Rear end identification help

Discussion in 'Got gears?' started by Groucho70, Oct 5, 2017.

  1. Groucho70

    Groucho70 1970 Work in progress

    I know I'm asking alot here but can some identify this rear end which was removed from a 1971 Grand Prix from these pics? I'm not too concerned about the gear ratio but I'm hoping it's an 8.5 and not a 8.2. I. I'm looking to build this and install in my 70 Skylark.
     

    Attached Files:

  2. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Looks like the yoke uses the bolts and straps, look at the rear pumpkin and look for the 2 lugs underneath on both sides. Can't see that with the angle of your picture. Is the track width the same for a 1971 Gran Prix? It was not an A body, 68-72 was a G body. Don't think it is a bolt in replacement.

    8.5axle3.jpg
     
  3. Groucho70

    Groucho70 1970 Work in progress

    Thanks Larry. Thank ll ask for a better photo but if it's not a direct fit I'll definitely walk away from it
     
  4. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Yeah, a 1971 Gran Prix is a much bigger car, not an A body like your 70 Skylark. I would think it is wider, or the upper and lower control arm angles are different.
     
  5. wkillgs

    wkillgs Gold Level Contributor

    Wikipedia says the GP and Monte Carlo used a stretched A body frame. Might have the same rear suspension as a Skylark, so don't rule it out.
    UMI rear control arm kits fit both the GS and GP, but that doesn't mean the width of the rear is the same.
    A Hollander interchange manual would tell you for sure what is interchangeable.
     
  6. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    Yes, rear suspension the same as A-bodies.

    The frame is the same as an A-body from behind the cowl ALL the way back to the rear bumper mounts.

    A junkyard in Pennsylvania use to make convertible A-body frames out of GP and MC frames because they are boxed in like A-body convertible frame. They do it by cutting off the front and welding on the correct A-body front frame so I would have to say that the rear end will fit on a Skylark of the same years.
     
  7. Jim Jones

    Jim Jones Wretched Excess

    My Hollander manual states the following:
    1970-72 Grand Prix w/10 bolt inspection cover. Fits Grand Prix '70-72.
    1970-72 Grand Prix w/12 bolt inspection cover. Fits Buick Special '70, Chevelle '68-72, GMC '71-72 Sprint, Grand Prix '70-72, Monte Carlo '70-72, Tempest '70-72.

    Why a 12 bolt would interchange but not a 10 bolt is beyond me. But the mere fact that the 12 bolt will interchange tells me the suspension mounting points are the same. Perhaps the pinion flange differed on the 10 bolt. Hollander also states the 10 bolt used in the 1970-72 Monte Carlo will fit the full compliment of GM A-body cars '70-72.
     
  8. BrianTrick

    BrianTrick Brian Trick

    That is an 8.5" 10-bolt. That is the same 8.5" 10-bolt found under 71-72 Skylark/GS.

    Build it.
     
  9. monzaz

    monzaz Jim

    ALL 1964-1972 A-body rears are interchangeable. 64-66 will be a 1/2" narrower on each side and the spring perch mounts could need a bit modifying as there are just flat perches where the spring just bolts the bottom pig tail to the flat perch with a cup and bolt system. The newer style is just as raised cup and the spring just sit on and around this raise cup.
    The 71 72 LARK and Cutlass 10 bolt has all the same mounting points BUT requires a drive shaft mod shortening because it has a longer pinion shaft than any other GM a-body rear from that era. 64-72.
    ALL other 10 and 12 bolts will interchange with nothing more than a u-joint swap BOP to Chev MOOG 372 part number.

    Hope this clears up the A-body rear deal.

    Frames. Monte frame IS NOT boxed. Only the Grand prix / Pontiac ones were. pretty sure they stretched the frasme under the cowl as the doors are way longer than a chevelle and the core support is out on the front frame horns too... HAs a 6 foot long hood remember.
    TRUST me on the MONTE CARLO info...THAT is what I use to restro. I have had TONS of them. regular c-channel frame like a chevelle. GP does have the boxed frame WHICH made them heavier cars too....
     
  10. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    Went though this about 13 years ago and did all the measurements before I bought the rear frame of a GP welded to the front frame of a Chevelle to make an A-body "convertible frame". I was told it was fixture welded and as far as I could see by cross measuring, front to back measuring and so on they did a very professional job of it.

    The rear sections of the GP frame ARE the same as the A-body frames, as far as just in front of the cowl being different that may only be for the A-body style cars and the front section of the GP frame may be further under the door where they connect?
     
  11. BrianTrick

    BrianTrick Brian Trick

    The rear sections are,but not the whole frame,like it sits. Same with the ElCamino. It will fit a 2-dr A-body,by shortening the straight sections behind the rear wheel
     
  12. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    That may be true with the El Camino but not with a GP or a MC, case in point would be that the deck lids are the same for the '70 to '72 MC, GP and Skylarks with probably being the same for the Olds, Chevy and Pontiac A-body cars as well.

    When I ordered a deck lid for my Skylark, the box said Monte Carlo/Chevelle on the box! Fits great though.
     
  13. BrianTrick

    BrianTrick Brian Trick

    The rear axles have the same geometry or mounting points.
     
  14. monzaz

    monzaz Jim

    All front suspension is the same rear ends are the same mount points Lots of similar stuff on the chassis. .... Reason Monte Carlos were so parted out as they always had Disc brakes and 12 bolt rears in 1972 even the 350 4 bbl cars got the 12 bolts in montes... they were throwing them under all of them as the next year all the rears would NOT fit chassis changed in 1973. I parted out and restored many montes and they had great options that could be used on other A-body GM cars...Power windows, locks dashes bucket seats center consoles ....and on...
     

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