Buick 8.5 rear

Discussion in 'Got gears?' started by V6sleeper, Jan 5, 2023.

  1. V6sleeper

    V6sleeper Well-Known Member

    Hey Buick buddy's, im about to drop in a fresh 455 in my 70 sportwagon, it has a one year newer 71 8.5 10 bolt buick rear in it im not too familiar with the buick 8.5 only know about the Gn 8.5 and Gm 12 bolt.
    My question is will it hold the power without any issues or is there anything i should be aware of doing to strengthening it up, it is a posi, not sure of the gear ratios in 71 , the motor dynod at 550hp/575tq at 5300rpm...
    Thanks in advance!
    Dano likes this.
  2. LARRY70GS

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

    The 71-72 8.5 center section and guts are identical to the GN rear, except that it is bolt in axle, the GN is C clip. It's a really great rear. I have a 1971 8.5 in my 70 GS. When I swapped it in, I upgraded to 30 spline Moser axles with a matching Eaton Posi carrier, 3.73 Yukon gears, and a TA Performance girdled cover. I think the stock 28 spline rear is up to the task unless you plan to do a lot of racing with sticky tires.
    Oldskewl59, FLGS400 and V6sleeper like this.
  3. V6sleeper

    V6sleeper Well-Known Member

    Thanks Larry, do you know what stock gearing it could possibly have? im not planning on track racing it a lot maybe a few passes at Atco and some spirited driving around Long Island.. i drove the car for months with the SP code 350 in it and the gears didnt feel too low of a ratio so im thinking 290-308's possibly if that sounds accurate?
  4. Mart

    Mart Gold level member

    Lift wheels off ground by jack under rear, in neutral, put a grease crayon mark on driveshaft, turn wheel 1 turn and count revolutions of driveshaft.
    3 turns and a bit = 3.08 etc.
  5. LARRY70GS

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

    Look for the axle code. Here's the 1971 page from the Chassis Manual.

    Probably 3.08, about 2400 RPM at 60 MPH.
    V6sleeper likes this.
  6. Bens99gtp

    Bens99gtp Well-Known Member

    I ran very high 10s on stk axles on my 8.5. I wouldn't tell anyone else too but they are strong

    Here is when i said its time to upgrade

    But not sure the 30 spline Moser's are going to cut it either for me. Pic 2 is Moser axles with 50 passes

    Attached Files:

    69GS430/TKX and V6sleeper like this.
  7. BrianTrick

    BrianTrick Brian Trick

    The 8.5” is one of the best rears ever built. In stock form,it can go 11:80’s before stressing the shafts. Upgrade to 30-spline shafts and a good unit,and it will take plenty of abuse.
    V6sleeper likes this.
  8. bignastyGS

    bignastyGS Maggot pilot

    Mine is similar to Larry's build except the ratio in mine is 3.90.I'm going to throw over 900 rwhp at it with the supercharged motor I have. I had mine built by Jim M (monzaz) a few years ago. The only issue I had was the one rear wheel bearing gave it up after many 1/4 mile shots and 3-400 miles of street driving on it. I managed to replace the "new" bearings that were Chinesium with some NOS original bearings..No more issues now.They are a stout rearend as well.
  9. monzaz

    monzaz Jim

    Biggest problem we have with the 8.5 bolt in axle rears. Those crappy A9 tapered bearings. HAVE to find NON TAPERED bearings from somewhere Chinese or non Chinese. straight barrel bearings are the ticket. The seals are too narrow to keep a tapered bearing in its race properly.... with a straight barrel type bearing end play will not be an issue as there will be no up down axle play because the seal is not pressed against the bearing enough.
    69GS430/TKX likes this.
  10. monzaz

    monzaz Jim

    ANother reason axles twist is cool down time. If you hot lap your car and it does not have a chance to cool parts back down the twisting will happen on parts like that.
    I AM NOT saying that could never happen with the way the world is now...lol. BUT this is a good way to help keep a check on that.
    more than three hits in a row in the hot summer it will be very hot for the components.
    We see this at the blue suede cruise in Norwalk track...lol. Cars go round and round and round cause many do not want to go but some just keep hitting laps as fast as they can and then you will see some finally break something...lol.
  11. BrianTrick

    BrianTrick Brian Trick

    I have noticed the seals that I have received in the last 4 months are nice and wide again. So far so good. Another option is to find the older straight roller replacements. I have been finding some older Bowers before they cheaped-out.
  12. monzaz

    monzaz Jim

    .470 is not good enough....020 in turns just keeps pounding the seal - .490 no one makes them anywhere. Yes you can keep trying to find old stock...but eventually it will run out. I have been buying them your buying them...It will end.
  13. monzaz

    monzaz Jim

    I found some old SEALED bearing A9 on a few ebay sales. They have 'o' rings and is one big wide bearing NO seal separate...lol. ALL kinds of designs out there if you really hunt.
  14. sean Buick 76

    sean Buick 76 Buick Nut

    If one of you guys has some good seals that you can sell please message me. Mine are fine but I want to buy some for the future.

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