8.2 or 8.5 BOP? 1970 Skylark 350 from Peru

Discussion in 'Got gears?' started by César Machicao, Sep 18, 2022.

  1. Hey guys! greetings from South America, Perú!
    A 4 years ago a friend and I found a 1970 Skylark, original with 350 2bbl, TH350 and this rear end, eventually with a little research I realize that it's a BOP 8.2. but some people here suggested that it's a 8.5 BOP. Knowing that the option of upgrade the BOP 8.2 are limited I wonder if it's a BOP 8.5 in effect.

    I have plans to upgrade the engine with some ported head work, a little more aggressive camshaft that the original, adjustable pushrods, probably bigger head valves, 4bbl intake and Quadrajet (my objetive it's produce an amount of 300 to 350 hp and a respectable number of pound feet of torque as well), 4 speed M20 and I'm thinking in a 3.23 final ratio with sure grip.


    Pictures of the rear end before and after the sandblasting process of the frame.

    Currently with the car in a local body shop there's no chance to know the casting number of this unit, but in your experience and knowledge Is this a 8.2 or 8.5 BOP?


    In a extended article about GM rear end guide I found this picture as a 8.5 BOP, and in another GM site some people say "That is a BOP 8.2 reared. The corporate 8.5 has little ears off the bottom on each side"

    If is a 8.2, What are my real options for build this particular unit with 3.23 final ratio with sure grip?
    Fabcraft Metalworks is not longer producing this unique setup for this rear end, Is there any member of the community specialized in rear units or company that you can suggest me for the accurate parts that I'm looking for? I talk with West Coast Differentials a few months ago and they suggest me that with a new internal carrier inside of the BOP 8.2 will be enough for solve my problem, Is this true?

    I should mention that in this areas there's no more chances to find a 8.5 GM rear end from another 68-72 GM A body, and also the 12 bolts units are extremely rare. Also there's not an option installing a 9 inch Ford. I just can find a GM 8.2 rear end from a 1965 Biscayne, much wide than a A Body.

    Hope that I can receive your accurate suggestions about my project.
    Thanks a lot!
    Dano likes this.
  2. I will glad if you can provide me the correct casting numbers for a 8.5 BOP unit and 8.2 as well, so I will check it when the body car is ready
    Dano likes this.
  3. LARRY70GS

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

    Those little ears are the ID for an 8.5. The 8.5 also uses two brackets and 4 cap screws to attach the rear U joint to the yoke. The 8.2 uses two U bolts and 4 nuts to attach the u-joint to the yoke. It is probably the 8.2, the 8.5 was in the 1971-2 A bodies. You don't need casting numbers to ID this rear, just look at it.
  4. Bens99gtp

    Bens99gtp Well-Known Member

    By the photos its an 8.2
  5. BrianTrick

    BrianTrick Brian Trick

    The rearend that is in the chassis is 68-70 Buick 8.2”. There are currently ZERO gearsets available for that.
    The rearend on the floor jack is an 8.5”. Plenty of parts available for that.
  6. monzaz

    monzaz Jim

    Please can we call it a 8.25 ... We have to some how make this rear DIFFERENT than the 8.2 early Buick which takes the same parts as a Pontiac rear 8.2
    1968 1969 1970 ...lets call them 8.25 as they are more heavy duty than the 8.2 early Buick rears.
    You can find better gears ...IF you can find a skylark sport wagon (which is a good chance of having a 3.23 ratio) or of course a GS

    The rear in the chassis will have a 724 last three digits or a 700 last three digits in the casting number found on the passenger side of the center cast iron center the same side you install fluid in the rear.
    The rear is NOT a bad rear ...actually a very good designed rear...Only issue is NOT aftermarket support on parts.
    If your drive shaft is a 2 piece...One that slides into another...best to change that out with a different one... Dry rott of the rubber I am sure has already set in and will cause vibration and or out of phase driveshaft if it separates.
    If you do switch from 8.25 (existing rear) to 8.5 (the one on the floor jack) you will need to get a short drive shaft anyway. Pinion shaft on a 10 bolt 8.5 corp rear is slightly longer and the 8.25 shaft will not fit between the trans and the rear end yoke length anymore.

    JD Race
    Dano likes this.
  7. BrianTrick

    BrianTrick Brian Trick

    We could call it an 8.3”. That should make it different.
  8. monzaz

    monzaz Jim

    I know but I think that would really weird people out. LOL.
    sean Buick 76 likes this.
  9. I really appreciate your kindness Larry, Ben Brian and Jim in the observation of this particular piece, I realize that my unit doesn't have the lower lugs on the bottom of the center section characteristic of the 8.5 units. By the way, I took the image of the 8.5 unit from a website of GM rear end guide, not mine.

    Jim, Is there any chance to find the 3.23 (or similar) gearset and a POSI traction unit for the 8.25 rear end even in used but decent condition? Discard the fact of extremely rare chance to find a Sport Wagon Skylark or even a GS in these areas.

    Apart from that, and the incredible luck to find an 8.5 rear unit here from a 68-70 Gm A Body in the immediate future, I only have the option of an 8.2 GM rear unit from a 1965 Biscayne, wider than a a A body, with the possibility to rebuild this piece like a A body unit, with the couple top mounts and the other suspension brackets, new axles and drum brakes.


    I believe there are many parts available for this unit (8.2 GM) but I don't know if it's worth it.
    Thanks a lot for the information.
  10. LARRY70GS

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

  11. LARRY70GS

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

  12. That would be terrific Larry, unfortunately I talked with owner and manager of the company Fabcraft (Dave) by phone a couple weeks ago and he mentioned that currently he's not be able to produce this particular Sure Grip unit and the gearset as well. At this point my only option with this rear end is asking for used parts but in good shape, or waiting for an NOS gearset and POSI of Brian or Jim for this particular setup.

    If it's not possible, I'll have to build a rear unit with the 8.2 GM from the Biscayne, cutting the tubes and adding new axles, without counting with the bracket mount suspension that it will be add, hope that for this particular unit there are aftermarket options for Sure Grip carriers and gearsets as well.

    Thanks a lot
  13. BrianTrick

    BrianTrick Brian Trick

    I still make posi units for them,but not a lot of demand without gearsets. I’ve just been adding them to the existing 2:73,2:93,3:23 rearends to make them a posi.
  14. Bens99gtp

    Bens99gtp Well-Known Member

    Wondet what it cost to have a 8.5 shipped down
  15. Bens99gtp

    Bens99gtp Well-Known Member

    Sometume just saving up and doing it right is better than forcing something to fit
  16. monzaz

    monzaz Jim

    There was a guy on the other posi looking to sell his 3.23 posi 8.25 rear. MAybe he would just part out the gears and posi unit for you and send it?? Maybe?
    1971 1972 are the year skylark cutlass and i have seen them in Lemans too in rare cases..?? all built at the same plant in 1972 they just shoved rears under cars to get rid of them as the next gen car platform was totally different and the rears would not work in those 1973- 1977 chassis
  17. monzaz

    monzaz Jim

    The Impala rear will not fit your a body does not have the correct mounting...Just wasting time and energy on that one. 65-70 impala ONLY
  18. monzaz

    monzaz Jim

  19. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    I wonder if the 8.5 made it into any of the Holden stuff.

    Edit- sorry, I'm on about 8 minutes of sleep. For some reason i thought the OP was in Australia... I'm still curious about that though.
  20. Thank you so much Brian an Jim for your awesome responds, hope that guy wants to sell the entire setup and the possibility to send it to a friend in the East Coast, the international shipment would be another hurdle but with some luck I will not have to build some Frankenstein rear unit or transplant from another rare car.

    Thanks a lot!

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