gbledsoe3

For all those with more experience than I, are these "cracks" normal or should I weld them shut? Not the big slot but the lines on either side. This is under the hood on a 71 Supreme. I realize the slots are for collision protection to allow the hood to fold up on itself and not come through the windshield and decapitate the front seat occupants.

70Post

Those are not uncommon....have seen that before. Slight flexing over time and the bottom of the slot is where the flexing force concentrates and eventually the crack occurs. Last time was a few years back on a '72 442 OAI hood. You can tack the area with a welder, grind down welds, etc to as much detail as you like.....that's what I did. It's easy to burn through since you are near a thin edge of metal but it can be done.

gbledsoe3

Thanks, I'll be sure to tack those and clean up after I get all the sheet metal hung and align d.

MDchanic

Yes, that's a common failure point. If not treated well, those can get a lot worse.

In my experience, the GM hood is just a little bit too weak for the GM hood hinges, and when closing the hood, requires a bit of a left-right movement to start, rather than just slamming it straight down.
Over the years, if you don't do that, and you just "brute force" it, this will happen.

- Eric

gbledsoe3

I have another "under hood" question. I'm finishing the underside. Should I replace these "adhesive" spots with something newer? If so, what do you recommend?

MDchanic

I guarantee there's some sort of a 3M body caulk or cushioning product that is just right for that, but I don't know what it is.

If you do not fill those back in, you will likely get rattles or drumming.

- Eric

gbledsoe3

I figured as such and planned on using something. The original ones are dried up and crumbling off as it is.

ELY442

Dont forget to lubricate the hood hinges pivot points.

gbledsoe3

Will do. If my son comes over today and I get the underside cleaned up, plan to hang the hood to start gapping all the body panels.

Although I just received my new rear window and will then start flush mounting it like I did on the front windshield. That'll take a couple weeks of metal work.

marxjunk

its work hardened...they will grow, and can crack again next to the weld..ive fixed 100s over the years...yes 100s...happens all the time..i put a small piece behind it and when i weld i make sure i get all 3 with penetration..helps..but really, keeping the hinges lubed and free, works just as well

be carefull with the caulk under the braces..if you get a product that gets hard..when you block the top, you will see an up dimple everywhere you put it..especially with fresh high gloss paint...theres a specific product thats spongey, not hard...

76olds

I wonder if foam insulation in a can would work in the area's that the cushion is needed? It would be nice and easy to trim away afterwards to make it a neat appearance and paintable .

Eric

Sugar Bear

X2 ELY442 "Dont forget to lubricate the hood hinges pivot points."

Oil the hinge pivot points as part of maintenance, grease is often used where oil should be and the grease does not flow to where the lubrication is needed. Have seen hoods of that era fold from the owner forcing it closed on binding hinges...OOPS!!!

gbledsoe3

After a little research, I discovered what should probably be used between the hood support frame and the hood skin.

Lord Fusor 124 (50 ml - smaller container ~ $ 20)
Lord Fusor 300 Dispensing Gun for 50 ml ~ $45

It's a

MDchanic

That's the stuff.

- Eric

76olds

That's expensive spray foam, but I count my pennies when shopping.

coppercutlass

Just make sure that no matter what product you use its not a high solids. High solids will not flex. To better explain this imagine your car is nice and shiney and you left it nice and flat. In the sun the metal will expand but the adhesive will not so your flat hood will become wavy. like this. this is what i use at work on door skins between the skin and impact beams.

http://www.tcpglobal.com/SEM-39977_5...Q#.WB_Z5NQrI54

MDchanic

"Applications:
Sound deadening, sealing and filling of: door skins to crash bar, hood panel to supports, trunk panel to supports and gas tank filler area.

Substrates:
Primed or painted metals and all plastics.

Features & Benefits:
Matches OEM sound deadening foams
Retains its memory with no shrinkage
Expands to 10 times its size
Will not oil can
Will not absorb moisture or cause corrosion"





"DUAL-MIX Forever Warranty
Excellent sag resistance
Reduces noise and vibration
Protects against corrosion
Superior flexibility"




These look like the same product from different manufacturers.

Without specific experience, I would expect both to work well.

- Eric

coppercutlass

Some can be high solids. And will not flex with heat. So when the panel gets hit with heat the areas with the dabs will not. I was just putting that info out there. I personally like Sem products. You gotta keep in mind some will be foam and some can be more like urethane think rubbery . There is so many products that are alike but unique at the same time they all have their jobs. The fusor stuff expands the Sem stuff you can pump in and it will expand a little bit but applying it requires a little practice. Any of these products can be messy and will sag without knowing what to do. Proper application goes a long way.

gbledsoe3

Got all 4 of the stress cracks repaired. Eventually, I'll buy the small tube and dispenser of the flexible foam before the hood gets painted.

MDchanic

When I was a kid and had a base case of theses cracks, we welded shelf standards alongside the structural members - worked okay.

- Eric