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Technical Need help deciding which rear axle

Discussion in 'Traditional Customs' started by RMONTY, Jun 8, 2016.

  1. RMONTY
    Joined: Jan 7, 2016
    Posts: 2,218

    RMONTY
    Member

    I am building a wilder than mild but milder than wild 235 for my 1950 Chevy Sedan Delivery. I picked up a T5 transmission recently, and am now looking for a rear axle to get rid of the torque tube.

    I found a rear axle in a 1996 S10 4x4 Blazer, and it has the codes GT4 and G80 in the glovebox. From what I can tell, the GT4 tells me this is a 3.73 and the G80 is a limited slip diff.

    I am not well versed in "gearing", so I'm hoping someone can tell me if this will be a good rear axle.

    I want to be able to make some noise and wake up some people off the line, but also want to have good highway cruise capability.
     
  2. Phil1934
    Joined: Jun 24, 2001
    Posts: 2,717

    Phil1934
    Member

    27" diameter tire is 747 revolutions per mile x 3.73 = 2786 RPM at 60 MPH. I would want that much gear for a 235 even though 70 MPH is out for comfortable cruising as it is going to push it to 3250.
     
  3. With the T5 trans, that should be about perfect....
     
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  4. Phil1934
    Joined: Jun 24, 2001
    Posts: 2,717

    Phil1934
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    I forgot about that. Figure about 0.70 OD in for about 2000 at 60, 2300 at 70.
     
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  5. wheeldog57
    Joined: Dec 6, 2013
    Posts: 2,039

    wheeldog57
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    You should be very happy w/ 3.73 posi gears. Smoke 'em up!

    Sent from my SM-G900V using H.A.M.B. mobile app
     
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  6. gimpyshotrods
    Joined: May 20, 2009
    Posts: 18,365

    gimpyshotrods
    ALLIANCE MEMBER

    That's dead-on what I would choose.

    Just make sure that you get the hole for your spring pins in the proper place in the leaf spring perches.

    It ain't centered like on "modern" car that started life with an open driveline. Miss that, and your wheels will be about 1-1/2" too far forward.
     
  7. I agree, the 3.73 is a good choice for your T-5 trans and 235 combo. Also 31Vicky is right, the gov-lock is not a limited slip. But with your 235 and T-5 you are not exactly going to be too much worry about burnouts.
     
  8. Torkwrench
    Joined: Jan 28, 2005
    Posts: 2,521

    Torkwrench
    Member

    I'd look for a 55 - 57 Chevy passenger car rear axel. It's practically a bolt in for a 50 Chevy. Parts availability is good. It's also a strong rear axel, although many will disagree with this. Much stronger than an S-10 rear axel. After all, this is what was in 425 hp. 409 Chevys, as well as 1963 Z-11 427 Chevys.
     
  9. jlckmj
    Joined: Oct 28, 2008
    Posts: 59

    jlckmj
    Member

    The 3.73 should be great for highway cruising with the T5.
    I have a 235 with a T5 and S10 4x4 rear end ( 3.42 gears ) in my wagon and I love it.

    If your T5 is from a S10 and has the 4.03 first gear (like mine) it is a bit much for take offs. I have to shift out of first gear 3/4 the way through an intersection. If it is from a firebird / camaro and has a 2.90 to 3.00 ish first gear, it will be perfect.
    I agree with the poster above that stated the tri five is a better rear end, but they are also harder to find, and 4 times the cost of the S10. The S10 4x4 is within a half inch of the stock rear end.

    Jim
     
  10. RMONTY
    Joined: Jan 7, 2016
    Posts: 2,218

    RMONTY
    Member

    The T5 is from a 1988 S10 pickup. I don't know if any of the gearing has been changed, it may have been. The T5 has 1988 and 1987 castings, and I can tell it has been apart at some point.

    I keep seeing everyone say a tri five rear end is the best to use, but I haven't found one for less than $500 in this part of the world. The guy wants a buck-fifty for the S10 rear end. Seemed like a reasonable price to me.
     
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  11. gimpyshotrods
    Joined: May 20, 2009
    Posts: 18,365

    gimpyshotrods
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    You can only chance all gears 1-4, or 5. I have never heard of charging all 1-4 (linked). I have changed 5th.
     
  12. RMONTY
    Joined: Jan 7, 2016
    Posts: 2,218

    RMONTY
    Member

    Good info Gimpy...thanks!

    So what kind of difference would it make if I went with a 3.42 rear end. I am still trying to wrap my head around the gearing....
     
  13. gimpyshotrods
    Joined: May 20, 2009
    Posts: 18,365

    gimpyshotrods
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    That might be a better gear for a V8. You don't want to be way under the torque peak. It's like shifting into too high a gear too soon, you will strain the engine.

    My gearing philosophy has always been, better to turn the engine a little fast, than a little too slowly.

    Yes, your engine will turn a little faster with the lower gear (numerically higher) than the higher one (numerically lower), but it will do so with less load, due to the mechanical advantage that the gear provides.
     
  14. gimpyshotrods
    Joined: May 20, 2009
    Posts: 18,365

    gimpyshotrods
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    Now remember, there are TWO S10 ratio sets. One has a 3.76 first gear, and a 0.72 overdrive. The other has a 4.03 first gear, and a 0.89 overdrive.

    That second one is less common, at least where I am, but it would work with the 3.42 rear gear.
     
  15. Gary Addcox
    Joined: Aug 28, 2009
    Posts: 2,435

    Gary Addcox
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    I run the same rear gear with a 700R-4 and 31" tires. It turns 2100 rpm's @ 75 mph and comes out of the hole strong with that low first gear.
     
  16. gimpyshotrods
    Joined: May 20, 2009
    Posts: 18,365

    gimpyshotrods
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    You, of course, have the advantage of torque multiplication from the converter, too, so the launch is stronger.

    However, the OP's tires are shorter, so his hole-shot should be good, too.
     
  17. RMONTY
    Joined: Jan 7, 2016
    Posts: 2,218

    RMONTY
    Member

    Out of curiosity, and the need to know, and the fact that Craigslist is what it is....what are the pro/cons of going with a rear diff that ISNT a governor lock, gov loc, etc? It seems the G80 is no longer available. I did locate one that isn't a G80 however.
     
  18. Your 235 isn't going to be a tire burner, so single legger rear is fine. Nice to have the gov-lock, but I would not pass on an open std diff rear if it was good shape and good price.

    Another rearend to consider is the second gen Camaro/Firechicken (70-81). These are the bigger stronger 8.5 10-bolt, and a lot easier to find than the 55-57 rearends. Be careful as many of the Camaro rears were pretty high gear remember these were the 70's smog and pre-OD days, but you can find them with 3.73 and plus or minus either way. It will be about the same width as your stock rearend.
     
  19. RMONTY
    Joined: Jan 7, 2016
    Posts: 2,218

    RMONTY
    Member

     
  20. RMONTY
    Joined: Jan 7, 2016
    Posts: 2,218

    RMONTY
    Member

    Picked up a GT4 S10 4x4 for a decent price... 99 and a 14 core I think. Brakes look great and there is no sign of any kind o' leakage. Now to figure out which rear end kit to go with. Gearing is supposed to be 3:73 I believe...
     

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