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37-41 FRONT Spring on the REAR of a stock Model a frame

Discussion in 'The Hokey Ass Message Board' started by Beau, Apr 8, 2012.

  1. Beau
    Joined: Jul 2, 2009
    Posts: 1,883

    Beau
    Member

    For some reason I thought I read about this swap...but I can't find a damn thing about it.

    I'm trying to lower the rear end without needing a large step. I'm gonna do a 4" sweep in the rear instead.

    I figure the flatter profile of the front spring will help lower the car a bit.

    I thought I also had read that it "rode like a brick" or something to that effect.

    I have a Model T Spring already, but a freind had a '39 front spring so I thought it would be worth some research.

    Any information is appreciated.
     
  2. F&J
    Joined: Apr 5, 2007
    Posts: 13,217

    F&J
    Member

    Are you mounting the spring behind the axle like a 32? I'm not up on A crossmembers with spring above, but I doubt the shallow arch will allow room to go spring above?


    I am using a 40 front in my stock 32 rear crossmember in a 32 with a open rear. I had to do a lot of spring leaf switching/eliminating, but I finally got it soft. Also, I found through trial and errors, that the shocks are just as important as the spring leaf eliminations.


    If you soften the spring to ride nice, the axle would slam the frame kicks, when going over a decent bump.

    I ended up finding a pair of shocks that compressed with the same resistance as they resisted expanding. Now the car does not come down quick enough to slam the axle against the frame kick, but still rides very smooth. Before, the many other shocks I had here, would compress a lot easier than they extend.
     
  3. Beau
    Joined: Jul 2, 2009
    Posts: 1,883

    Beau
    Member

    Sorry, I should have mentioned. I'm running the spring behind the axle.

    I looked back at the threads I had saved and most of the applications seem to be on '32 frame rails.
     
  4. F&J
    Joined: Apr 5, 2007
    Posts: 13,217

    F&J
    Member


    ok, then I will add that when you use the 40 style front spring, you need to plan ahead for what width and offset on rear tires/wheels.

    You can run out of room with wide tires, if it's full fenders, and if you don't want the wider tires sticking out beyond the fenders. Bias sizes that most of us use, are fine.


    One thing I found out about the front spring mock up in the rear: Several hambers said to set the rear perches at the same width as the donor front perches were. Don't quote me, but I thought that was 42.5". Whatever it was, it did not even come close to being correct on my car, at my ride height. Mine are way wider than stock front perches.
     
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  5. uponone
    Joined: Nov 26, 2008
    Posts: 112

    uponone
    Member

    i would also like to know about width of the spring perches....i have two front springs i might want to use for the rear end one is a 39 the other a 40(aftermarket)....the 40 only has like 7 leaves in it....the 39 has 10 or more....any suggestions.....does it matter if the spring is mounted in front or behind the rear axle
     
  6. F&J
    Joined: Apr 5, 2007
    Posts: 13,217

    F&J
    Member

    Here's some older pics of mine.

    Since then:

    -I took out many more leaves
    -I pushed the perches/bones outwards 1/2" more per side to get more shackle angle.


    My rear axle is early Olds and quite wide at 60" to wheel mount flanges.



    I spent a LOT of time fussing with the spring rate and shock rate to get it good enough around my property here. I am confident it is close enough for real world testing, but it's not registered/insured yet.


    As far as spring ahead of the rear axle; I can't see how it will clear the drive shaft IMO.
     

    Attached Files:

  7. Beau
    Joined: Jul 2, 2009
    Posts: 1,883

    Beau
    Member

    I have seen your posts before. I'm doing a simiar rear suspension set-up as yours. I have Ford 16" truck wheels with 6.00 tires. I did a rough measure for mounting the radius rods at the stock Model A with and it was really close to the backing plates (Bronco 9", 58" surface to surface)

    The information I have for the stock spring perch width is 38.5" center to center for '37-'41 front axle. That's pretty narrow. That's why I wondered how people are running these on the rear.
     
  8. F&J
    Joined: Apr 5, 2007
    Posts: 13,217

    F&J
    Member


    Not tonight, but i can measure the stock spring perch width on the front of my untouched 40 ford coupe.
     
  9. Beau
    Joined: Jul 2, 2009
    Posts: 1,883

    Beau
    Member

    Thanks, everything I read says 38 1/2" though. I suppoe the spring could be re-arched.
     
  10. uponone
    Joined: Nov 26, 2008
    Posts: 112

    uponone
    Member

    I have two spring one is 38.5 eye to eye the other is 40 eye to eye. Sag or different spring?
     
  11. Beau
    Joined: Jul 2, 2009
    Posts: 1,883

    Beau
    Member

    It's hard to say.
     
  12. F&J
    Joined: Apr 5, 2007
    Posts: 13,217

    F&J
    Member

    I measured the 40 Ford coupe front perch width at 42.5"

    Then I measured my 32 rear perch width at 47+. So, apparently my spring is not a 40 front, even though I took it out of a 40 Ford doodlebug. It was 4 years ago, and I don't recall looking at the spring setup whenI parted it out. So I guess some other spring was used, but I have no idea what year, or F or R?

    That doodlebug had a bolted solid TT truck rear end, so I know I did not have a 40 rear spring at that time.
     
  13. Beau
    Joined: Jul 2, 2009
    Posts: 1,883

    Beau
    Member

    Thanks F&J. I appreciate you taking the time to do that.

    For now I think I'll just stick with the Model T. Maybe I'll play around with the '39 front and see what I can do.
     
  14. chopt top kid
    Joined: Oct 13, 2009
    Posts: 959

    chopt top kid
    Member

    You can run the 37-41 front spring on the rear of a model A in a spring behind the axle configuration, but you have to mock up the rear crossmember to determine your requirements. I have no doubt that F&J had to spread his front spring out to decrease the arch in his front spring because the drop in the '32 rear crossmember would make his car way too high. Most who use the '37-'41 front spring on the rear use a flattened early Ford rear crossmember, use an aftermarket crossmember or fabricate one of their own. When using a flattened or straight crossmember, the distance between the spring mounting brackets should be 42 1/2"...

    I am using a '37-41 front spring on the rear of my coupe but I'm building a chassis using deuce rails and a flat aftermarket crossmember. I choose the '37-'40 front spring for the rear of my coupe because I am using a '69 Bronco 9" with a 58" wms to wms and needed something narrower than a stock rear spring. I would take some better pictures except right now I have the whole thing blown apart...

    The first pic shows the chassis for my coupe with just the '37-'41 main leaf mocked up with the aftermarket rear crossmember. The second pic gives an idea of the arch of the front spring mounted with the mounting brackets set at the 42 1/2" dimension. The last pic shows the rear axle of Brian Bass's coupe with a '37-'41 Ford front spring installed. Mr Bass used 42" for his perch to perch dim as that was what he needed to get the shackles to have a 45 degree installed angle. I hope he won't mind me using his pic...

    Here's the link to the thread that has the discussion about using the '37-'40 front spring on the rear... '40 spring help please
     

    Attached Files:

  15. Beau
    Joined: Jul 2, 2009
    Posts: 1,883

    Beau
    Member

    Thanks kid!

    This was the probelm I found. You have '32 rails, but the same basic idea. I also have the Bronco axle and the stock "A" spring is going to be real close to the backing plates. Back to the drawing board.
     

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