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  #1  
Old 02-14-2003, 12:38 PM
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what do I disconnect when welding

The hood of my 1989 230E is self opening while driving like when I open it from inside the car. I found 2 bolts holding the top side of the lock (see picture). They are screwed under the hood and 1 of them is getting loose because the base of the bolt has a crack where the bolt is screwed and needs welding.
I need to know what do I need to disconnect when using electrical welding. I don't wat to cause problem to microchips of the car.
Thanks.

Hurshi
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what do I disconnect when welding-hood-problem.jpg  
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1989 230E, 8v, 166.000 km, updated to 94/95 trunk & hood
2002 Daewoo Nexia 50.000 km
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Last edited by Hurshi; 02-14-2003 at 12:50 PM.
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Old 02-14-2003, 12:54 PM
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Most people don't disconnect anything. I always disconnect the ground at the battery, but I don't think that is even necessary. Are you going to MIG weld it? Be careful with the heat and your hood. You may want to fix a wet towel to the top of your hood while welding to absorb heat and stitch weld depending on the clearance ( I can't tell from the pic) It would be easier to braze it if the area can take the heat.
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Old 02-14-2003, 01:06 PM
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Ahem,,,, if I were you I would disconnect BOTH the positive and the negative. We always do that when we weld on any car. I've heard of airbags blowing, computers getting screwed up and all kinds of interesting stuff. It's cheap insurance, believe me.:p
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Old 02-14-2003, 01:32 PM
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It's also important to ground as close as possible to where you're working so you have a short path.

PJG56: You're right. You may as well do both if you're doing one. Have you ever heard of clamping the negative and positive leads together after disconnecting them from the battery? I know some places do this as well but don't know why.
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Old 02-14-2003, 03:13 PM
moedip
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Strange things can happen to electronics when welding. Shorting the positive battery cable to ground (joining the negative and positive terminals) puts all circuits at ground potential and eliminates the possibility of a ground loop circuit which can generate voltages higher than 12v in the different circuits. I always short the two battery positive /negatives leads together before welding. Have had no problem since doing that. Prior to doing it - I blew the voltage stabilizer on a VW - even though the positive cable was disconnected from the battery. For the time it takes - it's worth it. The other suggestion of keeping the welding ground close to the welding point is a MUST to keep stray currents from running through the body of the car.
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Old 02-14-2003, 03:44 PM
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Thanks moedip! I will adopt that method myself as that makes perfect sense.
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Old 02-15-2003, 12:14 AM
1992300e
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Great advice

Thanks for the great advice. I do my own welding too. I would second the motion regarding heat. Welding builds big heat quickly and you need to be careful that you don't warp or set anything near the weld on fire.

good luck,
Joel
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Old 02-16-2003, 06:02 AM
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Using all the advices I was able to weld the hood with no problems. Thanks to everybody.
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1989 230E, 8v, 166.000 km, updated to 94/95 trunk & hood
2002 Daewoo Nexia 50.000 km
Sold:
1987 VW Jetta GLE 16V, Recaro seats
1982 Volvo 240 DL (lovely car!)
and few more american cars.
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Old 02-16-2003, 08:45 AM
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Hurshi:
That's great. I wanted to thank you for posting your results. So many of these threads have great material and information, but the initial poster seldom posts the results or resolution of the problem. Good job.
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