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Old 04-09-2018, 10:22 AM
StingRay StingRay is offline
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Default 69-72 GM truck hood

I have a 69-72 GM truck hood that has a dip in the middle. This is pretty common but I've never seen anybody actually address a repair of this condition. On the pass side of the rib that runs front to back it actually has a dip. This is the area in the circle. On the drivers it's lost it's crown in the same area but isn't concave. The rib itself is fairly flat in the middle section where I'd expect it to have a small crown. I have a few theories but am frankly scared to test them out. It's a very low crown panel and one wrong move it will be scrap.

There are supports that run front to back either side of the center rib. they typically have foam between them and the skin. I've tried a few different shims to see what difference is made. Shims stiffen the hood but do not change the condition of the hood.

I'm thinking that over time the hood fluttering up and down in the middle at the rib (and they do flutter) could have any or all of the following conditions. Stretched material at the bottom of the rib as though a hat channel had it's lower flanges stretched. The rib could have over time sagged and pushed the front and rear of the hood out like a sagged roof truss. This would create a false stretch situation. The rib could have flattened out sideways pushing material on the hood side to side a little also creating a false stretch. While possible I don't see the area that is concave as actually being stretched itself and am leaning towards it being a false stretch because of another condition.

I'm hoping some of the vast experience here has had to deal with a scenario like this before and can give me some advice. It's a pretty nice hood as these go and I'd like to make it perfect. The funny color of the hood in the pics is because it has been metal prepped and there is zinc phosphate on the surface.

IMG_5357.jpg

IMG_5356.jpg

IMG_5355.jpg

IMG_5354.jpg
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Last edited by Steve Hamilton; 04-12-2018 at 02:17 PM.
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Old 04-12-2018, 11:22 AM
StingRay StingRay is offline
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Wow. 220 views and nobody has any thoughts on this kind of issue. Some of you guys that build whole cars have got to have an idea on this. It's such a low crown minimally supported piece that I know enough to know that there are smarter people than me that have tackled stuff like this before. I'd rather learn from your mistakes than mine. LOL.
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Old 04-12-2018, 04:15 PM
steve.murphy steve.murphy is offline
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Hi Ray,
Can we see some photos of the back side of the hood so we can see the bracing support?
Thanks
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Old 04-12-2018, 05:17 PM
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Steve Hamilton Steve Hamilton is offline
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Hi Ray
The rib on that hood is most of the strength.
Any lack of crown to the sheet on either side of the rib is secondary damage. The rib was overloaded to the point that it deformed. Now the low crown areas are not supported correctly which allows them to oil can.
I would flip the hood upside down, and support it around the edge, so the rib and low crown are not touching. Allow some space below them for the metal flex and for you to place toolset needed.
Get or make a wooden chisel out of hard wood. Shape it at the contact point so that it matches the shape of the creases on the inside of the rib. Kinda like a cold chisel but make it 2 1/2 to 3 inches across. Give it a slight crown from end to end and radius the corners to avoid tool marking.
I would use a ball been or dead blow hammer of about 1 pound. A normal body hammer will not be heavy enough.
Use the straight edge to find where the rib is bent. Work the crease at each side of the rib. A few inches either side of the most damaged area. Slide the chisel along as you strike it, liter strikes at the ends and heavier in the middle.

Go easy at first and check your results. If it isn’t moving then swing a little harder.
When you get the proper crown back in the rib I think the low crown areas will be strong again,

Steve
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Old 04-12-2018, 06:22 PM
Charlie Myres Charlie Myres is offline
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Steve's plan sounds like a winner to me.

What about supporting the panel on sandbags, to do as Steve suggests?
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Old 04-13-2018, 06:26 AM
Gojeep Gojeep is offline
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Don't know if it is of any help but how I tackled the same problem on my build.
http://www.allmetalshaping.com/showt...=12411&page=38
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Old 04-16-2018, 09:19 AM
StingRay StingRay is offline
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Thanks for the input guys.You've pretty much confirmed what I believed. I cut a piece of 3/4 Fir plywood with an arc of about 1/8" over 33" I set the hood on it at the rib. I used some different diameters of pipe up against the radius side of the rib with a dead blow hammer to work the rib a bit. This pulled the material in a bit and put a bit of crown back in the rib. I increased the radius of the wooden rib a couple times as I worked through it. This got the surrounding metal back to no dip. Then while still on the wooden rib I used a light slapper from the bottom on the area next to the rib to help rearrange the metal a bit. This brought the lowest area on the pass side up a little more. I washed over the area afterwards very lightly with a shrinking disc. I just got it hot enough to steam a little bit. Didn't even get color. I had a number of small dings to clean up and a couple were inaccessible from the back side as the there is extensive inner structure at the front and back. I used the Unispotter to pull those. I use very short burst on the trigger so the pins will come off clean and minimize any hardening. . I'll get some primer on it and glue the new foam back in under the supports. I'm pretty happy with the results but this noodle is going to be ugly to block sand. I'll need a sanding block with a hover feature.
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File Type: jpg IMG_5361.jpg (79.0 KB, 40 views)
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Last edited by StingRay; 04-16-2018 at 09:23 AM.
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