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  1. #101
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    May 2003
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    I-95, Old exit #69 ;]
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    Default Re: 9 3/8" rear differences

    you have an open diff, here's the shadetree way to figure out what you've got:

    1 - set parking brake with engine off while car is parked on a level surface
    2 - chock the RF tire, front and rear
    3 - put car in Neutral
    4 - jack up LR tire and put a jackstand under the axle
    5 - take a piece of chalk / grease pencil / etc and mark a line on the rear of your driveshaft and on the inner sidewall of your LR tire
    6 - laying under the car, use your hand to rotate the LR tire
    7 - count how many times the driveshaft rotates for one rotation of the tire
    8 - divide by 2


    figuring out a limited slip is much the same except you have to jack up both rear tires at the same time and you eliminate step 8.

  2. #102
    Join Date
    Feb 2002
    Location
    SW Ohio
    Posts
    400

    Default Re: 9 3/8" rear differences

    Bob,
    With an open diff, you have to multiply the driveshaft revolutions by 2 instead of dividing, if you're only turning one tire. Or, turn the one tire exactly twice and count driveshaft revolutions directly. I've found a few decent gears in the junkyard this way when I couldn't get both sides jacked up. It's actually easier than trying to turn both sides of an open diff exactly one time.

    Dave
    David Powell
    76 LeSabre 2dr 455 12.54@107
    76 LeSabre 4dr ht 455 14.50@93
    73 Riviera 455
    83 Regal 455 11.70@116

  3. #103
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    May 2003
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    I-95, Old exit #69 ;]
    Posts
    5,308

    Default Re: 9 3/8" rear differences

    eh, i sometimes forget which direction i'm multiplying.

    thanks for the catch.

  4. #104
    Join Date
    Feb 2002
    Location
    SW Ohio
    Posts
    400

    Default Re: 9 3/8" rear differences

    No prob, it happens to everyone. Great way to find good gears at the yard. Just because it's not posi doesn't mean the gear won't be decent. Found many open 7.5" diffs that had 3.42, 3.73 and even 4.10 gears in S10 trucks back when I was into Monzas.

    David
    David Powell
    76 LeSabre 2dr 455 12.54@107
    76 LeSabre 4dr ht 455 14.50@93
    73 Riviera 455
    83 Regal 455 11.70@116

  5. #105
    Join Date
    Jun 2010
    Location
    OTR...out of Dallas for now...
    Posts
    59

    Default Re: 9 3/8" rear differences

    So the '72 LeSabre/350 used an 8.5" rear, correct? One of the posts in this thread mentioned using parts from the Auburn posi in a '96 LT1 Caprice. My question: would the complete rear end "rotor-to-rotor" from a '96 9C1 fit under my LeSabre (rear disc brakes would be cool ) or should I just put a posi and lower gears (200-4R swap planned) in my current rear?
    John
    1972 LeSabre base 4-door sedan SOLD 14 Jun 2011 :(
    1972 LeSabre Custom hardtop ON LAYAWAY :)

  6. #106
    Join Date
    Sep 2004
    Location
    Michigan, USA
    Posts
    15,250

    Default Re: 9 3/8" rear differences

    Quote Originally Posted by 72LSRydah View Post
    So the '72 LeSabre/350 used an 8.5" rear, correct? One of the posts in this thread mentioned using parts from the Auburn posi in a '96 LT1 Caprice. My question: would the complete rear end "rotor-to-rotor" from a '96 9C1 fit under my LeSabre (rear disc brakes would be cool ) or should I just put a posi and lower gears (200-4R swap planned) in my current rear?
    Your best bet is to start a new topic with the questions. You'll not get much feedback here since the the big car rear ends are what's being covered.

    Devon
    Fuel & Brake Systems Engineer
    "I can live with doubt and uncertainty and not knowing. I think it's much more interesting to live not knowing than to have answers which might be wrong." - Feynman
    "Good data is precious. The problem I have is when some damned fool fails to use it properly." - Slingerland

  7. #107
    Join Date
    Feb 2002
    Location
    Elyria, OH
    Posts
    2,282

    Question Re: 9 3/8" rear differences

    where can I get replacement clutch packs and those auburn preload springs for the 9-3/8......


    Mark....
    Mark passed away on February 14, 2017. Please remember him as a car and gun nut with a heart of gold.



    69 GS 400 stage1,4 speed,3.64 posi
    72 Skylark w/70 455 stg.1,BB trans,3.64 posi
    72 Riviera w/factory sunroof, 3.42 posi
    68 Olds Ramrod 350 4 speed, 3.91 antispin
    73 Cutlass S W-31 350,TH 400, 3.73 antispin

  8. #108
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    Sep 2004
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    Michigan, USA
    Posts
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    Default Re: 9 3/8" rear differences

    Quote Originally Posted by MGSCP View Post
    where can I get replacement clutch packs and those auburn preload springs for the 9-3/8
    Contact Jim a.k.a. "monzaz".

    http://www.v8buick.com/member.php?u=3880

    Devon
    Fuel & Brake Systems Engineer
    "I can live with doubt and uncertainty and not knowing. I think it's much more interesting to live not knowing than to have answers which might be wrong." - Feynman
    "Good data is precious. The problem I have is when some damned fool fails to use it properly." - Slingerland

  9. #109
    Join Date
    Aug 2003
    Location
    wisconsin
    Posts
    183

    Default Re: 9 3/8" rear differences

    I don't think their available anymore? Those 9 3/8 clutches pretty much never wear out from what I have seen.
    grandville464
    2010- 11.64 E.T- Best Mph 115.07- 60ft 1.63
    2011- 11.501 E.T 117.74 MPH 1.62 60 ft- 4550 pds

  10. #110
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    Sep 2004
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    Michigan, USA
    Posts
    15,250

    Default Re: 9 3/8" rear differences

    Jim has other parts that do the job.

    Devon
    Fuel & Brake Systems Engineer
    "I can live with doubt and uncertainty and not knowing. I think it's much more interesting to live not knowing than to have answers which might be wrong." - Feynman
    "Good data is precious. The problem I have is when some damned fool fails to use it properly." - Slingerland

  11. #111
    Join Date
    Aug 2003
    Location
    wisconsin
    Posts
    183

    Default Re: 9 3/8" rear differences

    Quote Originally Posted by DaWildcat View Post
    Jim has other parts that do the job.

    Devon
    Ah Good info.
    I just recently found out that fab craft is making gears for the full size rears, Like The MP series in the grandville in only 3.55 ratio's.. I have my original rear with a different posi I got for it a few years ago, But I don't know if the carrier is for that deep so not sure what would need to be done to it.
    grandville464
    2010- 11.64 E.T- Best Mph 115.07- 60ft 1.63
    2011- 11.501 E.T 117.74 MPH 1.62 60 ft- 4550 pds

  12. #112
    Join Date
    Feb 2010
    Location
    Framingham, Ma
    Posts
    2,784

    Default Re: 9 3/8" rear differences

    Quote Originally Posted by grandville455 View Post
    Ah Good info.
    I just recently found out that fab craft is making gears for the full size rears, Like The MP series in the grandville in only 3.55 ratio's.. I have my original rear with a different posi I got for it a few years ago, But I don't know if the carrier is for that deep so not sure what would need to be done to it.
    I'd double check that

    1965-1976 Full Size Pontiac / Olds / Buick / Chevy ring & pinion in 3.55 ratio

    Seems like they may be another company that's lumping everything together as "GM 12 bolt"
    "To achieve great things, two things are needed: a plan, and not quite enough time."
    --Leonard Bernstein

  13. #113
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    Feb 2002
    Location
    Elyria, OH
    Posts
    2,282

    Question Re: 9 3/8" rear differences

    Quote Originally Posted by bammax View Post
    I'd double check that

    1965-1976 Full Size Pontiac / Olds / Buick / Chevy ring & pinion in 3.55 ratio

    Seems like they may be another company that's lumping everything together as "GM 12 bolt"
    would that be the 8.7/8 full size rear end.....and is it the same diff that is used in the Chevelle 12 bolts....
    Mark passed away on February 14, 2017. Please remember him as a car and gun nut with a heart of gold.



    69 GS 400 stage1,4 speed,3.64 posi
    72 Skylark w/70 455 stg.1,BB trans,3.64 posi
    72 Riviera w/factory sunroof, 3.42 posi
    68 Olds Ramrod 350 4 speed, 3.91 antispin
    73 Cutlass S W-31 350,TH 400, 3.73 antispin

  14. #114
    Join Date
    Aug 2003
    Location
    wisconsin
    Posts
    183

    Default Re: 9 3/8" rear differences

    Quote Originally Posted by MGSCP View Post
    would that be the 8.7/8 full size rear end.....and is it the same diff that is used in the Chevelle 12 bolts....
    I honestly don't know? Just something I was told by a friend of mine.The Mp Is a 8 7/8, but it uses a 31 spline axle where the gm 12 bolts use only a 30.. I guess it may be best to call them?
    grandville464
    2010- 11.64 E.T- Best Mph 115.07- 60ft 1.63
    2011- 11.501 E.T 117.74 MPH 1.62 60 ft- 4550 pds

  15. #115
    Join Date
    Feb 2002
    Location
    Da 'Nawlins Bayous.....
    Posts
    5,042

    Default Re: 9 3/8" rear differences

    Quote Originally Posted by DaWildcat View Post
    First you need to know exactly what you want, because believe it or not, knowing you want a posi carrier isn't enough info. You first need to find out what your current rear axle gear ratio is.

    If you have a 2.78:1 or 3.07:1 gearset, you need a posi carrier from a 1967-1970 Wildcat, Electra or Riviera that also carries 2.78:1 or 3.07:1. If your Riv currently has a 3.42:1 or 3.91:1 gearset, you'll have to find a posi carrier that had those ratios instead.

    In other words, you can't run a set of 3.07:1 gears on a carrier built to handle 3.42:1 & up. Make sense?

    Next, when you know which carrier you need, post in Parts Wanted.

    Then wait.

    Then buy one when it shows itself.

    Then take the car with your new carrier to a good shop that can set it up with your old gears. It's not necessarily a job for a novice.

    Devon
    Thread revival!!!!!!! I am confused now. (Doesn't take much)

    I have a set of 3.07s and a 3.42 posis that were supposed to go in the '66 Riv. That car is no more. I am just about to buy a 2.93 because it came out of a '73 GS Riv for my '71.Do I have it correct that I can use the others in my '71?

    Cruisin' the Coast is around the corner and I'm tired of hearing I could never spin them if it had to turn two.
    [/SIGPIC]
    Jason -friends call me (J)-POP

    B.P.G. #1500
    R.O.A. # 8427


    MY (nearly) DAILY DRIVER --'71 Rivvy Black and Gold.

    '85 Regal triple gold 40k mi.
    Love your country, fear your government, drink more beer
    I pledge allegiance, not blind obedience!!!!
    You can't trust a man who never curses

  16. #116
    Join Date
    Sep 2004
    Location
    Michigan, USA
    Posts
    15,250

    Default Re: 9 3/8" rear differences

    Quote Originally Posted by Poppaluv View Post
    Thread revival!!!!!!! I am confused now. (Doesn't take much)

    I have a set of 3.07s and a 3.42 posis that were supposed to go in the '66 Riv. That car is no more. I am just about to buy a 2.93 because it came out of a '73 GS Riv for my '71.Do I have it correct that I can use the others in my '71?

    Cruisin' the Coast is around the corner and I'm tired of hearing I could never spin them if it had to turn two.
    No, the early carriers will not work in your '71. You need to find 1971-1975 donors for that.

    Devon
    Fuel & Brake Systems Engineer
    "I can live with doubt and uncertainty and not knowing. I think it's much more interesting to live not knowing than to have answers which might be wrong." - Feynman
    "Good data is precious. The problem I have is when some damned fool fails to use it properly." - Slingerland

  17. #117
    Join Date
    Feb 2002
    Location
    Da 'Nawlins Bayous.....
    Posts
    5,042

    Default Re: 9 3/8" rear differences

    Quote Originally Posted by DaWildcat View Post
    No, the early carriers will not work in your '71. You need to find 1971-1975 donors for that.

    Devon
    So,can i use the '71 posi carrier to hold the '66 gears?
    [/SIGPIC]
    Jason -friends call me (J)-POP

    B.P.G. #1500
    R.O.A. # 8427


    MY (nearly) DAILY DRIVER --'71 Rivvy Black and Gold.

    '85 Regal triple gold 40k mi.
    Love your country, fear your government, drink more beer
    I pledge allegiance, not blind obedience!!!!
    You can't trust a man who never curses

  18. #118
    Join Date
    Sep 2004
    Location
    Michigan, USA
    Posts
    15,250

    Default Re: 9 3/8" rear differences

    That I do not know.

    Devon
    Fuel & Brake Systems Engineer
    "I can live with doubt and uncertainty and not knowing. I think it's much more interesting to live not knowing than to have answers which might be wrong." - Feynman
    "Good data is precious. The problem I have is when some damned fool fails to use it properly." - Slingerland

  19. #119
    Join Date
    Feb 2002
    Location
    Da 'Nawlins Bayous.....
    Posts
    5,042

    Default Re: 9 3/8" rear differences

    Quote Originally Posted by DaWildcat View Post
    That I do not know.

    Devon
    Quoted for just the rarity.
    [/SIGPIC]
    Jason -friends call me (J)-POP

    B.P.G. #1500
    R.O.A. # 8427


    MY (nearly) DAILY DRIVER --'71 Rivvy Black and Gold.

    '85 Regal triple gold 40k mi.
    Love your country, fear your government, drink more beer
    I pledge allegiance, not blind obedience!!!!
    You can't trust a man who never curses

  20. #120
    Join Date
    Jan 2014
    Location
    Huron, SD
    Posts
    197

    Default Re: 9 3/8" rear differences

    So heres a question are the control arm mounting points on a 1970 9 3/8 the same as an A-body? obviously the axle is wider but could this bolt in my 65 GS? I have a 70 lesabre 455 with the 9 3/8 and i think its a posi, the car is getting junked after i pull the motor so it would be a free bullet proof rear. any thoughts?

  21. #121
    Join Date
    Sep 2012
    Location
    MI.
    Posts
    2,921

    Default Re: 9 3/8" rear differences

    Quote Originally Posted by sodak65 View Post
    So heres a question are the control arm mounting points on a 1970 9 3/8 the same as an A-body? obviously the axle is wider but could this bolt in my 65 GS? I have a 70 lesabre 455 with the 9 3/8 and i think its a posi, the car is getting junked after i pull the motor so it would be a free bullet proof rear. any thoughts?
    Not only is it wider,it doesn't have the "ears" on the "pig" that the upper control arms attach to like the A-body does on your '65 GS.

    You may be able to sell the 9 3/8 or parts from it though.GL

    Derek
    64 Skylark,401 Nailhead,ST400,3.23:1Posi
    64 Skylark,305Vortec sbc,700R4,12blt Posi 3.73,low 14s. A sbb 300 stroker planned for it.
    72 Skylark Convert. in progress, Not yet assembled 455 .020 over,70 heads with stage1 valves,gasket matched and bowl blended,transmission to be determined.
    65 Chevy Impala,4,400lbs,383sbc,700R4,3.07posi,1.80 60' foot time low 13s @101mph,15mpg city,24mpg highway

  22. #122
    Join Date
    Jan 2014
    Location
    Huron, SD
    Posts
    197

    Default Re: 9 3/8" rear differences

    thats a bummer I guess i should have crawled under the car in the snow to look but its -10 out lol. I was looking at picstures of these rears online and it showed up mounts just like my GS maybe differnt year? what does the Lesabre use for upper mounts then?

  23. #123
    Join Date
    Oct 2014
    Posts
    5

    Default Re: 9 3/8" rear differences

    Quote Originally Posted by SharpSabre455 View Post
    Chris:

    I agree with Tom T. I found mine in a yard and it took a LONG time. Finding parts for these cars is not as easy as finding parts for a Lark or GS. You just have to keep looking.

    Paul
    I got a 1970 buick wildcat convertible and I can't find rear end gears and/or posi. Can anyone help me out here? Trying to finish this before winter comes around. Thanks

  24. #124
    Join Date
    Sep 2012
    Location
    MI.
    Posts
    2,921

    Default Re: 9 3/8" rear differences

    Quote Originally Posted by obiestar23 View Post
    I got a 1970 buick wildcat convertible and I can't find rear end gears and/or posi. Can anyone help me out here? Trying to finish this before winter comes around. Thanks

    Contact monzaz in the rears and gears section.GL


    Derek
    64 Skylark,401 Nailhead,ST400,3.23:1Posi
    64 Skylark,305Vortec sbc,700R4,12blt Posi 3.73,low 14s. A sbb 300 stroker planned for it.
    72 Skylark Convert. in progress, Not yet assembled 455 .020 over,70 heads with stage1 valves,gasket matched and bowl blended,transmission to be determined.
    65 Chevy Impala,4,400lbs,383sbc,700R4,3.07posi,1.80 60' foot time low 13s @101mph,15mpg city,24mpg highway

  25. #125
    Join Date
    Jan 2015
    Posts
    5

    Default Re: 9 3/8" rear differences

    Ok I just read this whole thread here is what gathered from it and also what i can add to help.

    Here's what I know from experience.

    The Oldsmobile built 12 bolt 9 3/8" can be only found in 71-75 Buick's and Oldsmobiles. Sedan housings and station wagon housings are different due to the sedan being coil suspension and wagons being leaf.

    Axle shafts are a non c-clip bolt in style with 31 spline. Wagon and sedan are the same length.

    Pinion yokes and driveshafts are different between wagon and sedan but are swappable. Also a GM 8.5 yoke from 71-76 will work.

    Cadillac housings are totally different the upper control arms are a different design and the center section is offset. But the driveshaft yoke and lower control arms are the same.

    There is absolutely no aftermarket support for these rear ends to my knowledge.

    My questions to you guys are..

    is 3:42 the lowest possible gear set for 71-75?

    is 3:42 the lowest gear set for 66-70?

    Any aftermarket support for 66-70 gears?


    What type of mods does a guy need to do to use an older 66-70 gear set in a 71-75 housing? Besides the older seal?

    Does anyone know if a modified 9 3/8 spool will work?


    Thanks

 

 
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