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Hot Rods How to build a transverse leaf spring rear?

Discussion in 'The Hokey Ass Message Board' started by flatheadfever, Mar 17, 2020.

  1. I have a narrowed 8.8 Explorer rear and a early 9”bronco rear that I want to mount a transverse rear spring to. These will be used on 35-40 ford frames.
    I guess my questions are:
    1/ Spring perch mount relative to pinion angle. ( I checked a stock banjo rear and the spring perch is the same angle as the torque tube.)
    2/ Spring perch distance to backing plate. ( to allow enough room for tires)
    3/ Spring length and arch relative to distance between spring perches. (Eye to eye distance and main spring length) I need to be able to go to the spring shop with exact specs to build a spring.
  2. Weedburner 40
    Joined: Jan 26, 2006
    Posts: 853

    Weedburner 40

    If yo are going to have a custom spring built, the distance between the perches won't really matter, just keep enough space from the backing plates to clear the perch, and inch or so. The perch shouldn't extend much past the backing plate from the axle centerline. Set the frame up and determine pinion angle, then make the perch parallel with the mounting point of the crossmember. Spring length should be 2 1/2" shorter than the centerline dimension between the perches. Arch is something you may want to talk to the spring company about but, probably 3" to 4".
  3. treb11
    Joined: Jan 21, 2006
    Posts: 3,691


    whats wrong with the original springs? If you have them, they can be used as patterns and measure the perch locations on the original banjo rear, again if you have them. I don't see a benefit to narrowed springs, as inset tires will hit the framerail first.
    X38 likes this.
    Joined: Jun 6, 2007
    Posts: 3,780


    I don't know if my pics will help but here is how I built my champ car rear end. I used a TT truck rear spring with leaves removed. I just made the perches so the hangers are at about a 45 degree angle when the chassis is loaded.

    Attached Files:

  5. The 40 ford front spring works really nice on a narrow rear or fat tires.
    There’s a few things you’re going to have to keep in line and mobile yet controlled.
    You need a good location of axle CL to frame.
    Axle CL to spring distance.
    Pretty damn close ride height
    Pinion angle.

    Around page 3 I start the rear end with all that stuff. I’ve got racked up frame tails, narrowed 8.8 exploder, 40 front spring. Modified crossmember.
    Last edited: Mar 17, 2020
    Atwater Mike likes this.
  6. Is there a secret formula for the main leaf spring length in relationship to the spring perches?
    I looked on the posies site. You tell them your spring perch distance and they make a spring.
    I just had a local spring shop make me a front spring. My original Ford spring had half the leafs broken. They made me a spring reversed with buttons. At first the main leaf looked exactly the same length. It turns out to be about 3/4 of an inch shorter and I cannot stretch enough to make it up with inch and a half shackles. I either need a longer shackles or another main leaf built. It seems strange that 1 or 3/4 inch would stop it from going together.
    Thanks for all the replies so far. This is getting me on the right track
  7. The ford springs are installed with preload tension. Meaning you need to flatten the spring some to install it. Reducing the curve height naturally increases the eye to eye
    Regular eyes you can use a spreader, reversed eyes needs a flattener. I use a square tube, a beefy clamp plus a quickly centering nub
    Atwater Mike likes this.
  8. rusty valley
    Joined: Oct 25, 2014
    Posts: 2,818

    rusty valley

    if you put the main leaf on by itself, you can do it without a spring spreader, then assemble the rest of the leaves once the shackles are hooked up
    Atwater Mike likes this.
  9. I,used Two pieces of angle to the top and bottom for the spring bolted together. used my port a power to spread the spring. Had the darn thing almost flat. Got it almost Hooked up. It seemed to be excessively flat. It is less than 1inch shorter than stock.
  10. Got any pics of old next to new? A side by side.
  11. I will in 2 weeks when/ if I get home.
  12. I used a transverse mono spring for a 40 Ford when I we installed the 9" Bronco rear axle under my '32 pickup, I also use a set of Pete & Jake ladder bars and spring mounts from Speedway motors. HRP




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