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Thread: How to best repair mercedes inner wheel well

  1. #1
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    Default How to best repair mercedes inner wheel well

    Hi there all. My first post here but I happened upon the forum searching rust repair and it has given me some superb insights into repairing rust and corrosion.

    I set about cleaning the inner arches on my 2004 mercedes cl500 and ended up with a hole at the top near the strut tower as shown in the pics. My plan is to from the top grind around the hole and cut some back to good metal first. I have now bought a welder so plan on welding a patch onto the top to cover it as I'm not confident in butt welding a piece in. So cut a square piece of maybe 1.2mm sheet metal tack it hammer down into shape and work round till to shape and all welded in.

    I was going to use weld through primer on the backside of the repair piece to protect it then grind down welds and some paint over the top.

    Then on the underside which will get the water and crud from the wheels use rust encapsulated then some chassis protection paint to protect that side.

    My question is am I on the right path here? If so any ore tips or advice that you can offer as well? Thanks in advance for any help.IMG20220129162713.jpgIMG20220129162616.jpgIMG20220129162713.jpgIMG20220129162616.jpg

  2. #2
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    You are going to have to shape and weld in a patch panel that extends into good solid metal. I'm curious on how you got a rust spot up this high? Was this eaten by an acid product maybe? Very confusing. Not a hard fix if you have any experience with sheet metal or aluminum.

  3. #3
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    Thanks that's the plan and hopefully good metal is close by.

    Would a lap weld be ok?

    The rust is so high up as there is a plastic holder part with a foam pad on the bottom that the coolant lines run through that sits directly on top of where the hole is. I assume water got in the drain hole and would wet the foam then it would just rot the metal underneath.

    I'm also unsure why the images have doubled as only appear to be attached once.

  4. #4
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    Be sure to clean it up underneath and use a good epoxy primer and sealer on the underside after the patch is in place.

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    Quote Originally Posted by Kbald View Post
    Thanks that's the plan and hopefully good metal is close by.

    Would a lap weld be ok?

    The rust is so high up as there is a plastic holder part with a foam pad on the bottom that the coolant lines run through that sits directly on top of where the hole is. I assume water got in the drain hole and would wet the foam then it would just rot the metal underneath.

    I'm also unsure why the images have doubled as only appear to be attached once.
    Are you referring to a lap joint weld or a "backer" plate weld? Either will work but a lap joint using a bead roller looks cleaner. As Len stated make sure you can clean out to good metal and prime

  6. #6
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    Thanks all for your replies.

    I thought I meant lap weld but I'm new to all this. Essentially what I mean is weld a piece on top of the cut out hole rather than make a piece to fit in the hole exactly if that makes sense.

    I used the aluminium tape and fibre glass filer learnt on here on some other small holes which worked well but think welding here would be best.

  7. #7
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    Quote Originally Posted by Kbald View Post
    Thanks all for your replies.

    I thought I meant lap weld but I'm new to all this. Essentially what I mean is weld a piece on top of the cut out hole rather than make a piece to fit in the hole exactly if that makes sense.

    I used the aluminium tape and fibre glass filer learnt on here on some other small holes which worked well but think welding here would be best.
    Yes that will work, just be sure and use a weld through primer and seal the underside. The fiber filler may work for a while but I would think the movement and flexing from the shock tower is going to to eventually break the filler out.

  8. #8
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    Perfect thanks that sounds like the plan. Just need to build up the courage now to execute it which I will do.

  9. #9
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    Quote Originally Posted by Kbald View Post
    Thanks all for your replies.

    I thought I meant lap weld but I'm new to all this. Essentially what I mean is weld a piece on top of the cut out hole rather than make a piece to fit in the hole exactly if that makes sense.

    I used the aluminium tape and fibre glass filer learnt on here on some other small holes which worked well but think welding here would be best.
    A small tube of metal bonding adhesive may also work if you don't want to weld. It cost about $30 a tube plus the cost of the caulk gun conversion kit which is $8.50. The manufacture (Fusor) explains it below.


    Substrates: Installation and bonding of unprimed metals including aluminum Applications: Secondary panel bonding of quarter panels, rear body panels, roof panels and door skins, and replacing rivets or mechanical fasteners
    Provides excellent corrosion protection
    Designed to create uniform bondline thickness despite differences in clamping techniques
    Built-in color indicator; turns from beige to green as adhesive cures
    Meets or exceeds the DaimlerChrysler weld-bonding specification

  10. #10
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    Thanks I've bought a welder to use so just need to practice on some scrap first get used to it then use it on the car. Always a bit daunting doing things for the first time but once you've got the skills they always come in handy.

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    Quote Originally Posted by Kbald View Post
    Thanks I've bought a welder to use so just need to practice on some scrap first get used to it then use it on the car. Always a bit daunting doing things for the first time but once you've got the skills they always come in handy.
    Being your first time with a welder and I suspect you haven't made too many patch panels, don't be afraid of making this a multi plate repair as opposed to trying to get it correct in one shot. I highly recommend you pick up a set of cleco fasteners, they will really aid this and future repair projects.

  12. #12
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    Here are a few examples of what I use
    Attached Images Attached Images

  13. #13
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    I used to use small sheet metal screws on lap joints, but clekos are quicker to remove and reinstall - and the hole/threads won't wear and get a little loose like they can with screws. I bought a bunch of cleckos from a airplane tool supply company, but I always find it doesn't take very many to do the job.

    I have a bunch of those butt panel clamps too. I find those tend to space the joint out just a little further than I like - but they work great when you want to align for a butt weld.

  14. #14
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    being so close to the shock tower you'll want to be certain your repair is sound. it was mentioned there will be flexing and that's so true, you wouldn't believe how much stress there is in that area.
    if you want it (the repair) invisible, consider putting the patch panel in from underneath. it's easier to fill and blend that way. if it's just a driver and you're just trying to hold off the rust for as long as you can, work it from on top. then you can tap it down as you weld your way around it.
    i feel like the damage goes further than you think. the rust looks like it came from underneath. salt being thrown from the front tire?
    b marler

  15. #15
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    Quote Originally Posted by Ronf View Post
    Being your first time with a welder and I suspect you haven't made too many patch panels, don't be afraid of making this a multi plate repair as opposed to trying to get it correct in one shot. I highly recommend you pick up a set of cleco fasteners, they will really aid this and future repair projects.
    do this. small repair sections are easier to fit and handle. you can use a clamp through the hole to tighten up the mating surfaces that way. sure it's more welding, but not that much.
    whatever you do, be sure to go get a couple of welding blankets. drape them over the car so you only leave the repair section exposed. (like a surgeon does in the operating room.) weld blankets are cheap, no excuse to not have them. they help you not catch everything on fire. little smoldering bits can burst into flame hours after you left the area.
    b marler

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