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Thread: Couple questions about boxing in Lower Control Arms.

  1. #1
    Senior Member Totally 80s's Avatar
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    Couple questions about boxing in Lower Control Arms.

    Does anyone have any photos of their LCA's boxed in? Besides boxing in, re-painting and replacing the ball joints is there anything else that should be done to the LCA's while they are out? Are there any write ups on how to box them in?

    I assume the shocks and springs need to come out to remove the LCA's so if I was going to upgrade my shocks and springs I should do it at the same time as I upgrade my LCA's?

    Thanks for your help!
    Last edited by Totally 80s; 10-16-2019 at 11:35 AM.
    -Alex
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  2. #2
    Guy with a DeLorean Mark D's Avatar
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    I think there is some debate to be had on whether boxing in the LCA's have any actual effect (good or bad).

    Most of the control arm deflection you see in that scary video that's posted somewhere here on the board is the control arm flexing at the inner bushing where the LCA mounts to the frame. The arm itself is probably deflecting some small amount as well, but the vast majority of the motion is the the bushing joint with the arm moving relative to the frame.

    Adding lower control arm supports like these (or the other tubular style being sold here on the board) seems to have a much greater effect at keeping the suspension geometry in the designed location vs flopping all over the place.


    Boxing in the LCA will definitely add some overall strength to the arm, but is that a good thing or a bad thing? Most of the LCA failures I've seen in photos of are right at the ball joint cup or at the inner bushing joint near the frame. Boxing in the LCA with a plate typically does not reinforce these failure prone areas, but rather adds strength to the middle of the LCA. All the stress going into the LCA has to be distributed somehow throughout the arm. If the mid section is no longer flexing then some amount of stress is being redistributed into those more failure prone areas.

    Plus there are potential issues with welding where you can create residual stress and take the heat treatment (if there is any) out of the steel in the heat affected zone of the weld. And it's more difficult to try and get paint (or powdercoat) coverage inside of the enclosed boxed section which may lead to corrosion issues.

    When I restored my suspension I chose not to box in the LCA's and go with the reinforcement/supports instead. If I ever upgrade from the stock LCA's I'd most likely go with the DPI stainless arms since those have actually had some structural analysis and testing done. The billet aluminum arms from DMCMW also seem like a pretty robust option as well.

  3. #3
    LS Swapper Josh's Avatar
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    While mark made some good points, I do think the "outriggers" as i call them are a replacement for boxed LCAs.
    They work together.

    It is very important to re-enforce the area around the ball joint before you consider boxing as well. Furthermore if you are not a competent welder you can do more damage than good on the thin sheetmetal used in the LCAs.

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  4. #4
    Senior Member
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    There is no heat treat on the LCA's, they are just pressed cold rolled sheet metal. What you should be concerned about is warping or otherwise distorting the control arm from the welding. That can be handled but it takes some care to avoid any distortion.
    David Teitelbaum

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