Under hood insulation/noise material

So about 10 years ago hail damage caused me to have the top of the XJ repaired, and they talked me into replacing the hood as being cheaper than fixing the dents, probably not wrong. But ever since I had noticed the hood vibrating in the wind and had wrongly assumed that it was due to a thinner aftermarket hood material.

Now I'm remembering that before there was a sort of recycled fiber insulation under the OEM hood that the new one didn't had, which fully explains why the hood feels flimsier in the wind.

Does anyone know what that material was so I could replace it? I know Dorman sells an under hood replacement that reviews as thin and not really what was there originally. I'd rather find a thicker, denser, and most importantly heat resistant material and cut/fit it to the holes in the hood with retention clips than use a cheap knockoff. Anyone tried to do this?

I dont see how some fiberglass insulation makes the hood feel less flimsy. I ripped mine out a while ago. Hood still feels like standard over built jeep hardware.

Simple matter of mass, it dampened the vibrations simply by being heavier. To be more clear, prior to the hood replacement, I couldn't see any amount of movement in the hood. Afterward it would shimmy at certain speeds.

If a shimmy, wouldn't want something like Dynamat to dampen the vibes ? I doubt 18 oz of free hanging fiberglass will do much.

Yeah, the fiberglass attaches to the substructure anyway. If the aftermarket hood is indeed so much thinner that the sheet steel vibrates in the wind you may be best off getting a jeep hood. If it's the whole hood vibrating most likely your stops just need adjusted up.

It's just the center of the hood vibrating, so I suspect thinner aftermarket version after all.

the padding gives zero structural support. it exists either or both for sound and heat insulation. It appears latter model jeeps lacked this padding, perhaps do to the need to remove heat given the catalysts added in the engine bay. My buddies late model xj lacks the padding, his hood gets very hot. I suspect the padding trapped heat more, but did keep the outer surface from getting so hot, which may help paint life?

Get micrometer on your hood to determine how thick the metal is, it might be an issue of thin metal used on an aftermarket hood?
I restore old cars, and will pay a premium for original fenders and hood even if in need of repair, verses most of the reproduction body panels, that are oft thinner or lack the correct shape.

You can squirt some automotive mastic between the underhood cross braces and the sheet metal. Sounds like this may be your issue.

Construction adhesive may work too

8Mud said:

You can squirt some automotive mastic between the underhood cross braces and the sheet metal. Sounds like this may be your issue.

Click to expand...

As in inside the braces? Just to get it to stick to them better? I'd assumed they were spot welded but haven't really looked closely. Also, not familiar with mastics (apart from the term). Do you have a product in mind?

I agree with securing the bracing to the hood. Some auto manufacturers
use a panel adhesive for this.

There's a product called DEI BoomMat that is designed to dampen
noise and it also adds some structural rigidity to panels. It comes
in a spray can and is very easy to apply.

Automotive seam sealer will do the job and be cheaper than Dynamat.

asymptonic said:

As in inside the braces? Just to get it to stick to them better? I'd assumed they were spot welded but haven't really looked closely. Also, not familiar with mastics (apart from the term). Do you have a product in mind?

Click to expand...

Mastic is a generic term body panel adhesive or body panel sealer are likely replacements. I tend to use Loc Tite (Henkel) products when available, 3M is also good, Liquid Moly also makes some acceptable stuff. I like Henkel products because there is no hype, they perform as advertised.