 25, 2010 - 10:27:48 PM »
    For most applications, either will usually work just fine. I just read a thread somewhere here that the 742 is a bit stronger, though the 489 is close and can be made a bit stronger with mods. If you are really concerned then you could always upgrade to a Dana 60.
    Logged
    If I cant fix it, it's broke
     
    Andy  (phukker whither)

    Offline mjb765

    • Full Member
    • ***
    • Posts: 660
    Re: Basic 8 3/4 question
    « Reply #4 on: June 25, 2010 - 10:40:07 PM »
    Not that concerned...just curious...

    Thanks for the info
    Logged

    Offline djwhog

    • Jr. Member
    • **
    • Posts: 232
    Re: Basic 8 3/4 question
    « Reply #5 on: June 26, 2010 - 08:49:40 AM »
    the 3 diffs all have diff pinion shaft sizes, the 489 is actually the largest and suppose to be stronger, than the taper on the other 2, but they are all good and what he said, you can build a 489 to be better as far as tuffness.

    Also there are 2 posi main types, cones and clutches, clutches again are preferred, cones are strong, but when worn not reallt service but can be modded and serviced.

    Logged

    Offline HP2

    • Resident
    • *****
    • Posts: 4478
    Re: Basic 8 3/4 question
    « Reply #6 on: June 26, 2010 - 11:22:01 AM »
    Most common castings are 657, 741, 742, and 489.

    The 657 and 741 are small 1.38 stem pinions. Which are actually close in size to some of the bigger chev and ford offerings. The 742 pinions are 1.75 in diameter. The desireable thing about all three of these castings is that they use washers to set pinion deth, therefore they can withstand huge amounts of shock loading ie. drag strip launches with high powered engines. 

    The 489 case has an even larger 1.875 diamter pinion, but typically uses a crush sleve to set depth. The only problem with that is the crush sleeve can crush and destroy the gears if subjected to repeated high shock load. There are solid spacers out there that can replace the crush sleeve and eliminate the problem but they ar enot commonly used.
    Logged

    Offline Changin Gears

    • Sr. Member
    • ****
    • Posts: 1011
    Re: Basic 8 3/4 question
    « Reply #7 on: June 26, 2010 - 11:38:55 AM »
    All these are plenty strong for street aplications.  The only strength problems I've ever had with an 8.75 is the spider gears/sure grip which is common to all of these.

    I ran a 741 with a 440/4-speed and slicks for years.
    Logged


    The goal never changes - Stop the 60' timer with your back tires

    Offline 1970 RT Challenger 1970

    • Full Member
    • ***
    • Posts: 774
    Re: Basic 8 3/4 question
    « Reply #8 on: June 26, 2010 - 01:14:22 PM »
    Quote from: 72cudamaan on June 25, 2010 - 10:19:23 PM
    The three digit number is the casting number. It is cast right into the diff housing. Most say either the 489 or 742 casting are the strongest.

    Is the casting number internal and you would have to take it apart to see it?
    Logged

    Offline Katfish

    • Resident
    • *****
    • Posts: 3733
    • 70 Challenger
    Re: Basic 8 3/4 question
    « Reply #9 on: June 26, 2010 - 01:21:25 PM »
    Logged

    Offline Chryco Psycho

    • Administrator
    • C-C.com Guru
    • *****
    • Posts: 36620
    • 70 Challenger R/T SE 70 tube Chassis Cuda now sold
    Re: Basic 8 3/4 question
    « Reply #10 on: June 27, 2010 - 02:54:58 AM »
    casting # is external & along the side of the pinion
    Logged

    Challenger - You`ll wish You Hadn`t

    Offline thedodgeboys

    • Resident
    • *****
    • Posts: 3633
    • ''Normal’s Overrated''
      • THE DODGE BOYS
    Re: Basic 8 3/4 question
    « Reply #11 on: June 27, 2010 - 09:41:21 AM »
    Quote from: Chryco Psycho on June 27, 2010 - 02:54:58 AM
    casting # is external & along the side of the pinion

    Drivers side
    Logged
    Go Fast & Have Fun...
    70 6.1 HEMI 6-speed Drop Top...

    Offline RusTy/SE

    • Sr. Resident
    • ******
    • Posts: 5456
    • Just havin' fun
    Re: Basic 8 3/4 question
    « Reply #12 on: June 27, 2010 - 08:28:30 PM »
    There are some pics of my 741 case in the link below. Thanks to Moparal that thread's subject now has a happy ending :)

    http://www.cuda-challenger.com/cc/index.php?topic=67724.0

     :cheers:

    Logged
    Russ
    2001 Durango     1B4HS
    1970 Challenger  JS29U
    Restoration thread: http://www.cuda-challenger.com/cc/index.php?topic=27173.0
    Member since December 13, 2002
    Pages: [1]
    « previous next »