Hood flex in rear

[grc53]

Never restored a 53 chevy truck and would like to know if the "buckle in the rear of my hood is common for these trucks

[1952]

seems a bit much...heat up the area with a torch and tighten up the metal

[MARTINSR]

I wouldn't heat it with a torch, their is likely a buckle ahead of that spot right over the brace, those hoods are very weak there and that is what commonly happens.

“Basics of Basics” Flat panel repair
By Brian Martin

When you have a large flat panel that is flexing the first thing you need to do is find out why. Sometimes you can stop it, other times you can’t. But if you can stop it, you’ll have a much easier time with the body filler work. Hoods, decklids, and the roof are particularly difficult because the heat and weight of the plastic filler can have an effect on the metal. The good news is many times it is very easy to repair.

First off, there is no such thing as a “flat” panel. All panels that appear flat actually have a slight crown or gentle bow up in the middle. Go to a flat panel and lay a straight edge across it. You will see that the straight edge in not touching the panel at the on the outer ends. If the panel were perfectly flat it would appear to the eye to be concave. It would also have no “body” and flex very easily. This is the problem with your large flexing panel; it has “lost” its crown and is now weak and flexible.

The first place to start your search for a culprit is under the panel. Many panels have inner structure that supports the outer skin. When the outer panel has been damaged the inner structure was bent down along with the outer. This inner structure can be in the form of just a simple inch or so wide support running across the panel to the complete support by a stamped panel that goes covers the underside of the panel. These full inner structures can commonly be found on hoods and decklids. The inner structure can sometimes be bent down, causing your flexing. It usually is very close to the outer skin, with just a thin layer of a foam or urethane adhesive. It may have small “dollops” of this foam or adhesive that has been squished between the inner structure and outer skin or even a thin piece of tarpaper.

You can push up on these low spots to return it to supporting the outer skin, as it should. But it is difficult because you can’t push it past where it needs to be. On this particular type of damage, the inner structure would need to go past the correct shape and then “relax” back down to where it belongs. It can’t do this of course because the outer panel is there and limits the inner structure from going up where it needs to go. Just as with looking at the “big picture” when you look at any dent, you need to search for a kink or bend that is holding the inner structure down in that area. If you apply pressure up on the low area and tap out these kinks, you may get it to stay back in shape. If these methods don’t get it back up to support the outer panel properly, you will need to “shim” between the two panels to get the outer panel up where it belongs. This can be done with sheet of tarpaper or more adhesive. As a last resort a thin piece of wood like a paint stirring stick can be used. Of course, this is a little on the funky side but if you are haven’t been able to correct the problem, something has to be done. What you have to watch out for is applying too much pressure in one area. If you were to force a piece of wood in there, you will likely be making a high spot on the outside. That would just give you in a whole new problem.

Sight down the body lines that are nearest the low, “oil canning” , or just plain flexing area. A body line is effectively the “edge” of the panel. Those crowns in the flat panel that I mention end at the body line. So each area in between the lines is sort of like an individual panel. Look to see if the body line is low, it may be holding down your panel. If it is, you need to push it up. To help you determine how straight the line is sometimes you can use a metal ruler as a “straight edge”. How can this be done on a crowned panel you ask? A metal carpenters yard stick will bend very easily, right? So what you do is lay the yard stick on it’s back against the panel and apply a little pressure on the outward edges low area where the metal is OK. You will then have a “curved straight edge”. I have a drawer with a number of these metal or aluminum rulers in it and find them very useful. I treat them like rice paper and they will last a lifetime.

So lets say that you have found that you have no low spots in the body lines or there were one or two and you repaired them. Now you have to look for something else that is holding the panel down. This can usually be found in the form of a “crown” or “brow”. When you put a dent in any panel the metal has to “go” somewhere. All panels have this crown, right? So as an example picture a metal rod that is 3 feet long. This rod has a slight bend to it. The center of the rod is up from the ends about three inches. If you were to push down on the center, the rod would get “longer”, right? So, if the ends of the rod were clamped in vices, the “extra” rod would force the areas on the sides of where you were pushing to go up. You panel does the same thing only on a much smaller scale. Most brows will be found on the outer edges of a panel, this includes of course at the edge of the body line. They are VERY common around the outer edges of a roof. Search around the outer edges of ANY bent roof and you will find them.

The brow or crown is a U, C, L or even I shaped high spot. In the center of that curved high spot is a low spot, sort of like a “pocket” in the brow. Just one or two of these will make a panel, especially a large panel look like a cotton sheet! What you have to do is to push up on that low spot while tapping down on the brow. When I say “tap” I mean TAP. Just the weight of the hammer bouncing off the brow will do it sometimes. Use a large VERY flat body hammer or a flat body spoon for this repair. If you are careful you can repair these brows with little to no plastic filler. Just take you time and keep checking the area with a block with sand paper or a vexon file if you have one for low and high spots.

Now, if you simply can eliminate the brow and low spot, you have won the battle. If it takes some plastic filler, so be it, you have given the panel it’s strength back and that is what matters.

[MARTINSR]

Let me make it clear, you want to lift up that rear a little bit while you "massage" the brown down. Run your hand with it lightly laying flat on the panel going front to rear on the hood just in the area over that brace and you will feel that brow. And remember, if you remove that brow (lightly, you don't want to thin the metal beating on it) and the end of the hood is still "loose" and hanging a little, it won't matter on the truck because it rests on the rear hood seal that is on the cowl, so it's not a big deal.

Just don't hit it with a dolly under it, this is called "on dolly" and it stretches the metal by making it thinner, don't do that.

Just remember that there is a HUGE chance that area isn't what is bad, it is simply REACTING to something near it....a brow.

Brian

[dwcsr]

Yes that's pretty common, after doing a lot of these hoods, let me give you my advice. Leave it alone till you have test fitted it to the cab WITH the anti squeak rubber in place along with the hood bumpers and hood adjusted properly. You may see that it lays flat when closed or if not you can turn that edge up by hand with very little effort so it looks good and fits nice.

Trying to stretch it or shrink or dolly it out it if you have no experience will most always make the hood unrepairable. It will most certainly make it wavy in that spot and that will show far more than a little down turn.

I've seen hoods worse than that lay flat when closed when installed and adjusted properly.

[MARTINSR]

Originally Posted by dwcsr

Yes that's pretty common, after doing a lot of these hoods, let me give you my advice. Leave it alone till you have test fitted it to the cab WITH the anti squeak rubber in place along with the hood bumpers and hood adjusted properly. You may see that it lays flat when closed or if not you can turn that edge up by hand with very little effort so it looks good and fits nice.

Trying to stretch it or shrink or dolly it out it if you have no experience will most always make the hood unrepairable. It will most certainly make it wavy in that spot and that will show far more than a little down turn.

I've seen hoods worse than that lay flat when closed when installed and adjusted properly.

VERY GOOD ADVICE! OMG, VERY GOOD ADVICE!

grc53, Listen to this advice, hope you see it before you go out there with mine! You do this FIRST and if there is a brow you can take care of it. But this is a very, VERY difficult area on these hoods. It's an odd spot unlike any hood on any car made in that era or later, it's very odd. That metal is "loose" without any support and it will often seem odd just because there is no other car or truck like that so you may think it's worse than it really is.

Don't touch it until you have trial fit it!

Brian

[grc53]

Thanks for the advice!!!! I think the first step is to put it back on the truck and check the fit. If it is ok, then I think I will let it go as it is. If it is not okay and I think something needs to be done, I will do some further analysis and post some pictures before I do any thing. I will not get a chance to do that for a few days.

[MARTINSR]

That area is very very touchy! It can get screwed up worse VERY easily so I am glad you saw dwcsr's advice before you did what I said. What I said is AFTER you have looked it over good on the truck as dwcsr advised.

Brian

[joedoh]

the rear passenger side of my 47 hood waved around and wiggled while driving, it was pretty distracting. I put a dab of silicone between the brace and the skin and no more wiggle. there are better ways to do it correctly for sure, but it only took about 10 seconds to do and 8 hours for the silicone to dry completely.

[MARTINSR]

Bringing the back of the hood down to fit the rubber should do it too. If the metal is flexing out over the brace and not at the back, that silicone is a perfectly fine repair.

Brian

[joedoh]

I should add that before I added the silicone the rear of the hood stuck up about 3/8" over the cowl. I put the dab of silicone on the brace and something heavy on the hood and its still stuck.

[grc53]

Thanks to everyone for the advice. I placed the hood on the truck and the rub strip brought the bow in the rear right up to were it should be. That's a new one on me. I have restore for 40 years and have never seen this type of fit , though this is my first chevy truck. Your advice kept me from making a big mistake.

[dwcsr]

You may see a wide V shaped wrinkle in it once its painted so I would try to get some shin on it and then re test fit and look out over the hood. I think that happens when guys pick them up and its up side down. I can't see that naturally happening when its on the truck

[grc53]

Dwsr, could explain where the v and wrinkle would be

[MARTINSR]

It's the buckle or kink I refer to in the "Basics of Basics" I posted. It would be in the front of the low spot over the top of that brace that goes under the hood.

Most any dent has one to some degree, large flat panels will have them about every time when there is a dent. On this roof it's at each side and in the front and in the back.



That's why I suggested you run you hand flat a foot or so in front of the back edge of the hood going forward over that brace. If there is a kink there you should feel it.


Brian

[grc53]

I don't feel anything in front of the brace. There is a small indentation in the center of the hood where the two pieces come together. It involves both sides and is located where there is a hole. I assume the hole is there to mount the center hood molding. The indentation is less than 2 inches on each side and is no deeper than 1/8 inch. It does not seem that this would cause a buckle.

[dwcsr]

you may not have had the metal go beyond its flex point and set so you may never see the wrinkle. MartinSR example has gone beyond the metals flex point and set to a kink in the panel. I think its an exaggerated form of what I see when the hood is down in that area but similar in idea.

That dip in the center another common problem is often fixed with a pole on the ground up to that point that's has the dip. With the hood bolted in position , push the hood down gently on the pole till it smooth's out. Go easy you don't want to reverse the dip and make it a hump.

[MARTINSR]

I hope I didn't cause confusion I used an exaggerated version, I posted that photo so it would be clear as to what it is. On your hood it would be tiny. Feeling it is often not every easy without experience on something like that hood. It could be very subtle.

Brian