Interchange Rear Ends X-body

Discussion in 'Got gears?' started by buickapollo455, Jan 9, 2005.

  1. buickapollo455

    buickapollo455 Well-Known Member

    Can anyone help with x body rear end help? Have a 73 one wheel wonder and have found a posi in a 79 skylark, It has a 2.56, will the differential interchange to the 8.5 73 car or can I install it a a direct swap from the 79? Torque, I have a 455 with a mild cam and 2000 stall, will this other 79 rear end handle the torque? Rear end guys please give me some advise, thankyou craig
     
  2. oPh

    oPh Well-Known Member

    Craig,

    Hello, all the '77-79 Skylarks I've ever ck'ed in Pick-N-Pulls & crusher yards had the 7.5 X-body rear. Basically referencing hundreds of these year Skylarks, as we pull the 8.5 X-body hgs or rears when can get them priced right. The 8.5 X-body rear was still avail in some '77-79 X-bodys, but are usually still found in a good % of these year Novas.

    To quicky see what X-body rear the '79 is, it's quickest to ck the axle tube diam. The 8.5 X-body axle tubes are 3" diam. On the 7.5 X-body axle tubes they are noticably smaller in diam, around 2.5" diam axle tubes.

    Personally, am not impressed with the strength any of the 7.5 rears. Though have built quite a few up for "cruiser" cars with good used factory cone type posis & new gears... just adding up the expense with a $125 used low ratio posi, one can easily put $650 in such a stock axle 7.5 build, & one really doesn't end up with something that strong, so money is better spent in an 8.5.

    Good luck, if the rear turns out to be an 7.5, can always sell it, or pull the posi & sell it.

    Roger
     
  3. GStage1

    GStage1 Always looking for parts!

    Roger,
    Just wondering about an idea. I have seen many of the Cadillac Sevilles, 77-79 with leaf spring rears w/disc brakes. Would those be a bolt-in to the X-body cars? They are 8.5" rears and I thought that would be a great/cheap way to add rear disc brakes.
     
  4. oPh

    oPh Well-Known Member

    George,
    Hello. Yes have pulled gobs of rear disc pieces off late '70's Sevilles & used them in rear disc swaps. They won't swap directly, so I just usually pull what I need. The 5 on 5 pattern used rear rotors don't do much good on 4 3/4 boltpattern car, & the '77-78 Seville disc calipers physically ride a little closer to the rim due to the design (extra girth) of the caliper. Have managed to get the '79 rear calipers to clear inside 14" factory disc brake wheels but they will not fit inside every 14" wheel.

    Need more info, feel free & shoot me a PM.

    Roger
     
  5. GStage1

    GStage1 Always looking for parts!

  6. GStage1

    GStage1 Always looking for parts!

    You want an axle housing from a 71-2 Cutlass/Skylark.
    The 8.5" posi you can remove from any 8.5" rear from 71-89
    GM car/truck/van.
     
  7. oPh

    oPh Well-Known Member

    George,
    All the '78 model- early 90's GM 1/2 ton trucks, Blazers, & half ton vans that had factory 8.5 posi's, these posi carriers were Gov-locks, not near as good a piece, as the corporate 8.5 car posi carriers.

    Not sure how many GM Gov Lock r/e's that you have seen the results of the carrier blowing up, but its not a pretty sight. Often times when a Gov-Loc blows, it will take out a cap, the cap mtg area, & the rear cover. For years, our local relatively latemodel pickup salvages were getting $1200-1400 for a used non ABS 8.5 pickup rear with 3.42's or 3.73's & a Gov-Loc. Not hard to build a same style core housing up with new Auburn or Eaton posi, & all other new internals... all for quite a bit less & have a guaranteed better quality stronger rearend. As a result, have built quite a few late 80's-90 Chevy posi pickup rear up off my own core housings, new carriers & gears, & occassionally with good used 30 spline 8.5 Auburn carriers out of SS Impallas. On damaged Gov-loc's they're good for little.

    Personally can't see using decent shape Gov-locks in anything. Any Gov-lock carriers I come up with today, I throw on e-Bay to get rid of them, & let someone else face the music. :Dou:

    Roger
     
  8. GStage1

    GStage1 Always looking for parts!

    I have heard horror stories of the gov-lock. Seen a few in the yards and they were still there when the carcass went into the crusher. If you saw my article I state to get the GM 410408 case for 3 series gear sets. I have found the 3 series with 3.08, 3.23 and 3.42 in full size wagons from 80-88. I recently found an eaton 30 spline in an 89 wagon which I sold on Ebay. I have found just a few of the 410408 in GM vans. I don't know how they got there but they were there. I tell everyone to avoid the gov-lock. I also tell them to use the 2 series w/spacer plate for a street car but not for a serious street terror or track car. Funny, found many Trans Ams from 78-81 with the 2.41-2.56 gears and a posi. WOW, what a performance machine! :laugh:

    Just a note, do you have a website? Don't see one in your signature.
     

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