rear end question!

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    Author Topic: rear end question!  (Read 3528 times)

    Offline Mr. 6pak2go

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    rear end question!
    « on: May 10, 2006 - 10:42:03 PM »
    Iv got a question about an 8 3/4 rear! one how do i identify what i have i know i have an 8 3/4 rear but how can i identify if its a 489 or a 741?? its the original rear my car is a 72 barracuda 318 3 speed!! if that helps! and two whats the difference in the two??   thanks Kevin!
    « Last Edit: May 10, 2006 - 10:47:17 PM by Mr. 6pak2go »
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    Offline Killer_Mopar

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    Re: rear end question!
    « Reply #1 on: May 10, 2006 - 11:31:28 PM »
    To find out if its a 741 or a 489, just look at the casting number on the lower-drivers side of the 3rd member (below the u-joint)...should be pretty easy to find. The major difference between the two is that the 489 uses a crush sleeve. You really dont have to worry about the strength, because all the 8 3/4s are pretty damn strong.
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    Offline Chryco Psycho

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    Re: rear end question!
    « Reply #2 on: May 11, 2006 - 02:04:32 AM »
    The 741 is the smallest with a 1 3/8" pinion , the 742 was the strongest with a 1 3/4" pinion & the 489 was larger but can be more prone to failure due to the crush sleeve , not size , the 489 was a tapered pinion with a max diameter of 1 7/8"
     They are all strong as mentioned & basically will not fail as long a sthe tires spin , with good traction all of them will fail ,I have proof
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    Offline Carlwalski

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    Re: rear end question!
    « Reply #3 on: May 11, 2006 - 02:09:35 AM »
    Quote from: Chryco Psycho on May 11, 2006 - 02:04:32 AM

     They are all strong as mentioned & basically will not fail as long a sthe tires spin , with good traction all of them will fail ,I have proof

    Is this in real world street driving or track? (copious amounts of hp)
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    Offline Chryco Psycho

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    Re: rear end question!
    « Reply #4 on: May 11, 2006 - 02:23:07 AM »
    both , I could easily lift the front wheels on the street with my Duster on street tires , lots of shock load , 4 spd definatly help explode them,
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    Offline Carlwalski

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    Re: rear end question!
    « Reply #5 on: May 11, 2006 - 02:34:48 AM »


    4-speed would definitely help, but with, say my car 400hp 3.91 gears it should last a while eh....
    Or are you saying all 8-3/4 cars will blow up eventually.  :grinno:
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    Offline tactransman

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    Re: rear end question!
    « Reply #6 on: May 11, 2006 - 07:03:06 AM »
    You can convert the crush sleeve to a solid spacer with shims to get the benifits of the 1 7/8 pinion and a solid spacer.  Plus it is reusable!!!!!  :cheers:  here is a link
    http://www.jegs.com/webapp/wcs/stores/servlet/CategoryDisplay?lang=-1&catalogId=10002&storeId=10001&categoryId=13621
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    Terry-tactransman 
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    Offline 1BADFISH™

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    Re: rear end question!
    « Reply #7 on: May 11, 2006 - 07:12:12 AM »
    My car has an open rear end and if I were to look for a good set of gears, what is easiest to find, or what should I look for? I'd like 3:23 or 3:55 gears. Any sellers?  :bigsmile:
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    Offline ShelbyDogg

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    Re: rear end question!
    « Reply #8 on: May 11, 2006 - 07:27:37 AM »
    Mr6Pack, Since you have a '72 you probably have a 489 case. BUT if you didn't buy the car new, I've been known to install the weaker 741 cases into cars that I've sold. You have to get under there and look at the numbers.


    1BADFISH, Unless you buy a set from a friend that has a new Pig already setup with a newer set of gears, I would buy a new set.  There are lots of old gears out there that are worn out and whine.  You can always just get a limited slip or new style detroit locker and just add it to your rear end.  That way you get a posi and don't have to pull out the pinion.

    Tactransman, have you used that spacer?  Do you know why the sleeve with shims is a cheaper price?
    836-04-0013-1  Chrysler 8.75” 489  $32.99   
    836-04-0013-S  Chrysler 8.75” 489 w/shims  $25.99
     
    Rob
    « Last Edit: May 11, 2006 - 07:43:32 AM by shelbydogg »
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    Rob

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    Offline zerfetzen

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    Re: rear end question!
    « Reply #9 on: May 11, 2006 - 11:01:20 AM »
    I know some bracket racing guys who push about 500-550hp from their 440 Cuda, and they say they've never torn up a 742, but have torn up many 489's.  So it seems like 742's are stronger, though I don't know if that's with the tougher shim and spacer in the 489 or not.  Does anybody know at about what hp you'd want to switch over to a Dana 60?  And I'm just assuming that a Dana 60 is the kind of rear end you'll only buy once and have for life, regardless of how you drive on it...unless you hit top fuel or something crazy.

    Assuming good traction, how much power can these 8 3/4's take before the switch must be made to a Dana 60?  Thanks.
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    Offline Chryco Psycho

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    Re: rear end question!
    « Reply #10 on: May 11, 2006 - 11:37:25 AM »
    the solid spacer is the fix for the 489 & no I am not saying that all 8 3/4 diffs will eventually fail , in most cases you will never have a problem with one
     the Dana wil take a lot more abuse / power
     What an 8 3/4 will take is variable , automatics do not hit the diff as hard & traction is a variable , a 4 spd at 500 hp with excellent traction will definatly hurt a 8 3/4 , I distroyed 3 in my duster running mid 11 seconds & the one in my Cuda didin`t last 1 pass with te same engine but I was using a 4 link & 14 x 32  Eagle slicks too 
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    Offline tactransman

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    Re: rear end question!
    « Reply #11 on: May 11, 2006 - 07:17:56 PM »
    Quote from: shelbydogg on May 11, 2006 - 07:27:37 AM
    Tactransman, have you used that spacer?  Do you know why the sleeve with shims is a cheaper price?
    836-04-0013-1  Chrysler 8.75” 489  $32.99   
    836-04-0013-S  Chrysler 8.75” 489 w/shims  $25.99
     
    Rob
    Yes It is in my 8 3/4 for my Challenger.The only thing I can think of is they sell more of the ones with the shims ( because you have to have shims) so the price is cheaper   :dunno:
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    Terry-tactransman 
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    Offline ShelbyDogg

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    Re: rear end question!
    « Reply #12 on: May 11, 2006 - 07:24:30 PM »
    Thanks Terry.

    Zerf, about the 742s or 489s, they don't break at the pinion, they break at the pinion to ring gear contact point. My 8-3/4 tore it's ring gear teeth off! Ford 9" rear ends have a better contact angle so all of the Pro-stock racers use them. When my stock axles were twisting so much that they were getting dangerous, I put a dana in it and didn't have to touch it ever again.
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    Rob

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    Offline tactransman

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    Re: rear end question!
    « Reply #13 on: May 11, 2006 - 07:25:32 PM »
    I raced a 1970 Duster with a 600 - 650 HP 440 that left with about 2 feet of air under the front tires.It had a 8 3/4 with a spool - 4.86 gears -automatic - no transbrake , that ran for 2 1/2 years with no failures. But it was a lighter car (3000 lbs.)
    « Last Edit: May 12, 2006 - 11:42:27 AM by tactransman »
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    Terry-tactransman 
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    Offline tactransman

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    Re: rear end question!
    « Reply #14 on: May 11, 2006 - 07:28:28 PM »
    Quote from: shelbydogg on May 11, 2006 - 07:24:30 PM
    Thanks Terry.

    Zerf, about the 742s or 489s, they don't break at the pinion, they break at the pinion to ring gear contact point. My 8-3/4 tore it's ring gear teeth off! Ford 9" rear ends have a better contact angle so all of the Pro-stock racers use them. When my stock axles were twisting so much that they were getting dangerous, I put a dana in it and didn't have to touch it ever again.
    A Ford 9 " also has a pilot bearing at the end of the pinion gear , that has to be a good set up
     ( help keep the teeth from pushing apart) :thumbsup:
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    Terry-tactransman 
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