Difference between 3.23 and 3.73's?

Discussion in 'Got gears?' started by BLT4SPD, Jul 10, 2005.

  1. BLT4SPD

    BLT4SPD Well-Known Member

    I have a 70 GS 455 with a 4 speed muncie M-21 ( I think first gear is a 2.52 ) and a posi rear with 3.23's. The housing on the pumpkin is cracked, the wheel cylinders are bad, the brakes and cables are bad....All around the thing sucks. :af:

    I have a freind that has a 12 bolt 3.73 posi rear out of a chevelle that I have been nagging him to sell me. How much difference would I see if I were to swap them out? The car is not sluggish now, but with the power plant it has, it should have more power. If the difference is minimal, I'll just repair the rear I have, 12 bolts are going like hotcakes it seems today, and before I spend $1000 on a rear, I want to know I'll be getting some power out of it. :3gears:

    Please let ke know your thoughts........ :Smarty:
     
  2. crazyjackcsa

    crazyjackcsa Big and Untame

    Something to ask yourself is "How much Highway driving am I going to do?" I don't know how much of a difference it would make off the line or int he 1/4 mile. I say If it is a track car then go for it. The calculator on www.1bad69.com will give you a good idea of what kind of rpms you will be running at highway speeds. Depending on Tire height, you are propably running about 2300 at a 60mph cruising speed, that will rise by about 350rpm with the 3.73's
     
  3. BLT4SPD

    BLT4SPD Well-Known Member

    reply

    Trevor,

    wow, that thing is really cool... I dont do much highway driving. I generally just cruise in the car, but I do like to get up on it from time to time. If going with the 3.73's means that I wont be able to drive it on the highway, then I wont do it. I had a friend that had a 4 speed car with 4.11's in the rear, and he was going down the highway at a noisy 6,000 rpms....I dont want it to be like that, but if I can get some jump off the line and more power, Id do it.
     
  4. 71GS455

    71GS455 Best Package Wins!

    A change in gear ratio will give you approxmimately 0% power increase. However, it will put you into your power band quicker. It will also reduce your top speed, and increase your rpm's at any given speed - as you probably saw with the already linked calculator.

    Don't forget, it will also throw off your speedometer/odometer until you swap out the drive gear.
     
  5. Topless64-455

    Topless64-455 Well-Known Member

    If you do this I will buy your other gears and posi for my 70 GS 350 car. It is currently an open rear. Thanks :TU:
     
  6. D-Con

    D-Con Kills Rats and Mice

    For fooling around town, you'll really like the difference. If you don't mind cruising the highways at 65-70 with a little more engine noise than you are used to, then I think you'll like the change. Especially if you are running a larger cam.
     
  7. sailbrd

    sailbrd Well-Known Member

    The twelve bolt will be better in the long run. Stronger, more parts, etc.
     
  8. monzaz

    monzaz Jim

    housing.

    I have pontiac housings here if you need one. 40.00 with out axles 80.00 with axles. The guts should fit right in as long as the posi has both the same size carrier bearing on each side. You will probably need the axles since pontiac uses a inside the tube seal. Not sure but you may be able to use your axles in the pontiac housing with the outside oil seals. Anyone ever do this before? I have housings at home and will do a check if your interested. At work rigght now. I do not know cause i just never ran into that particular question...So I will probably just check anyways. I know for a fact that a pontiac axle WILL NOT work in a buick housing. I will get back to you on this... Jim
     
  9. BLT4SPD

    BLT4SPD Well-Known Member

    reply

    I am running the TA performance 500hp street cam....its mild to hot Id say. I dont really ever hit the highway, I mainly just cruise around my town and smoke 17 year olds that think they are badasses in their mom's car ( a new jersey pastime) Does anyone have a 12 bolt posi rear with 3.73's in it by chance? My friend is seeming to change his mind again about selling it.
     
  10. D-Con

    D-Con Kills Rats and Mice

    I think you are on the right track wit hthe 3.73's. :3gears:
     
  11. Bad Buick

    Bad Buick Foe Fiddy Five

    Correct me if I'm wrong, but I thouhgt all 64-72 Pontiacs used the 8.2 rear?
     
  12. BA

    BA Well-Known Member

    BLT4SPD,

    I also would bre interested in purchasing your present 10bolt rear for parts.


    Bill
     
  13. oPh

    oPh Well-Known Member

    Pontiac 8.2 housings will not accept '68-70 Buick 8.2 ring & pinion AND vice versa. Need a '70 buick 8.2 housing, it needs to be a '70 Buick 8.2 housing.

    Interchangeability...
    Some '68-70 Buick 8.2 posi's can be used in Pontiac 8.2 rears, if close enough "stagger", & correct carrier bearing is used on lh side of carrier. Going other way, Pontiac 8.2 carrier in a '68-70 Buick rear... one will have to make a bushing to heat up & slip on lh carrier bearing boss, then can press on LM601312 bearing.
    :3gears:
    Roger
     
  14. BA

    BA Well-Known Member

    Hey Roger,

    On the Pontiac carrier you also have to open up the ring gear holes. Right? :Do No: What kind of tolerances are needed on the bushing?


    Bill
     
  15. oPh

    oPh Well-Known Member

    BA,
    If you can find a '70-72 Pontiac 8.2 carrier, it will have larger ring gear bolt holes. On the bushing, local machinist buddy made two for me several years ago, never kept his notes. Did put carrier in the freezer overnight & heated the bushing up on the cooktop, both bushing installations slipped right on. First one I tried to use red loctite on, but the hot bushing did not like it. Neither did my wife :rolleyes:

    Roger
     
  16. BA

    BA Well-Known Member

    So what's cooking at Rogers ranch? Rear ends of course :grin:
    Don't think my wife would go for that either?

    Thanks Roger I have a 69 Carrier which has smaller ring gear holes they must have opened them up after 69?

    Bill
     
  17. monzaz

    monzaz Jim

    8.2 buick

    Well I guess I have never run ito a 8.2 buick rear then. I have never run across a gear side bearing bigger then the non gear side. All the diferentials carrier from 8.2 all interchange in all the housings I have. Pontiac 2 Diagonal upper and 2 horizontal lower) and looks like buick think it is a 66 or 67 cause it has flat perches and small upper bushings(only one support web horizontal lower) The only differences I have run across are the carrier ring gear bolts right hand thread small(64-67) and left hand thread large (1968- 72). I have heard about the 68-70 buick weird rears... Not seen it for myself though. I would open it to be sure before working yourself up about it. Jim :TU:
     
  18. oPh

    oPh Well-Known Member

    The '68-70 Buick 8.2 is def a strange one. Lh bearing is same as 12 bolt Chevy (had a typo on number earlier).

    Jim, on your small bushing 8.2 A-body housing, it should be a '64 housing. Good buddy of mine, Chevelle vendor, was 1st to point out to me the uniqueness of the '64 rearends upper perchs & small bushings. Had not got to build any '64 8.2's at the time, so it was "cool deal", lol.

    Oddly, Chevelle vendor & I each have whats left of two '64 Olds 442 post cars. The rearends in both are 8.2 made by Buick axle plant with single rib housing... not that strong. Out of the one I mothballed, the axles (w new bearings) shipped out to fellow in CA w/ 64 LeMans. Even though Hollander shows different axle, they slid right in his '64 Pontiac 8.2 rear.
    :3gears:
    Roger
     
  19. monzaz

    monzaz Jim

    1964 axle

    Yes exactly . The axles were the same as a firebird axle I had laying around even had the inside the tube seals too. Jim
     

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