Hood Deflection at Speed

[izzyandsue]

Mudders,
i noticed today (being new driver here) going past 55 mph the hood deflects quite a bit. I realize is a long hood, but i was doing 75 eventually, easy driving with a hard cross wind that was making other cars struggle. The hood deflects a lot, is that normal? reminded me of last time I paced a corvette on a track and those long hoods flex and flex.

The side mirror was doing the hula dance, but I know that is normal and can be fixed with zip ties.

 

[cpcc]

hood shouldnt deflect at all.

 

[LFD2037]

The adhesive that holds the hood to the 'braces' has deteriorated.
Remove hood
lay upside down on blanket/in grass/something soft
remove heat 'blanket'
apply adhesive to hood or braces
set weight on braces so they're tight to hood
let dry
re-install

 

[cpcc]

Great thought. Additionally, would it be worth while to check the play in the front latch and rear hinges?

 

[retrofive]

 

[Tapage]

this is interesting .. I make a hole in my hood for my top mounted IC and I didn't detect ( with my eye sensors ) any deflection at any speed .. sure I rarely broke the 60 ish mph barrier ..

 

[Mr Cimarron]

The adhesive that holds the hood to the 'braces' has deteriorated.
Remove hood
lay upside down on blanket/in grass/something soft
remove heat 'blanket'
apply adhesive to hood or braces
set weight on braces so they're tight to hood
let dry
re-install

I was noticing this the other day. What kind of adhesive should be used?

 

[hamishpotter]

I feel like an idiot but what is 'hood deflection' / what is the hood deflecting ?

 

[izzyandsue]

It means the "skin" of the hood, closer to the windshield, wobbles, or looks like waves being pushed around by water. Very common on fiberglass cars at high speeds where the force of the wind can "deflect" the hood surface. I may have an aftermarket hood, will dig into to that

 

[LEGHORN]

Could a seam sealer be used as the adhesive?

 

[LFD2037]

I haven't done mine yet but I'll be using either a 2 part epoxy or a Liquid Nail type product. There's no reason you'd ever want these 2 pieces to ever come apart so use something strong that a) won't eat metal/paint & b) can handle heat.

 

[cruiserdan]

Select the adhesive carefully. Too hard and the panel gets deformed. Too soft and it does not solve the problem. Incorrect properties are easily out there. Consult a bodyman with all his s*** in one sock for a recommendation.

 

[Golgo13]

The adhesive is similar to expanding foam like you buy at the hardware store. The idea is that it should be a little flexible, but not too flexible and stiff but not too stiff. basically, do what CruiserDan said.

The same stuff is used for braces in the doors and the roof on most cars these days. It should be available from an eastwood type company

I would also consider checking the adjustment of the latch and hood-bumpers.

 

[greentruck]

Another commonly available product is the foam-in-a-can made specifically for insulating around doors and windows. It has a very limited expansion designed to fill but not expand. Do NOT use the regular foam-in-a-can as it will over expannd and lead to lumpy hood syndrome.

I did mine with the hood on the truck, raised. I took the back part of the insulation loose by removing the clips . This allowed it to hang free so I could work behind it. Used just enough, don't pump it full, into the space between the bracing and the hood. Reattached insulating pad.

Be sure to lay newspapers or something else to protect from any drips into the engine compartment. The hood clips holding the pad are more likely to break than not. Napa supposedly carries the big-header clip needed. Auto Zone didn't so I used anothe clip along with fender washers to refasten.

Pay attention to CDan's warnings, even if you take my shortcut. The hood will get unsightly fast if you flop it on the ground, ding it from the inside or use too much or expanding foam. You can go back and add more foam later, so if in doubt, don't over do things.

 

[Hornd]

Did mine last night.

• Be aware removing the clips will likely cause them to break

• The Ribs were completely separated from the skin.

• You will need a step stool to reach the ribs at base of hood.

• If you do remove hood take a Sharpie and trace around brackets before removing to ensure consistent alignment
• Wear gloves as that foam is very unforgiving

**Don't ask about the wires to the LED lights that's another post.

The foam was ~$5 at Home Depot, took 1 can

 

[2fpower]

I have had 3 80's that had this issue. I tried fire rated caulking; however, it got too hard and brittle. I used seam sealer (not self leveling) last time, seemed to work great.

I had not seen people use foam for this before. Not sure if that is my first choice. MSDS sheet on the Loctite says long term exposure to 194 degrees max. Given a 200 degree engine is inches away from it, not sure it will stand up over time. Also, not sure if it has fire retardant properties or not.

There is fire block foam that is similar to the product you used, and has fire rating.

 

[scottryana]

I would use an actual bonding product. But you would have to remove the hood. The foam just fills the space between the skin and rib, it doesn't actually bond them together. The only problem with the good bonding products is that they have proprietary application guns. Some of the application guns are close to $200. My hood no longer has this problem after the body shop, but After removing the headliner I noticed the ribs of the roof do. So I am going to go back to the shop and see if they will "rent/loan" me the gun if I buy the product and just apply it in the parking lot and rig up some way to brace the ribs while it sets.

 

[plutonius]

I'm in the same boat and need to get on this as well. What's everyone's thought on re-installing the heat blanket? Mine looks like a dirty diaper...

 

[2fpower]

You can typically purchase a seam sealer gun on ebay for a reasonable amount.

My gun roams between members here in KC.

 

[scottryana]

You need something if you care about your paint. I am in the middle of my own heat reduction method, but the difference between where the heat deflection is and isn't is startling just with bare hand on the outside of the hood.