Bodywork welding precautions

Discussion in 'Bodywork' started by rigel, Jul 7, 2011.

  1. rigel

    rigel Active Member

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    Greetings all,

    I’m sure I’ve read on another thread (that I now can't find), that when welding on a car, (mines a W124) certain precautions should be taken so as not to damage some of the more delicate electrical components.

    Can anyone please enlighten me as to what precautions I should be checking to see are done, when my car goes to have a little welding done?

    Regards.
     
  2. 312 Sprinter

    312 Sprinter Active Member

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  3. OP
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    rigel

    rigel Active Member

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    thanks for that Sprinter,

    knew i'd read it somewhere before. loved reading your thread the first time, hopefully will be revisiting it again this evening.

    regards.
     
  4. Sp!ke

    Sp!ke Administrator

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    Shouldnt one also normally disconnect the negative lead of the battery?
     
  5. grober

    grober MB Master

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    IT REALLY DEPENDS ON HOW " RISK AVERSE" YOU ARE? I would be inclined to remove any control units in close proximity to any welding. For example if welding towards the rear of the car I would be inclined to remove the convenience control unit and any units associated with control of the roof/ rollover bar. Here's a link to a PDF of most of their locations. http://w124-zone.com/downloads/MB CD/W124/w124CD1/Program/ETM/relay_control.pdf
     
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    rigel

    rigel Active Member

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    thanks for that grober, its going to take some digesting.

    do you have the same sort of documentation showing the drain hole positions? and how and where the water is supposed to flow through the car?

    have found the main 6 plugs (four on the floor pan and two in the boot), but i'm sure ive read somewher that there are up to 12.:dk:

    regards.
     
  7. nick.ged

    nick.ged Active Member

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    I have welded many cars, both modern and classic.

    I always disconnect both battery connections, and have never had any issues with any modulus, ecus' ect.

    I did however, also disconnect my megasquirt when I welded the sills on the widebody, just in case.
     
  8. kth286

    kth286 MB Enthusiast

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    I would definately be taking the battery cables off and totally disconnecting and removing the £1200 main ECU.
     
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    rigel

    rigel Active Member

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    Thanks for the information, is this a tricky manoeuvre?

    The guy who is going to do the welding is a good bodywork welder, but he normally works on Jaguars, so am not sure how familiar he will be with removing the ECU on a W124.

    Regards.
     
  10. grober

    grober MB Master

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    If you print out that PDF I gave you that should help. Basically together with the ABS controller the main ECU IS behind the flexible black plastic shield behind the battery. Its best to remove the battery w[ which you will be disconnecting anyway] - you can place the bonnet in the fully upright position to facilitate this----- then its just a question of carefully removing some large connectors 2 on the ABS unit and one large one on the engine ECU irrc then removing the rectangular shaped units. Can I ask again where he is going to be welding?
     
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  11. Dee-124CAB

    Dee-124CAB MB Enthusiast

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    Does the OVP relay not protect against this very type of thing?
     
  12. grober

    grober MB Master

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    Against induced RF generated by a welding arc-- nope! Its really designed to protect against DC VOLTAGE surges
     
  13. OP
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    rigel

    rigel Active Member

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    Thanks again for that Graeme,

    1. Rear N/S wheel arch front bit of the wheel house, there is a small rust patch around the grommet that looks forward into the window cavity.
    2. front N/S wheel arch, one of the studs that hold the wheel lining up has rusted through.
    3. under the windscreen washer bottle.

    From what I can gather after reading through other threads, nothing too out of the usual.

    Will try and load some pictures when the work is done.
     
  14. grober

    grober MB Master

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    The only unit in close proximity to the rear N/S wheel arch welding would be the N57 convenience module under the rear seat squab. Easy to get at just push the small red clip on the seat base and raise the seat base up and forwards.Its under the sound deadening mat. The other locations are a reasonable distance away from critical components.
     
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