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I have removed the rear quarter and am looking for root causes of why rust began to develop in the "classic" locations.

Just in front of the the wheel well, and just aft of the door jamb, there is a rust hole. This is where the rust builds up that adds to the corrosion that causes the dome lights to go out.

Now that the panel is off, i have a clear view of the relative area. In the bottom of the body support pieces, there is a hole about 1" in diameter. However, there is a rubber grommet blocking it. I would think the grommet was initially placed there to keep water from getting up into this enclosed space. HOwever, doesn't it being there prevent drainage of water?

I am thiking i should remove the rubber grommet to promote drainiage of water.

thoughts.
mj
 

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I am not an expert, but my guess would be that the grommet would be there to prevent water, and foreign debris (mud, rocks etc) from getting trapped in there, and causing rust. I would opt for drilling a hole into the grommet, instead of taking it out.
 

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I think the rust is caused more by the buildup of dirt that absorbs water than water alone being retained in the panels. I know I pulled about 15 to 20 pounds of dirt-road dust out of both of my rear quarters when I started cutting the fenders for bigger tires. Your biggest enemy is simple dust and dirt, just making sure the water drains won't solve the problem.
 

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4 items are needed for corrosion to take place; anode, cathode, electrolyte and a path for electron flow. 2 dissimilar metals provide the anode and cathode, the moisture mixed with salt/minerals (found in the dirt) create the electrolyte and when the 2 metals in contact with each they provide for the electron flow. When all 4 come together in a circular fashion it creates an electrical circuit. The result is the anode will start to corrode. By removing the moisture, one of the dissimilar metals or if you keep the metals from contacting each other you will stop the corrosion. With a trail and mud rig the best thing you can do is wash the dirt out of all of the cracks as often as possible otherwise the dirt will absorb the humidity in the air and cause corrosion/rust.

I washed my trucks and bronco once every 6 months when I lived in the dry deserts of AZ and NV and I have never had rust problems until I moved to the wet state TX.

In summary you have 2 options:
1. wash (remove electrolyte), dry (remove electrolyte) and wax (a barrier to the electrolyte) every square inch and every nook and cranny of or Bronco after every ride or
2. replace all of the metal with fiberglass.
 

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Discussion Starter #6
wow thanks johnorama.

So, why would there be a drain hole there, if it is plugged from the factory.

If it is suposed to keep out dirt, then why even place a hole there and later fill it with a grommet?
mj
 

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who knows why it is there? Maybe a hole was needed for the assembly process, painting, tool access. Maybe it is an optional hole; keep it plugged for highway or remove it for swamp crossing.

If you have an original or "after market" drain hole, dont count on it not being plugged, it might get clogged and hold all the stuff that makes metal rust. A check valve would be sweet, if it were possible.
 

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a drain hole usually has a plug in it to keep stuff out.

Our vehicles aren't necessarily built to see some of the things we do to them. Water crossings, axle deep in mud, things of that nature. They're purely capable of it, but it wasn't necessarily in design specs when it was on the drawing board.
 

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the 92-94 explorers have a tube to drain water from the roof into the rocker panel. but there is no drain hole in the rocker panel. so the rockers rot out but the roof doesnt. later model broncos dont have the mystery plug.
 
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