9 3/8" rear differences

Discussion in 'A boatload of fun' started by quicksabre, Apr 22, 2005.

  1. bob k. mando

    bob k. mando Guest

    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. quicksabre

    quicksabre Well-Known Member

    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.

  3. bob k. mando

    bob k. mando Guest

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

    thanks for the catch.
  4. quicksabre

    quicksabre Well-Known Member

    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.

  5. 72LSRydah

    72LSRydah Well-Known Member

    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 :grin: ) or should I just put a posi and lower gears (200-4R swap planned) in my current rear?
  6. DaWildcat

    DaWildcat Platinum Level Contributor

    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.

  7. MGSCP

    MGSCP Guest

    :Do No: :puzzled: where can I get replacement clutch packs and those auburn preload springs for the 9-3/8......:puzzled: :Do No:

  8. DaWildcat

    DaWildcat Platinum Level Contributor

  9. grandville455

    grandville455 Well-Known Member

    I don't think their available anymore? Those 9 3/8 clutches pretty much never wear out from what I have seen.
  10. DaWildcat

    DaWildcat Platinum Level Contributor

    Jim has other parts that do the job.

  11. grandville455

    grandville455 Well-Known Member

    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.
  12. bammax

    bammax Well-Known Member

    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"
  13. MGSCP

    MGSCP Guest

    :Do No: 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....:puzzled: :puzzled: :puzzled:
  14. grandville455

    grandville455 Well-Known Member

    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?
  15. Poppaluv

    Poppaluv I CALL WINNERS!!!

    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.:rolleyes:
  16. DaWildcat

    DaWildcat Platinum Level Contributor

    No, the early carriers will not work in your '71. You need to find 1971-1975 donors for that.

  17. Poppaluv

    Poppaluv I CALL WINNERS!!!

    So,can i use the '71 posi carrier to hold the '66 gears?
  18. DaWildcat

    DaWildcat Platinum Level Contributor

    That I do not know.

  19. Poppaluv

    Poppaluv I CALL WINNERS!!!

    Quoted for just the rarity. :eek2: :)
    OldDrummer55 likes this.
  20. sodak65

    sodak65 Well-Known Member

    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?

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