8 3/4 rear end worn out or not?

Transmission and Drivetrain Tech

  1. 7duce swinger

    7duce swinger Well-Known Member

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    So i did a thread about my rear end a while back, but i am still puzzled. I had thought my 8 3/4 was an open rear end, because it would only leave one mark (tire mark that is), but now it leaves two from a stop. Could it have been the 318 before didnt have enough power to spin both? Now i have a holley 650 vac secondaries, headers, and thumper cam with 360 heads @ 60 cc's. Before it would spin one tire, now it leaves two good dark marks, i was gonna buy another centersection with suregrip unit, but i do not want to spend the money if i dont have too. Could it be that its worn or does it need more power to spin both? Im just thinking about why it would only spin one tire. Oh and i drove it on the street today and it spun one tire again, is it at certain rpms that it catches? A certain speed? Or is it supposed to do it at all times? Please help me out on this, so that i do not have to buy another case. Thanks alot fabo members.
     
  2. 67valiant 100

    67valiant 100 go fast or go home

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    Jack the rear up, put car in neutral (with e-brake off), spin one wheel if the other wheel on the other side spins the same direction you have a sure grip or some other traction device. If it spins the other way you have an open rear.
     
  3. 7duce swinger

    7duce swinger Well-Known Member

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    Yeah i have done that already, although tires spin in opposite directions, when the rear is jacked up. Thats why i am puzzled if its worn out or not. My driveway n street have proof marks.(not other car tiremarks) street has new blacktop. When i hold the brake, n give it a little gas, then release the brake it leaves two marks. So is it some other type of "traction device" or is it jus a worn out sg unit? I was told it was out of a 72 charger when i bought the car.. Its a 489 case, from wheel to wheel its 52 inches( inside of wheels) if it helps any.. They spin in opposite directions, when lifted off the ground, but they leave two marks not only one, so what does everybody think is going on? Thanks for any replies..
     
  4. cosgig

    cosgig MoBro Inc. FABO Gold Member

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    Yea, it could be a worn out SG unit, and if it's originally from a 72 Charger it would be the cone style Auburn unit. When the side of the cone wears out from contact with the side of the housing, the cone bottoms out...no contact with the side, no SG!!!

    This can be repaired by machining the bottom of the cone and adding the amount of removed material in shims on the top of the cone to maintain the required thickness, but if the housing is scored you will be looking for a replacement unit. It is imperative that you investigate this immedietly to prevent further damage to the housing if you plan to continue using this unit.

    Removing the center section of the 8 3/4" is really easy, and I would think about doing so soon to inspect the SG and to verify just what it is you have here!! Take a pic and post it here for verification if you're unsure of what you have when you get it opened up. Wern't you unsure of it's ratio also?? You can also check the ring gear for verification of the ratio while it's open also!! And, it being a 489, now would be a good time to add the hard spacer in place of the crush sleeve if you're planning on rebuilding this unit!!

    Good luck and keep us posted!! Geof
     
  5. 7duce swinger

    7duce swinger Well-Known Member

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    Thanks for the help guys.. So to remove the case, i have to remove the five bolts on each side then pull the axles out how far exactly?? Then take the housing will come down with ease right? thanks for the help, how much am i looking into machining the cones, or to rebuild this unit?
     
  6. 5.7 hemi

    5.7 hemi FABO Gold Member FABO Gold Member

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    You can take them all the way out or use a jack stand to support the axle so it doesn't rest on the inner seal and just pull it far enoug to get the center out. If you have the clutch style sg, then get a new set of clutches, soak them in the additive, mark the case halves and undo the bolts that hold the halves together (they are left hand thread), pull apart the halves starting with the non ring gear side and keep the clutches in order as you pull them out, the the 4 pinion spider set up, then the other clutches. New clutches should come with instructions (follow them to the t), keep the inner splines aligned as best as you can, (easy way to do this is to stand 1 axles on it's studs and slide everything on that axle, now lay it on the ground, do the other side the same way) now slide both case halves together matching up your "mark" on the halves, and snug up the left hand bolts, make sure the axles slide in/out without any problem and torque to spec. Thats the long/short of it. Now reinstall everything, gasket, fluid, etc., do some figure 8's and enjoy the new found traction, or lack of, lol.
     
  7. 7duce swinger

    7duce swinger Well-Known Member

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    Thanks 5.7, so its the five bolts i have to undo right lol? So will i know how to spot if its worn out easily? Also where/what car can i remove the brake drums from so that i can change my bolt pattern?? My axles have 10 holes, right now theyre on 4 3/4 chevy bolt pattern ,( yes thats typed correctly), Im not crazy either. The axles have 4 1/2, and 4 3/4 bolt patterns, Like moser/yukon etc etc... But i need the drums for mopar pattern where can i score some? Thanks for any feedback
     
  8. 5.7 hemi

    5.7 hemi FABO Gold Member FABO Gold Member

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    The clutches are about 65-75 bucks depending on where ya get them. As far as getting brakes drums for an A body, I'm not sure, as I dont know alot about the A body interchange and so on. I'm sure someone will chime in and answer your questions.
     
  9. 7duce swinger

    7duce swinger Well-Known Member

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    Thanks, Is there a specific brand i should be getting or are they all the same? Where would i buy them from Jegs,summit etc. etc.?
     
  10. 5.7 hemi

    5.7 hemi FABO Gold Member FABO Gold Member

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    Dr. Diff has them along with Jegs, Summit and maybe the local Dodge dealer. They are all made by Dana Spicer.
     
  11. cosgig

    cosgig MoBro Inc. FABO Gold Member

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    Don't go out and buy a clutch pack until you verify that it is indeed a Clutch-Pak SG. I'm gonna bet that it's a 489 case with the cone style SG unit, if it was the original rear in the above mentioned Charger!! geof
     
  12. 7duce swinger

    7duce swinger Well-Known Member

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    Yeah thanks guys, first i need to find out first. I do know its a 489 case with 3.23 gears. I have to open it up to find out tho ill post what i find thanks!
     
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