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Technical rear axle center

Discussion in 'Traditional Hot Rods' started by buick bill, Oct 18, 2019.

  1. buick bill
    Joined: Dec 18, 2008
    Posts: 269

    buick bill
    from yreka;ca

    been looking and cant find a real answer as to why gm set their closed drive cars/ p/us rear axles so far forward ? had to be a reason !!!! or was everyone blind back then ??
  2. Hnstray
    Joined: Aug 23, 2009
    Posts: 10,672

    from Quincy, IL

    @buick bill As weight is added to the vehicle (passengers/cargo) the arched spring compresses, effectively lengthening the spring. Given the front of the spring is anchored by a fixed mount, unlike the rear with a movable shackle, the lengthening moves the axle rearward and the visual placement of the wheel in the fender opening improves. Were it centered from the beginning, it would move to a rearward bias position and be more displeasing to the eye than it’s initial forward placement.

    Anyway, that’s my theory ........

    Last edited: Oct 18, 2019
    trikejunkie and Jibs like this.
  3. scrap metal 48
    Joined: Sep 6, 2009
    Posts: 5,648

    scrap metal 48

    I'm not sure I buy that^^^.. But it's better then I can come up with...
    Texas Webb likes this.
  4. squirrel
    Joined: Sep 23, 2004
    Posts: 43,429


    My hypothesis is that the shape of the wheel opening is such that the wheel is indeed centered under the top center of the opening...but the lower edges of the wheel opening are further back, because this gives the wheel opening a more streamlined shape.

    It's subtle, but it's there.
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  5. jaw22w
    Joined: Mar 2, 2013
    Posts: 834

    from Indiana

    Did you ever notice that the rear wheel on a model T is forward of center in the rear fender, and not because of parallel leafs moving the rear end back. I had to move the rear end back 3/4"to center the tire in the opening. I also had to move the front end forward about 3/4" to center the tire in the opening. So GM wasn't the only one.
    If a car has the wheels not centered in the fender openings that will be the first thing I notice. I'm like squirrel. I like to see the center of the wheel at the top center of the wheel opening arch.
    Hnstray likes this.
  6. buick bill
    Joined: Dec 18, 2008
    Posts: 269

    buick bill
    from yreka;ca

    I subed the rear of my 55 burbn with a jag in the garage . no side clearance/ view . rolled it out . took a look and rolled it back in cut it loose and moved it back 2 inches . never do that again !!
  7. Desoto291Hemi
    Joined: Apr 21, 2009
    Posts: 735


    Can you imagine how fast those cars were assembled back then,,,,,ever watched an old video of it.
    They were in a crazy hurry,,,,it’s a miracle they are centered as close as they are !

    Texas Webb likes this.
  8. oj
    Joined: Jul 27, 2008
    Posts: 6,131


    I always figured it was for the mud & snow buildup behind the tires driving dirt roads.

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