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Thread: Rear Suspension Bagging Thread>>>> Add Info!!!!!!!

  1. #1
    will work for food! phatfarmer2's Avatar
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    Rear Suspension Bagging Thread>>>> Add Info!!!!!!!

    so the purpose of this thread is too post up useful information on buliding a 3 link 4 link and so on... Proper angles, rules of thumbs w/e.. any info is helpful! All info will be consolidated and then made into a sticky. SO POST UP!
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    Registered User flnole78's Avatar
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    These are just a few guidlines I go by when designing a 3/4/5/6 link..

    1.Set pinion angles at ride height
    2.Typically you want the degree of triangulation to be around 40 degrees with 45 degrees being optimal
    3. While at ride height you want the lower bars parallel to the ground
    4. I tend to set the instant center near the back of the grille.
    (Instant center is where you draw an imaginary line through your upper and lower bars and extend them out towards the front of the truck until they intersect. The point of intersection is the instant center.)
    5. You want the distance from the upper bar frame mount to the axle mount to be the same length as the distance from the lower bar frame mount to the axle mount to reduce/eliminate pinion angle change through the range of motion.
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  3. #3
    will work for food! phatfarmer2's Avatar
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    add more guys!!!!!!!!!!!!!
    Grounded 4 Life
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  4. #4
    streetissuecustoms.com low_blazer's Avatar
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    I'm just gonna cut and paste stuff from my old tech page, since I havent had a chance to migrate it over to the new site..

    Why Reverse 4-links Suck...still.

    Think of your truck in its stock configuration....as the wheels rotate, the axle wants to rotate the OPPOSITE direction, right? And this
    for-every-action-there-is-an-opposite-and-equal-reaction characteristic is what actual MOVES your vehicle...more or less.

    As the wheels rotate, the axle rotates the opposite way, inducing motive force into the vehicle....now, this IS a gross oversimplification, but it is a fact, nevertheless....what is MORE important is that all the OTHER drivetrain geometries...piniuon angle, anti-squat,
    nstant center....all VERY important geometries..are based on this physical arrangement.

    Think about braking, for a second.....in the stock configuration,, when you hit the brakes, what happens? Correct...the car has atendency to dip, the rear has a tendency to rise....but the rear is trying to rise "over" the front leaf spring mount, right? And the basic lever
    arrangement that is formed by the stock position of the axle and the leaf spring tries to lift the truck OVER the front leaf spring mount as the car brakes...follow?

    This characteristic has the benefit of creating a fulcrum, over which the truck is trying to "rise", and which induces downforce during braking.Lets talk about what happens during acceleration, for a moment....when you acclerate, the axle/leaf spring arangement has a tendency to want to "lift" the truck...and this is because the axle is inducing force down the centerline of the leaf spring, which forms a "lifting arm"....basically, motive force is transferred down the leaf spring to the approximate center of the vehicle, and this
    lifts the truck...which in turn transfers weight back over the axle, increasing tractive force at the tires....

    Finally....since the point at which the axle rotates, up and down, is centered around the front leaf spring mount...pinion angle stays within limits.Now then......what about that reverse 4 link?All bad, all the time. First off, when you arrange the links to the REAR of the truck...the axle will swing on those links, and EVERY time the axle goes up and down, those links pull the axle towards the REAR of the truck....

    Next...what about pinion angle? Well, reverse 4 links NEVER solve for pinion angle, because they ALWAYS make the pinion angle climb WAY positive, because the upper links are ALWAYS shorter than the lower ones...

    What about imparting motive force? Well, again...because the links are behind the axle, when the axle rotates, the links tend to pull the rear of the vehicle down....and this is NOT optimum.Finally, what about braking? This is where it gets REALLY scary.....on a reverse 4 link, when you hit the
    brakes....the links, which are oriented towards the REAR of the truck, want to rotate UP and OVER the axle.....or, more significantly, the axle wants to rotate DOWN and BEHIND the rear of the truck....DEFINITELY an unsafe arrangement.

    So, why are revers 4 links "popular"? Well, fortunately, they are becoming MUCH less popular, but the answer to the question is...because they require NO knowledge of vehicle dynamics, and they eliminate that pesky requirement to actually ENGINEER a solution to that gas
    tank location.
    Last edited by low_blazer; 05-27-2011 at 01:09 AM.
    Doug
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    Originally posted by S/T Lover
    That post would have made more sense if you would have just pissed all over the screen and posted a screen shot of that.

  5. #5
    streetissuecustoms.com low_blazer's Avatar
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    Considering a 2-link (Ladder Bar) Setup?


    What about Ladder Bars? From the perspective of a street-driven car,
    the basic problem is that the ladder bar design does not resolve for axle
    rotation, except in the vertical axis. Nothing against ladder bars, it's just
    that it's not an efficient method of suspension attachment for street
    cars. In their intended environment, a doorslammer drag car, ladder
    bars allow for a solid coupling and an easy determination of instant
    center. But as a street suspension, ladder bars are woefully inadequate.

    Visualize holding a door, like the front door of your house. In this
    visualization, you will be acting as the forward ladder bar mount. Orient
    the door so that you're holding the hinges; the door should be
    horizontal, held out away from you, and swinging, up and down, on the
    hinges. Now, visualize a wheel, one at each of the two outside corners
    opposite the hinges; the long edge of the door, opposite you, will be the
    rear axle.

    What we've done is to model a typical ladder bar suspension. To see
    how it works, visualize the door swinging up and down. As long as the
    door is pivoting on it's hinges, with no rotational forces involved,
    everything works great. Now, try moving the corners opposite you (The
    corners that we're calling "wheels") in different directions...one corner
    up, one corner down. See what happens? The door wants to rotate right
    out of your hands! This is precisely what happens when you turn a
    corner, or go up a driveway, in a ladder bar-equipped street car. Ouch!

    The design considerations necessary to resolve this problem include
    lengthening the bar, moving the front ladder bar mounting points closer
    together (triangulating), and using a large, soft bushing. Take a look
    underneath a mid-60's GM pickup ( or a Grand National stock car, for
    that matter...). Street rodders, look at the Pete & Jakes ladder bar
    design. All use long, triangulated bars with big bushings. The only
    ladder bar that even comes close is the Chassiswork's Pro Street bar,
    which doesn't use a triangulated design, but does use a urethane
    bushing.

    What's the bottom line? Obviously, ladder bars are very popular, likely
    because of the design's simplicity. The 4-link design is more complex,
    often requiring some engineering and fabrication. On the plus side, the
    4-link is a superior method of axle control, especially in street cars,
    offers infinite adjustablility, and is the only way to get your hot rod really
    low. So...think about it first. Design your ride for safety and longevity;
    don't use race-car parts or designs in street cars unless you're sure
    that they'll live.
    Doug
    '85 Blazer...bagged, small-blocked, back-halfed and body dropped
    http://streetissuecustoms.com/salesban_3.jpg
    Street Issue Customs

    For all your custom fiberglass, interior or stereo needs... Epicenter Designs

    Originally posted by S/T Lover
    That post would have made more sense if you would have just pissed all over the screen and posted a screen shot of that.

  6. #6
    will work for food! phatfarmer2's Avatar
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    anyone have more to add? would like to make a nice sticky for the site!
    Grounded 4 Life
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  7. #7
    Registered User scooterb's Avatar
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    run shocks and if u want to go with 1/2 line have sum line slow downs if not its goin up really fast!!!!!

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