Register now to get rid of these ads!

Technical Which Ford 9" Posi Unit

Discussion in 'Traditional Hot Rods' started by bhemi, Sep 25, 2018.

  1. bhemi
    Joined: Sep 1, 2010
    Posts: 102

    bhemi
    Member

    I am getting a bare Currie 9" rear end housing with the frame mods on my '37 Buick build. I am looking at a menu of 28, 31 and 35 spline axles and options of Detroit locker, True Trac, Trac Loc and Wavetrac for posi units. I am going to running a 401 nailhead making no more than 450 hp on it's best day and 6 speed manual transmission. I will be running gears in the 3.70 -1 range as that will give me a 2100 - 2200 cruise at 70 mph in 6th gear. What is stout without being overkill?
     
    chevy57dude likes this.
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    True Trac if cost is not a problem.

    Locker if you want some fun.

    Get a spool if you really want some fun.

    31 splines, either way
     
    czuch, wackdaddy, fauj and 2 others like this.
  3. flamedabone
    Joined: Aug 3, 2001
    Posts: 5,441

    flamedabone
    ALLIANCE MEMBER

    I absolutely LOVE gear type differentials. We call them True-Trac as a generic term around my part of the country.

    I don't claim to fully understand what goes on inside them, (Squirrel can probably explain it) but they are super smooth, strong and always leave two nice long dark black marks. 31 spline is better from a strength standpoint mostly because the 31 spline doesn't taper down at the spline end like a 28.

    -Abone.
     
  4. USA Tires Sign Joe
    Joined: Aug 13, 2006
    Posts: 1,072

    USA Tires Sign Joe
    Member
    from Western NJ

    31 spline for sure you will snap the 28. I speak from experience.....an embarrassing moment I would like to forget LOL!
     
    chevy57dude likes this.

  5. bhemi
    Joined: Sep 1, 2010
    Posts: 102

    bhemi
    Member

    What Currie says :

    Truetrac and Wavetrac - Helical gear limited slip differentials (HGLSD) are the modern replacement for the classic clutch style limited slip differential. Under normal driving conditions, HGLSDs operate as a standard or open differential, allowing one wheel to spin faster or slower as necessary without the noise or harsh operation of a clutch style limited slip. When a drive wheel begins to slip, the helical gears inside the differential automatically engage, transferring torque to both rear wheels to maximize traction. When the wheels regain traction, the differential resumes normal operation. Unlike traditional clutch type limited slip differentials, HGLSDs require no special oil additive or maintenance to replace worn and tired clutches, as these units have no wearable parts, require no special maintenance and maintain their torque bias for the life of the unit.
     
    Noswal, czuch and chevy57dude like this.
  6. Mr. Forbes has sound advice, as usual. The Tru Track is the seamless power transition you probably need. Testimonial : The Detroit Locker in mine is not a problem, no ''events'' to report even though I've been caught in some rain. The unlocking/locking is a not harsh. Car is so loud I can't say if the locker makes noise. It's like having a spool that lets go when it binds.
     
  7. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    I've put over 100k miles on lockers, with powerful engines, and never ran into anything...lots of driving in rain, too. The noise depends on which unit you have, some are quiet, the racing type are loud. You can tell it's there by the subtle way it moves the back of the car when you let on and off the gas on gentle curves, and it will spin both tires and make the rear end swing around if you're not careful, but it doesn't take long to learn how to drive with one. Any limited slip can cause similar issues on wet pavement, that's what they're for!
     
    chevy57dude and fauj like this.
  8. southcross2631
    Joined: Jan 20, 2013
    Posts: 4,413

    southcross2631
    Member

    Go 31 spline with a locker and you won't be sorry.
     
    Bandit Billy likes this.
  9. deathrowdave
    Joined: May 27, 2014
    Posts: 3,519

    deathrowdave
    ALLIANCE MEMBER
    from NKy

    Ha ha ! Snap a 28 spline ! Granted 31 and 35 spline are better I really don’t think you have much worries snapping a 28 spline Axle . I would be afraid of u joint , tires hooking up , and your abality to drive it out as more concern . But if you must have a 31 spline , Detroit Locker and N case with NASCAR bearing support , it’s good for Diesel torque .
     
  10. Lumpy
    Joined: Jan 1, 2005
    Posts: 122

    Lumpy
    ALLIANCE MEMBER

    I snapped a 28 spline right where you would expect, just after the splines at the tapper. I have a sub 3,000 pound A Sedan with a mild SBC and a Detroit Locker. If your tire roll out is not almost exact the locker will put constant pressure on the side with a shorter diameter. This "probably" won't be any issue 99% of the time.....but the 1 time you stab the loud pedal and it hooks that tire, the axle may have some fatigue and then BANG 1 wheel peel. I have since upgraded to a 31 spline (no taper) and Detroit Locker.

    As a side note I drove home from the HAMB Drags this year in a monsoon type rain. As long as you know what to expect and drive through curves at a steady speed (minimum throttle input) not on and off the go pedal it's all good. I will admit I did think about how exactly I was driving though because it can all go to sh*t real fast.
     
    fauj likes this.
  11. 1946caddy
    Joined: Dec 18, 2013
    Posts: 2,060

    1946caddy
    Member
    from washington

    I've got a 9" true lock 28 spline in my dodge project and it will weight in at about 2300 pounds. 411 gears with a 200 4r tranny and Curie axles. Curie told me that I would not be breaking their axles.
     
  12. bhemi
    Joined: Sep 1, 2010
    Posts: 102

    bhemi
    Member

    Thanks for the advice. After a bunch of reading I think True Trac is a good way to go. I grew up when Lockers, 12 Bolts and Dana 60's were must have rear ends and True Trac seems the next generation. I like the no wear and no special maintenance claims. I appreciate all the responses.
     
    chevy57dude likes this.
  13. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    The True Trac has been around over 50 years...but it didn't become popular until recently.
     
  14. Mr T body
    Joined: Nov 2, 2005
    Posts: 2,228

    Mr T body
    Alliance Vendor
    from BHC AZ

    True Trac and 31 spline. The so called "soft" lockers aren't and the lighter the vehicle the more jarring the engagement. Wait 'til you take that first turn, get on it and it finally engages...... hope it points you in the same direction each time.
     
  15. jimmy six
    Joined: Mar 21, 2006
    Posts: 14,802

    jimmy six
    ALLIANCE MEMBER

    Ran a Currie 28 spline in a Super Stock dirt 1/2 mile Camaro for 5 yrs with a mini-spool and never hurt an axle. I know dirt is not pavement....just sayin.
     
  16. gimpyshotrods
    Joined: May 20, 2009
    Posts: 23,264

    gimpyshotrods
    ALLIANCE MEMBER

    I run a TruTrac, or equivalent, in everything with two rear wheels, or in the case of the wife's German missile, the front.
     
    czuch likes this.
  17. Retrorod
    Joined: Jan 25, 2006
    Posts: 2,034

    Retrorod
    Member

    TruTrack for 20 years, smooth and quiet. I never hurt 31 spline axles with 400 hp.
     

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2021 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.