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Thread: Don't box your L body subframe, here's why.

  1. #21
    Supporting Member II Turbo Mopar Contributor Shadow's Avatar
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    Re: Don't box your L body subframe, here's why.

    Quote Originally Posted by tryingbe View Post
    Fully independent suspension would be my guess.
    Bingo

    Robert Mclellan
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  2. #22
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    Re: Don't box your L body subframe, here's why.

    that neon rear suspension looks very cost effective - at least from a manufacturer's point of view

    even if it does look like it's made outta some twigs (or because)

  3. #23
    Supporting Member II Turbo Mopar Contributor
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    Re: Don't box your L body subframe, here's why.

    Fully independent yes, but some kind of anti-roll mechanism has to be a part of it too, right?
    John Laing

    "The sole condition which is required in order to succeed in centralizing the supreme power in a democratic community, is to love equality, or to get men to believe you love it. Thus the science of despotism, which was once so complex is simplified, and reduced . . . . to a single principle."
    -- Alexis de Tocqueville

    "One of the methods used by statists to destroy capitalism consists in establishing controls that tie a given industry hand and foot, making it unable to solve its problems, then declaring that freedom has failed and stronger controls are necessary."
    --Ayn Rand

    "To evolve, you don't need a Constitution. All you need is a legislature and a ballot box . . . . things will evolve as much as you want. All of these changes can come about democratically; you don't need a Constitution to do that and it's not the function of a Constitution to do that."
    -- Justice Antonin Scalia

  4. #24
    Supporting Member II Turbo Mopar Contributor
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    Re: Don't box your L body subframe, here's why.

    The only advantages to a fully independent suspension on a FWD are slightly better ride, NVH, weight (to a point), better dynamic chassis control, and bragging rights...maybe more room to route exhaust, etc. In some instances it can help performance, but from an autocross or road course perspective the twist beam and semi-trailing arm suspension set-ups have proven to be just as effective and can perform just as well or better than a full IRS. Remember, once you jack the inside wheel off the ground, no matter what type of suspension, you have 100% weight transfer. This will happen to ANY FWD car with a high degree of rear anti-roll stiffness...which most high performance type FWD cars do to help front traction and turn-in.

  5. #25
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    Re: Don't box your L body subframe, here's why.

    Quote Originally Posted by tryingbe View Post
    1-1/8 inch poly bar with no stock sway bar.
    http://polybushings.com/pages/swaybarLrr.html
    Be careful, that was my exact setup.

  6. #26
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    Re: Don't box your L body subframe, here's why.

    stone cold stock the shelby charger suspension worked great when still only 3-4 years old

    really good rear shocks were a must
    many were already dead by then

    I didn't have issues with it wanting to rotate at anything under 50 mph going around a decient curve in an on ramp

    but turn left or right at speed onto any side street on 3 wheels - yeah no problem

    .. unless your sitting in the back and not wearing a seat belt

    lolololol

    my buddy ... the thump he made as he hit the driver's side rear interior panel ...

    though I did learn to keep the tires with the most tread on the back as the worn ones will let the rear rotate really badly in the rain or wet as there's simply not enough weight to keep the car in place without the extra tread to grip with

  7. #27
    Moderator Turbo Mopar Staff Force Fed Mopar's Avatar
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    Re: Don't box your L body subframe, here's why.

    Quote Originally Posted by Dr. Johny Dodge View Post

    though I did learn to keep the tires with the most tread on the back as the worn ones will let the rear rotate really badly in the rain or wet as there's simply not enough weight to keep the car in place without the extra tread to grip with
    This is what happened to my GLHS...

    Rob M.
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    2.5 TIII swap is here!

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  8. #28
    Supporting Member II Turbo Mopar Contributor Shadow's Avatar
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    Re: Don't box your L body subframe, here's why.

    Quote Originally Posted by johnl View Post
    Fully independent yes, but some kind of anti-roll mechanism has to be a part of it too, right?
    Correct. More important on the rear then the front

    Robert Mclellan
    http://www.youtube.com/watch?v=wambNdfnu5M
    10.04 @ 143.28mph (144.82 highest mph)
    Worlds fastest 8v MTX Shelby Charger
    Manitoba's Fastest 4cyl!
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    New clutch combo is the SH!T!

  9. #29
    turbo addict Pat's Avatar
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    Re: Don't box your L body subframe, here's why.

    Quote Originally Posted by Shadow View Post
    Correct. More important on the rear then the front

    That really depends on spring rates, where the weight on the car is and what the cars intended use is.

  10. #30
    Supporting Member Turbo Mopar Contributor GLHS60's Avatar
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    Re: Don't box your L body subframe, here's why.

    Harry, From a knowledge point I'm glad you welded your suspension, proved it would crack and you didn't crash!!!

    As the L body is semi independent, the U channel is the part that must be able to twist.

    Welding solid prevents it from twisting, and that left the ends vulnerable to cracking as they weren't designed to twist.

    Some folks U bolt flat steel to the U channel to allow some twist, especially if the U bolts are strategically placed.

    EG: Fewer U bolts, spaced farther apart, more twist, many U bolts close together, less/no twist.

    The rear anti roll characteristics can be fine tuned by adding/removing U bolts.

    Same thing might be accomplished with welding the flat stock, many close welds= cracking, fewer welds, further apart, ...

    Due to the design, there are very strong forces acting on the channel that joins the semi independent trailing arms during driving and cornering. The channel needs to be able to twist somewhat, but as mentioned, the twisting can be tuned.

    SHADOW!!!!!

    A while back Rob decided to lighten his rear trailing arm assembly. I cautioned him about these very strong forces acting on the channel, but he assured me his calculations that came from an Engineering background were valid.

    Everyone knows the L body assembly was overbuilt and could be lightened extensively and that's what he did. He might post some pics, but from memory its full of holes!!.


    He later bragged about transporting a few engine blocks and a bunch of other things in his Charger with no ill effects.

    So, in the end, Harry has proven Shadow to be correct, lighten everything up concerning the assembly, allow it to twist, no problem.

    Remove the ability to twist and even the overbuilt stock assembly will crack on each side of the now nontwistable assembly.

    Thanks
    Randy

    PS:
    Anyone know the interchangeability of L body rear suspensions? A guy on another forum has a damaged 1988 Horizon wants to know if a 1983 Horizon rear suspension assembly will fit. He posted it looks similar but not the exact same, and I cant find any info or pics.


    Randy Hicks
    86 GLHS60
    86 GLHS 373 : SOLD, but never forgotten
    89 Turbo Minivan
    83 Turbo Rampage : SOLD
    Edmonton,Alberta,Canada

  11. #31
    Supporting Member II Turbo Mopar Contributor Shadow's Avatar
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    Re: Don't box your L body subframe, here's why.

    Quote Originally Posted by Pat View Post
    That really depends on spring rates, where the weight on the car is and what the cars intended use is.
    Yeah yeah, I posted that way too fast with Not enough info;

    My post was in reference to my own experience with the Charger. The missing info is the Charger has Slowes tubular cross member and DJ's tubular heim joint A-arms. I'm running 350"/lb springs up front and stock shortened springs/ shocks rear. With that combo and my modded rear trailing axle and the addition of the PB 1" rear anti sway bar, the Charger Destroys the handling characteristics of its former self.

    Add to this the fact that I am comparing the Charger With front anti sway bar vs it now Without!

    Robert Mclellan
    http://www.youtube.com/watch?v=wambNdfnu5M
    10.04 @ 143.28mph (144.82 highest mph)
    Worlds fastest 8v MTX Shelby Charger
    Manitoba's Fastest 4cyl!
    8 valve, No Nitrous!
    New clutch combo is the SH!T!

  12. #32
    Supporting Member II Turbo Mopar Contributor Shadow's Avatar
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    Re: Don't box your L body subframe, here's why.

    Quote Originally Posted by GLHS60 View Post

    SHADOW!!!!!

    A while back Rob decided to lighten his rear trailing arm assembly. I cautioned him about these very strong forces acting on the channel, but he assured me his calculations that came from an Engineering background were valid.

    Everyone knows the L body assembly was overbuilt and could be lightened extensively and that's what he did. He might post some pics, but from memory its full of holes!!.


    He later bragged about transporting a few engine blocks and a bunch of other things in his Charger with no ill effects.

    So, in the end, Harry has proven Shadow to be correct, lighten everything up concerning the assembly, allow it to twist, no problem.

    Remove the ability to twist and even the overbuilt stock assembly will crack on each side of the now nontwistable assembly.

    Thanks
    Randy
    Bro, ixnay on the ics pay. Otherwise Someone is bound to have a hit Say it Fay!

    Know what I say!?

    Oh, and by the way;

    That was 4 engine blocks and 3 cranks and a bunch of odds and ends like TQ plate couple of heads ect ect + my wife and myself with luggage for the wknd. + Don't forget the spare/jack and I even think I squeezed and air tank in there.

    Robert Mclellan
    http://www.youtube.com/watch?v=wambNdfnu5M
    10.04 @ 143.28mph (144.82 highest mph)
    Worlds fastest 8v MTX Shelby Charger
    Manitoba's Fastest 4cyl!
    8 valve, No Nitrous!
    New clutch combo is the SH!T!

  13. #33
    Supporting Member II Turbo Mopar Contributor
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    Re: Don't box your L body subframe, here's why.

    This evolved into a great thread.


    Not saying anything new, but on the track with stock GLHS spring rates and anti-sway bars but with Koni coil overs, I found that rear induced oversteer, the rate of rear rotation, was critical to be able to get the front wheels pointed straight, straight down the next straight, as early as possible, so that they were pulling the car and NOT steering it. Rear ride height and tire pressures were key puzzle parts in getting the car to rotate at the right rate, not so fast as to force me to slow the car down on the entries and not so slow as to delay going WOT. Credit to Craig St Pierre who taught me "get the wheels straight before you mat it."
    John Laing

    "The sole condition which is required in order to succeed in centralizing the supreme power in a democratic community, is to love equality, or to get men to believe you love it. Thus the science of despotism, which was once so complex is simplified, and reduced . . . . to a single principle."
    -- Alexis de Tocqueville

    "One of the methods used by statists to destroy capitalism consists in establishing controls that tie a given industry hand and foot, making it unable to solve its problems, then declaring that freedom has failed and stronger controls are necessary."
    --Ayn Rand

    "To evolve, you don't need a Constitution. All you need is a legislature and a ballot box . . . . things will evolve as much as you want. All of these changes can come about democratically; you don't need a Constitution to do that and it's not the function of a Constitution to do that."
    -- Justice Antonin Scalia

  14. #34
    Supporting Member Turbo Mopar Contributor supercrackerbox's Avatar
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    Re: Don't box your L body subframe, here's why.

    Quote Originally Posted by GLHNSLHT2 View Post
    Be careful, that was my exact setup.
    Would you care to elaborate?

  15. #35
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    Re: Don't box your L body subframe, here's why.

    I know this is a slightly older thread but tons of fwd cars used and still use semi-independent rear suspension.

  16. #36
    The moderately moderate moderator Turbo Mopar Staff
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    Re: Don't box your L body subframe, here's why.

    Quote Originally Posted by thedon809 View Post
    I know this is a slightly older thread but tons of fwd cars used and still use semi-independent rear suspension.
    Exactly. They are a twist beam semi-independent design. They are designed to flex. It isn't like someone here discovered it by accident....lol.
    Bryan
    86 GLHS #161, 2016 Impala
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  17. #37
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    Re: Don't box your L body subframe, here's why.

    On my GLHS Omni autocross car, I used 1" rear bar, 1-1/8" front bar....
    the mopar autocross springs with a coil cut off all round. With stock Koni's.
    I adjusted handling with tire pressures and shock adjustment.

    Won a lot of autocrosses!
    Great stuff for great cars! Poly engine mounts and bushings at: http://www.polybushings.com

  18. #38
    Supporting Member Turbo Mopar Contributor supercrackerbox's Avatar
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    Re: Don't box your L body subframe, here's why.

    Quote Originally Posted by Johnny View Post
    On my GLHS Omni autocross car, I used 1" rear bar, 1-1/8" front bar....
    the mopar autocross springs with a coil cut off all round. With stock Koni's.
    I adjusted handling with tire pressures and shock adjustment.

    Won a lot of autocrosses!
    Well I've got that rear bar that I just bought from you, and I'm taking my rear axle in to be powdered this week. I just want to make sure I'm doing the right thing when I cut the stock bar off.

  19. #39
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    Re: Don't box your L body subframe, here's why.

    OR leave it on and see if you like it that way first. You can always take the stock one off if you think the over steer is too much.
    Great stuff for great cars! Poly engine mounts and bushings at: http://www.polybushings.com

  20. #40
    Supporting Member Turbo Mopar Contributor mopar-tech's Avatar
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    Re: Don't box your L body subframe, here's why.

    Quote Originally Posted by GLHNSLHT2 View Post
    LOL. What size PB rear sway bar did you end up with? I put the 1 1/8" on my GLHT and cut the stock bar off. Under 30mph stuff was a lot of fun. Over 30 MPH was dangerous oversteer. It snapped around on my entering a freeway off-ramp when I had to nail the brakes to not hit the car in front who decided to take it 20MPH slower than needed. Thankfully I had the skills to catch it and keep from hitting the light pole.
    I ran into a similar situation with my Reliant-

    Installed the rear control arm from my old '86 Daytona into the car which had been boxed in. Problem being the Reliant is far lighter in the back than a Daytona! On a twisty back road the car would grip... grip... grip..and then.. ROTATE!

    Did a complete 180 degree spin with utter lack of control, car gave no warning at all. Once one tire breaks loose its party over!

    Taught me a good lesson and by the grace of God did not cost me a car or the life of someone coming the other direction.

    Gary


    It is time, buckle up.

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