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Technical Rear spring...on top or out back?

Discussion in 'Traditional Hot Rods' started by poboyross, Jun 3, 2020.

  1. poboyross
    Joined: Apr 29, 2009
    Posts: 2,142

    poboyross
    Member
    from West TN

    Man, y'all.......it's literally been YEARS since my last post. It's also been YEARS since I had a traditional hot rod, going on 5 now?!?!? SO, found myself an old T chassis, and I want to Z the rear. I've seen folks argue about where to put the transverse spring. Is it better to have it mounted on TOP or OUT BACK? My last Model A had the spring mounted out back of an old Chevy 10bolt rear end. It centered it in the wheel well area of the A body nicely. However, this time, there will be no such wheel well to worry about. I'm going to attempt to build my own speedster body, I got a crazy itch I want to scratch.
     
  2. fourspd2quad
    Joined: Jul 6, 2006
    Posts: 908

    fourspd2quad
    ALLIANCE MEMBER

    Spring behind axle setup is known to be a softer ride than spring over axle.
     
  3. clem
    Joined: Dec 20, 2006
    Posts: 4,188

    clem
    Member

    I would like to know the principles behind this comment, if possible ?
     
  4. fourspd2quad
    Joined: Jul 6, 2006
    Posts: 908

    fourspd2quad
    ALLIANCE MEMBER

    I am by no means an expert on suspensions nor do I have a ton of experience on the subject. I have heard this opinion mentioned enough by people who have experienced it to accept it to be true and it kind of makes sense to me.
    What I can envision though is that when a load is created on the system caused by a deviation in the road surface, it is transferred more directly to the frame in a spring over axle setup. The path of the load to the frame in a spring behind or in front of axle setup is not direct therefore the energy is absorbed somewhat by the torquing of the leaf spring. That is how I see it at least.....anybody else have any opinions?
     

  5. RidgeRunner
    Joined: Feb 9, 2007
    Posts: 906

    RidgeRunner
    Member
    from Western MA

    It's been said that where the suspension attaches to the chassis sets the effective wheelbase that the car actually "feels". Longer wheelbase cars generally ride better, think wheel base differences between "standard" models vs "luxury" model and their ride comfort qualities over the years.

    With transverse springs attachments behind axle center line on rear and ahead of axle center line on front it results in a longer effective wheelbase than the defined standard axle center line to axle center line.

    Wheel base for handling qualities desired for different applications opens up a whole 'nuther deal.

    Ed
     
  6. fourspd2quad
    Joined: Jul 6, 2006
    Posts: 908

    fourspd2quad
    ALLIANCE MEMBER

    Kind of surprised the isn't more of a response on this subject as most builders have had to decide which way to go.
     
  7. flatheadgary
    Joined: Jul 17, 2007
    Posts: 1,012

    flatheadgary
    Member
    from boron,ca

    i am a behind the axle kind of guy. my wife says i am a back door man, but we won't go into that. anyway, i have built several t bucket type cars and had the spring mounted both ways. i think they ride better behind. i do know that a spring behind on the front axle makes it ride better though.
     
  8. So you’re talking about the rear spring right?

    When it’s on top of the rear axle it’s a God awful rollercoaster Shaped spring with a very high and very stiff arch. T or A . There a bunch of spring material there that’s doing nothing and a small amount doing the work. The parts that are more towards vertical are not working, the parts that are more towards horizontal are.
    Then the ride height is up there,,, higher than giraffe pussy.

    Spring Behind out back utilizes the whole spring pack for ride control. It’s so much better in many aspects
     
  9. Mimilan
    Joined: Jun 13, 2019
    Posts: 1,230

    Mimilan
    Member

    If you used the same spring in both scenarios , it would be the opposite
    The only time this has no effect is when there is a 4 link system and the spring is attached to the housing and not a link [1" of axle travel will still equal 1" of spring travel]

    It alters the motion ratio which is calculated from the front pivot. The bones or A frame pivot on an Arc
    so [1" of axle travel could be 1" plus of spring travel]
    there is more travel and less spring stiffness needed at the spring when it is behind
     
    Last edited: Jun 6, 2020
  10. deucemac
    Joined: Aug 31, 2008
    Posts: 1,483

    deucemac
    Member

    By installing the spring behind the rear axle and in front of a front axle, you increase the "Spring base" 5 to 6 inches over the wheelbase. Effectively getting the benefits of say 118 wheel base ride on say, a 35 to 40 Ford 112 inch wheel base. You still benefit if only the rear spring is mounted behind the axle, just not as much as if both are between the front and rear transverse springs. I believe Ford did that to smooth out the ride and allow for the axles to sit lower in relation to the frame .
     
  11. One of these things just isn’t like the others
    3B12926C-D22A-4042-8877-FD962DA994AF.png

    0E8C10BE-71ED-4193-A610-FC9F1135F4C7.png


    FE3F4B45-2E3E-4068-9C4A-6D4ED0586B4B.jpeg
     
    fourspd2quad likes this.
  12. dumprat
    Joined: Dec 27, 2006
    Posts: 3,479

    dumprat
    Member
    from b.c.

    It has everything to do with leverage and nothing to do with wheelbase or mounting.
    It's a simple factor of the distance from the attachment point on the frame to where the springs is attached to the ladder bar, or wishbone. More distance between the frame mount and spring multiplies the leverage against the axle.

    There are lots of 4x4 suspension builders who will move or modify the spring and shock locations relative to the axle to change both the springs ability to control the axle movement and to generally increase the amount of suspension travel. Putting the spring closer to the frame mount gives more travel with a shorter spring but makes the spring less efficient.
     

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