9 3/8" rear differences

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

  1. 66BuickLeSabre

    66BuickLeSabre Well-Known Member

    Thanks for the respones guys...Guess I got some researching to do but I appreciated the start...

    Car is never on the highway, I think maybe once or twice in the 4 years Ive had it...just an in town car.
  2. fleetwood

    fleetwood Active Member

    there was a demo derby guy around here that was playing with a lathe and made a spool fit the 12 bolt might have been a ford 9 inch?
  3. EEE

    EEE Straight out of lo-cash!

    I thought it was time to poke a stick at the hornets nest again and add some confusion to the situation. I've taken two posi carriers from full size Olds cars, like Delta 88/98's which have been from the early 70's, like 72/73. The rear axles on these cars look very much like the rear axles on the big Buicks from 71-76 with the 9 3/8. Twelve bolts on the cover with twelve bolts on the ring gear. They also have axle shafts that slide out by removing four bolts behind the brakes, just like on the Buick. As you can see, there's a difference in the thickness of the ring gear, and there is also a difference in the carrier design, probably similar to the 2.73-3.23 / 3.42 variation on the Buicks. I don't have the pinion gears, so I don't know what the ratios were (I remember vaguely calculating a 3.08 on one of them). It's also interesting to see that the ring gears have such a similar amount of teeth on them. I'm not sure if they're the same as the Buick's, but it would be fun to find out. I will have to get a better picture from the side, so we can start looking for clues.. to be continued.
  4. jamyers

    jamyers 2 gallons of fun

    I'm pretty sure that the 9 3/8" axles were actually made by Olds, at least originally, then they became part of the BOP parts bin.

    I'll bet that those two carriers are different series for the different ratios, but otherwise are interchangeable.

    Why didn't you take the pinions as well? If one of those is a deep gearset, it's not much use without it.
  5. EEE

    EEE Straight out of lo-cash!

    I thought the carriers were all the same until I read the thread again, and I didn't think much of getting the gears (until now). I've got an open 3.42 axle laying here too, I'll have to see if one of the posi carriers match up to the open 3.42 carrier.
  6. bob k. mando

    bob k. mando Guest

    I've taken two posi carriers from full size Olds cars, like Delta 88/98's which have been from the early 70's, like 72/73.

    I'm pretty sure that the 9 3/8" axles were actually made by Olds

    yes. ALL of the 9 3/8" housings were made by Oldsmobile, regardless of which make you find the rear in.

    and all of the 8 7/8" rears are made by Pontiac although the entire axle assembly will bolt in, in place of a 9 3/8".
  7. EEE

    EEE Straight out of lo-cash!

    The confusion continues, but there is some light in the tunnel as to decipher the Olds/Buick relation in the 9 3/8 world. Here's a picture of the differentials I have laying around. As you can see on the top of each of the carriers there is a design difference.

    Carrier No.1 as seen from the left is the open 3.42 Buick 9 3/8 diff taken from a '72 Electra I believe it was. The carrier has the number 759 marked on the top of it. The ring gear has the following code: 41B12 GM PA119 2, of course 41/12 gives the ratio of 3.42.

    Carrier No.2 in the middle is an Olds 9 3/8 taken from a 71/72/73 Delta 88/98 which has number 761 marked on top of it. The ring gear has the following code: 42B13 GM DN227 1, of course 42/13 gives the ratio of 3.23. I guess I should have taken the whole axle :dollar: :Dou:

    Carrier No.3 to the right is an Olds 9 3/8 taken from a 71/72/73 Delta 88/98 which has number 760 marked on top of it. The ring gear has the following code: 41B16 GM H329 1, of course 41/16 gives the ratio of 2.56. You kind of wonder why someone would match a 2.56 gear ratio with a posi?

    It would be interesting to take a look at a few more carriers from the 71-76 9 3/8 generation to see if the 759-761 series continues for the different versions available, to determine which carrier fits which gears etc. We have seen one thing, and that is that the 2.56 ratio has a different carrier to the 3.23 ratio (could it be a Olds thing only?), since the 2.56 wasn't available for the big Buicks. :Do No:
  8. EEE

    EEE Straight out of lo-cash!

    The numbers look like they're put on there in a differently designed way though.
  9. quicksabre

    quicksabre Well-Known Member

    We once used a 2.56 Olds posi carrier with a 2.93 gear and it took a roughly 1/4" ring gear spacer to make it happen. You could do the same thing with a 2.73-3.23 carrier and a 3.42 gear.
    That was a strange deal. It was a '70 Olds carrier from a Delta, going into a 73 rearend. The spline pitch in the '70 side gears did not match that of the 73 axles. 70 axles were too short for the 73 rearend. Spline count was the same at 31. We had to get the 73 axles cut to match.
  10. bob k. mando

    bob k. mando Guest

    the 3.42 looks like a heavy duty unit (extra ribs), as one might expect for something likely to see towing ( drag? :Brow: ) duty.
  11. quicksabre

    quicksabre Well-Known Member

    I've had a chance to do some more research with the 9 3/8" rear. This applies to the 1971-75 version, which I run in both of my big block 76 LeSabres. This rearend design was gone by 76, but it fits up to 76.
    This started because I burned up another set of posi clutches in mine at the track. It kept wanting to spin the right side only with slicks in the waterbox. Then it would slowly try to engage itself as the right tire got hot and sticky. I would stop and start the burnout while really laying on the brakes trying to get it to lock up, but the damage was done. This is the second time, and fresh clutches only fix the problem for a short time. Seems the slicks in the water aren't providing enough resistance or torque load to energize the clutch pack, even though on the street it wasn't an issue.
    So I set out to replace that feeble "S" preload spring in the posi unit. The unit needs much more preload. After I would burn these things up, it would only take about 30 ft lbs to make it slip. Replacing the clutches would bring it back up to about 100 or so, but that is still not near enough for the track.
    I went through some posi unit parts I had and found some Eaton posi springs and spring plates. It looked like they would fit if the plates weren't quite as wide. So I narrowed a set and installed them with 400lb springs. The fit was good after modification, and it now took closer to 200ft lbs of axle torque to make the unit slip. But I was wanting more, and I was starting to worry about affecting the hardness of the plates with all of the welding.
    So with more digging through boxes of parts, I found a set of Auburn preload plates and springs for an Auburn posi 8.5" corporate GM application. Turns out the Auburn setup is a an exact drop in. Even the crossshaft was identical. In fact, I used the Auburn cross shaft. So maybe there is an actual use for the Auburn design, the rest of which I do not like. The cross shaft hole dia.(as mentioned above) and spring compression are perfect, as if designed for the 9 3/8" posi. The Auburns, with their cone type clutches, use lots of preload, so it was real fun to install. But I got it in and not even 600 ft lbs. of axle torque will make it slip. May need to find some lighter springs, but these are the plates to use.
    Here is a picture of the plates. From left to right. Stock Eaton plates/springs, then the narrowed Eaton plates/springs, then the Auburn plates/springs, and finally the stock feeble "S" spring with a picture of it installed.

    Attached Files:

  12. quicksabre

    quicksabre Well-Known Member

    Here are the narrowed Eaton plates installed. Perhaps I will end up putting these back in if I can't find lighter springs for the Auburn plates.

    Attached Files:

  13. quicksabre

    quicksabre Well-Known Member

    Here are the Auburn plates and springs installed. The fit is absolutely perfect, but this provides tons of preload- more than I was really looking for. It will probably chatter really bad. We'll see. I will be testing it soon.

    Attached Files:

  14. SpecialWagon65

    SpecialWagon65 Ted Nagel

    Hey David, nice work- which track are you going to? I would like to see the LeSabre run. Ted:gp:
  15. quicksabre

    quicksabre Well-Known Member

    Well, it works quite well. I tested my modified posi in many situations today. All of that preload had me worried, but it still slips as it should on dry road. In the grass or on gravel, it does scuff the inside tire some on a sharp turn. But on a dry road it feels fine.
    For one of two harsh tests, I put the right tire in the grass along the road, and kept the left on the pavement. I powerbraked it some, and it still smoked the left tire, which was on the road. That takes a good posi. For the other test, I gassed it hard during a sharp right hand turn to see if it would put the right rear up in smoke. That did not happen, I instead just ended up doing a 180 in the intersection. That takes a good posi also.
    I don't think I will have any more single tire burnouts in the waterbox. As for the chatter I was expecting with all of this preload, it's not a problem so far.
  16. quicksabre

    quicksabre Well-Known Member

    Hey Ted,
    Thanks. My obsession with the 9 3/8" rearend lives on. The car appears to be worthy of drag duty again. I've been going up to Kilcare dragway. It's closer to where I work. So I drive the car to work that day, then just head over there for test'n'tune. They have theirs on Thursday evenings. Otherwise it would be Edgewater. From my house, they are both the same distance.
    I guess there is also Tri-state. I've never ran there though, only watched. It's by far the closest, I just don't know very much about the place.
    Do you ever make it up to Kilcare?
  17. grandville455

    grandville455 Well-Known Member

    Wow Thats good info to know!!! Sounds like a real strong posi now!
  18. 67RivRacer

    67RivRacer Well-Known Member

    Does anyone know the difference between a 66 and 67 3.42 posi carrier? I have a 66 posi/gear set up and would like to swap it into my 67 and I'm under the impression that the LH carrier bearing is larger on the 67, but the pics at the beginning of this thread seem to contradict this. The carrier I have has both carrier bearings the same size. I haven't pulled the cover off to examine the bearings yet. If the bearings are different, are the carriers the same, but just a different bearing used. Anyone know? Thanks
  19. quicksabre

    quicksabre Well-Known Member

    Look closely at the pics again. The left bearing(against the floor) is not so much bigger in diameter, it is wider- which would appear as height in the picture since the units are on their ends. So your original impression is correct.
  20. 67RivRacer

    67RivRacer Well-Known Member

    The posi I have on my garage floor has both bearing races the same size, .650" x 3.065"OD and the bearings appear to be the same as well. So this must be a '66 unit, correct?
    Will this '66 posi/ring/pinion swap into my '67 if the bearings are changed to the '67?

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