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Thread: Rear bumper brackets

  1. #1
    Registered User tanny's Avatar
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    Question Rear bumper brackets

    Hopefully I can describe the problem well enough to get an answer. The rear bumper on my 73 z has been tweaked a bit, so I removed it. Both brackets(the rear ones, not the side brackets) seem to be bent, but I'm not sure how much. Are undamaged brackets formed with only right angles, or are the bends in the bracket something other than 90 degree bends? Are they supposed to be exactly rectangular in overall shape, or are they more trapezoidal with angled legs(sides)? The reason it's not clear to me is that the bumper when mounted is not that far out of alignment(is shifted slightly to drivers side), both brackets have similar shapes, and I've never seen brackets on an undamaged bumper to compare them to. Also, is silver POR 15 good idea for painting inside the bumper where plenty of rust has accumulated in spots? Thanks, Victor.

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    Registered User Marty Rogan's Avatar
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    Default POR 15

    Hi Victor,

    I have a 70 now, my 73 has been gone since 1987, so I can't really help you on what the 73 mounts look like.

    When I put new bumpers on my car last year, I used POR 15 silver on the backsides. It turned out really nice. No more rust on these expensive bumpers!

    I would recommend you try to get all of the existing rust off the bumpers first. Then treat it with their Metal Prep.

    Good luck!

    Marty

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    Supporting Member EScanlon's Avatar
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    Default

    Rejgarding Silver POR on the backside of the bumper:

    Excellent idea, that's what I did. Let's face it, you need to protect the area, yolu need the rust preventative paint to stick and you want it to somewhat look correct for the part......Silver POR fits the bill exactly.

    Follow the instructions for applying POR and you're set.

    Regarding the bumper brackets.

    When I had mine off to rework the rear valance, I noticed that one of the legs was longer than the other, but could not discern a difference from one piece to the other. When I replaced them, I put them on the bumper FIRST, and then noticed that it was imperative that the longer leg go on the INSIDE bolts, so that the back part of the bumper mounting bracket would be flat to the body. There is a small amount of play on the bolt holes in the bracket both to the bumper and to the body.

    When you mount the brackets to the bumper, leave the nuts slightly loose so that you can still shift the bumper if necessary.

    There are a couple ways that I've seen folks mount the rear bumper. I've seen it mounted as one piece, even though that makes it trickier, and I've also seen it mounted as 3 pieces.

    The key to the installation is to ensure that the distance from the body to the bumper is even to corresponding matching symmetry points. What that means is that you measure the gap at the same point on each side.

    Hope this helps.
    Enrique Scanlon

  4. #4
    Registered User tanny's Avatar
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    Thanks for all the replies,

    I'll try installing the bumper in one piece because I should then be able to see how to bend the brackets back to where the bumper will line up properly and also because I can't remove the the small bolts that retain the rubber trim(rusted too much to remove without breaking). Another question: is sand blasting the only effective way to get the rust off the inside of the bumper, or will something like naval jelly work on fairly thick rust?

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    Supporting Member EScanlon's Avatar
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    If you have access to a sandblaster I would recommend that method as opposed to a chemical rust converter. I have only used Naval Jelly one time and I can't recall being pleased with the results with it.

    The sandblaster WILL remove the rust, unfortunately it REMOVES the material. If extremely rusty, to the point of thinning out the metal to aluminum foil stage, you might blast a hole in it. If that's the case, the metal is gone and needs replacing anyway.

    Naval Jelly, if I recall properly, uses chemicals to "convert" FeO to something else by either removing the Oxygen or adding something to it. I can't imagine the chemical converters being able to penetrate thick rust deep enough to "kill" it.

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  6. #6
    Registered User tanny's Avatar
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    I think you're right about the naval jelly, I think it probably only works on thin surface rust. I used a small grinder and a dremel today and it worked fine on the accessible rust. I may pour some naval jelly into the recesses I can't reach with the tools, then give it the POR 15 treatment. Seems to be plenty of good metal left. Thanks, Victor.

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