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Technical Ladder Bar Suspension

Discussion in 'Traditional Hot Rods' started by Deuced Up!, Jan 6, 2014.

  1. Deuced Up!
    Joined: Feb 8, 2008
    Posts: 4,028

    Deuced Up!
    ALLIANCE MEMBER

    Anyone got any good tech articles or advice on Ladder Bar Suspensions? Starting to layout the rear suspension on straight axle gasser build. Thinking about length etc. In the old days I remember seeing 4 to 6 foot plus ladders under drag cars. What are the advantages of long versus short ladder bars?

    Specifics on my car: 850 hp 454, Doug Nash 5 Speed, 350 Rear Gear in Reinforced Ford 9" (with the Nash low first gear it is about the same as a 400 turbo with a 456 gear), 98" wheel base. GOAL, wheels up launch and hold them there for at least one shift if not two.
     
  2. saltflats
    Joined: Aug 14, 2007
    Posts: 10,730

    saltflats
    Member
    from Missouri

    Keep the crank center line up high and you will have wells up action.
     
  3. Deuced Up!
    Joined: Feb 8, 2008
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    Deuced Up!
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    Well as you can see the Crank Center Line is up there. Right around 25". My question though is about Ladder Bar length. I have heard shorter arms lift quicker etc. Any thoughts on that subject?
     

    Attached Files:

  4. Shorter bars hit/plant the tire harder with more body/rear tire separation, but less weight transfer & smaller wheelies. Longer bars give you more front end lift (weight transfer) & bigger wheelies, with less "hit" to the rear tire for less body separation. Stick cars don't typically use or need as much hit (shorter bar) because you are shocking/ getting a run so to speak at the rear tire when you dump the clutch. An auto with a trans brake reacts much the same. An auto with a foot brake though, can often use a shorter bar because the more you load the throttle against the converter, the more you preload the rear suspension and kill the "hit". Earlier Gassers used long bars for more front end lift/weight transfer, against the hard/stlff side wall tires of the day. Also if you try to put alot of hit (shorter) bar against a hard side wall, it will recoil after the initial hit, and actually, unload the tire. Most successful stick cars run biased ply slicks and street legal slicks because of this, where as a foot brake auto can get away with a stiffer side wall like a radial drag tire which will give you a little quicker 60 foot and ET, because there is less wind up in the side wall when the tire sticks on the leave. Many of the early gassers that used a single buggy spring with radius rods/ hair pins, used the same mount (typically about at the fire wall)for the hair pins & the ladder bars.., if you go that route, make sure the wheelie bars are on and you butt is puckered.
     

  5. Think of it this way. If you have a rectangle box, and you try to pick it up with a hand truck on the narrow side it only picks up the back of the box at the hand truck. Now if you try the hand truck on the long side, it picks up the whole box, leading edge first.
     
  6. Deuced Up!
    Joined: Feb 8, 2008
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    Deuced Up!
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    Exactly what I had thought. Thank you for the confirmation. I had several people telling me I was messing up putting long bars under the Austin but I knew I had read somewhere exactly what you explained here. Thanks again.
     
  7. Deuced Up!
    Joined: Feb 8, 2008
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    [QUOTE: Many of the early gassers that used a single buggy spring with radius rods/ hair pins, used the same mount (typically about at the fire wall)for the hair pins & the ladder bars.., if you go that route, make sure the wheelie bars are on and you butt is puckered.[/QUOTE]

    I am just about 18" aft of the firewall with nearly 5' bars. I chose to end there because that is where the original chassis' "X" member is placed. I made a plate bracket that connects the "X" member to frame rails right and left. The ladder bars mount there. However the "X" member front arms run all the way up to the engine mounts. I am ready to "pucker"!
     
    Last edited: Jan 7, 2014
  8. ardyboy
    Joined: Mar 5, 2008
    Posts: 664

    ardyboy

    I am just about 18" aft of the firewall with nearly 5' bars. I chose to end there because that is where the original chassis' "X" member is placed. I made a plate bracket that connects the "X" member to frame rails right and left. The ladder bars mount there. However the "X" member front arms run all the way up to the engine mounts. I am ready to "pucker"![/QUOTE]

    Dueced up---any chance you can show us a picture of that?
     
  9. Deuced Up!
    Joined: Feb 8, 2008
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    This is the Diagram I drew of the mount and how it will fit etc.

    [​IMG]
     
  10. whiskerz
    Joined: Jul 7, 2011
    Posts: 148

    whiskerz
    Member
    from Ga.

    Post a picture of this in action later
     
  11. mgtstumpy
    Joined: Jul 20, 2006
    Posts: 8,760

    mgtstumpy
    Member

    This is a formula by Pepe Estrada to calculate length. Found this in an old suspension book that I have.
     

    Attached Files:

  12. Deuced Up!
    Joined: Feb 8, 2008
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    That is a cool formula, thanks for posting. Running the numbers it says I need 30" ladder. Do you know what kind of driving that suspension formula was set up for...drag racing or average car etc. Just wondering if it noted what kind of driving that optimized that formula.

    I am afraid for me, I am going 20" further north...LOL
     
  13. 1971BB427
    Joined: Mar 6, 2010
    Posts: 6,762

    1971BB427
    Member
    from Oregon

    I thought the old rules said a ladder bar couldn't be more than half the wheelbase in length. But I see numerous examples of old cars running what look like longer ladder bars, so not sure whether the rule was enforced.
     
  14. brandon
    Joined: Jul 19, 2002
    Posts: 6,334

    brandon
    Member

    instant center...do you want to look cool or do you want it to work...:D
     
  15. Deuced Up!
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    Deuced Up!
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    Both!
     
  16. Larry T
    Joined: Nov 24, 2004
    Posts: 7,661

    Larry T
    Member

    Long ladder bars lift the front end, but the let the back end drop and that unloads the tires. But with today's track prep and slick compounds you probably won't have to worry about unloading the tires.

    NHRA always said max crank centerline was 24". But it probably won't get checked.

    Kinda sounds like you might need a weight box in the front of your car. I don't think not being able to do wheelstands is going to be a problem, maybe just the opposite.
     
    Last edited: Jan 8, 2014
  17. Deuced Up!
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    Thanks. I am not too worried about the NHRA, this is more of a Show/Go car to have fun with...At least that was the plan when it started. Originally we were just building a Gasser styled car to cruise. However it seems to be getting faster and faster and more full on old school Drag Car everyday.

    When it is all said and done it will still just be about the fun. We will still cruise it to area car shows and the Steak & Shake but when we leave the parking lot, trust me, everyone will know it! LOL!
     
  18. gnichols
    Joined: Mar 6, 2008
    Posts: 10,969

    gnichols
    Member
    from Tampa, FL

    Hoping to improve my tech question record (of late, anyway), just wondering... What is the difference between trailing / truck arm suspension and ladder bars? The reason I ask is that I find the automotive math here fascinating - calculating the lengths of the bars for racing - but I've never heard it discussed once with regards to building a street car (using SOCAL's long style bars that are very popular). Is it just that unimportant on a street car? Gary
     
  19. mgtstumpy
    Joined: Jul 20, 2006
    Posts: 8,760

    mgtstumpy
    Member

    Here's a 42 Chevy PU I'm doing for a friend. I added a 46 Olds centre X-member with the OEM Olds trailing arm setup. I need to add a panhard bar. Trailing arms are similar to the old Chevy c10 rear suspension. I had to step up the rear chassis to make it work.
     

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  20. brandon
    Joined: Jul 19, 2002
    Posts: 6,334

    brandon
    Member

    do a little plotting and laying stuff out on a side shot (drawing or photo) of the car ...decide how high and where you want to position stuff... crazy angles and high ic , and you'll be living on tire, sure it will work , but you'll be tire dependant. :eek: there are ways to achieve what your wanting...

    I was told by a chassis manufacturer, level the bottom bar and go 3 down on the pinion...not sure how that fits in to your plan
     
  21. On my street freak '42 Chevy coupe, I am using a S&W Gasser ladder bar that is 42" long as I want to put a show on when my 8-71 Dart 540 with a Lenco is making that fun! :D I had Sid of www.droppedaxles.com undrop and drill a 47-55 Chevy pickup I-beam axle for the front. I have gathered all the parts and hope to start this spring, when other projects leave the shop! :D Will post pics then.

    [​IMG]

    [​IMG]
     
    Last edited: Jan 9, 2014
  22. Mike VV
    Joined: Sep 28, 2010
    Posts: 2,347

    Mike VV
    Member
    from SoCal

    Dueced -

    If you want full use of the action of your bars...don't forget about the shocks...!
    If you have stiff 50-50 shocks...not much is going to happen in any direction...!

    Might be a good idea to go look into Jerry Bickels suspension book before you go too far. It's very informative reading. While mostly race stuff, it can be used on the street with some thought.

    Mike
     
  23. brandon
    Joined: Jul 19, 2002
    Posts: 6,334

    brandon
    Member

    good point... allow as much up travel on the fronts as possible.
     
  24. indyjps
    Joined: Feb 21, 2007
    Posts: 4,160

    indyjps
    Member

    Check the websites of the chassis companies, I remember them having good diagrams for geometry to help people order 4 links and ladderbars. Been a while since I've needed them so I can't make a recommendation.
     
  25. Deuced Up!
    Joined: Feb 8, 2008
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    Yes good call. I have 90/10s Bilsteins up front. I was thinking about putting an adjustable shock up there to have some kind of adjustment in case it is transferring too quickly etc. But I already had the Bilsteins so we will start there and see what happens. Very good point though.
     
  26. brandon
    Joined: Jul 19, 2002
    Posts: 6,334

    brandon
    Member

    a good rear shock will take care of some the quick front.....:eek:
     
  27. Deuced Up!
    Joined: Feb 8, 2008
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    They basically work the same. Both have a single front mount, the real difference is the rear mounting system. Ladders bolt to a vertical bracket on the axle housing one mounting point above the axle and one below. The Trailing arms mount using two vertical bolts that pass through the trailing arm and the axle pad on either side front and rear of axle housing.
     
  28. gnichols
    Joined: Mar 6, 2008
    Posts: 10,969

    gnichols
    Member
    from Tampa, FL

    Thanx. Forgot to ask, would the racer math be the same for calculating length? Gary
     
  29. Deuced Up!
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    Deuced Up!
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    Not sure about that, maybe someone else can chime in. On paper you would think so however it seems most of the truck arm are angled in from the outer axle area to the center area of the chassis. Not sure if that or the mounting style affects the math. There is a Truck Arm thread running as well here at the moment, one of those guys might be able to answer the question: http://www.jalopyjournal.com/forum/showthread.php?t=523987
     
  30. Deuced Up!
    Joined: Feb 8, 2008
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    Deuced Up!
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    Well here is one of them. More photos of the construction etc. in my Austin Somerset Album here on the H.A.M.B. This is the backside of the passenger side Ladder. Still have some grinding and cleaning up to do but your get the idea.

    [​IMG]
     

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