Fixing a noisy, tinny sounding trunk lid on my Formal

[WissaMan]

I have a 77 New Yorker and when I slam the trunk lid it makes a loud tinny sound. I don't know how to describe it any better, but if you've heard it you know what I'm talking about. It really sounds bad, not the kind of sound a luxurious car should make I looked at a 73 Imperial a while back and it did the same thing. It seems to be the outer skin is hitting the inner reinforcement because if I put my hand on the middle of the lid as I close it, the sound is damped.

Do anyone else have experience addressing this issue?

I am pondering shooting some expanding foam inside it to eliminate the noise. But I'm worried as the foam expands it may make the outer skin bulge, which would be really really bad! Does expanding foam exert a lot of force as it expands? Another idea would be to get a can of rubberized undercoating with the long hose and spray some of that inside.

 

[CBODY67]

Use some thicker, spray-on undercoat. All you need is to dampen the sound, not put additional humps in the sheet metal.

SLAM? Adjust that rear sticker and lock so you can latch it with finger pressure. Won't hasten the disintegration of any rear speakers that way. EASY to adjust!

Enjoy!
CBODY67

 

[polara71]

Don't slam it. Nature of the beast I suppose. All I've had sounded like that but it is part of the cars character. I wouldn't spray anything on it but if is really bothering you, its your car.

 

[CBODY67]

I suspect there might have supposed to have been some dabs of thick adhesive between the skin and inner structure, as on a hood? Just that this one missed that application?

 

[Justin Plant]

You used to be able to buy strips of black adhesive "dum dum" at Lowe's. A friend of mine got a box of it for a Samurai we were working on years ago. I'd go with something like that before spray foam.

 

[WissaMan]

I saw a video of a guy that owns and compared an early 70's Imperial, Lincoln, and Caddy. His Imperial trunk lid did the same thing.

There's no access for any kind of adhesive strips with the trunk lid, but that'd be an idea for our 68 front hood where the adhesive bonding stuff let go. I'm talking about spraying stuff inside the trunk lid btw, in the cavity between the inner and outer skin, not on the surface where it'd be visible.

I'll go the undercoating route and look for a can that comes with the hose and spray nozzle. I probably won't get to this for a while but when I do I'll let you know the results...

 

[73Coupe]

@vdk2010 has been through this, I recall, and had some bulging of the outer skin.

I recently saw this product (below) at the lumberyard, and wonder if it would be a good application for this?

 

[WissaMan]

That sounds like that'd be the most appropriate in terms of expanding foam. I'm not sure I'd want to risk it though. If it causes bowing, I don't see how you'd ever fix it, except maybe to apply heat and weight on it.

But if one was going to use expanding foam, I would recommend putting a flat panel with a weight on it on top of the trunk lid after spraying. That would hopefully keep enough pressure against it to prevent the foam from causing a bulge. But on the other hand, if the weight causes the sheet metal to bow inward, the foam could quite possibly fix it into that position too.

 

[CBODY67]

"Bowing" would happen in the area of least resistance. Which would be the outer skin as the inner structure is stamped into a particular shape. Maybe just some quick spritzes of the spray foam? NOT to fil it up, just make some connection between the inner and outer metal, for light support.

3M used to have a "hood flutter" item which "glued" the hood ohter skin back to the inner structure. Not expansive. Maybe something like that?

Or maybe just finesse the adjustment of the latch and striker so a "slam" is not needed?

CBODY67

 

[Big_John]

That sounds like that'd be the most appropriate in terms of expanding foam. I'm not sure I'd want to risk it though. If it causes bowing, I don't see how you'd ever fix it, except maybe to apply heat and weight on it.

But if one was going to use expanding foam, I would recommend putting a flat panel with a weight on it on top of the trunk lid after spraying. That would hopefully keep enough pressure against it to prevent the foam from causing a bulge. But on the other hand, if the weight causes the sheet metal to bow inward, the foam could quite possibly fix it into that position too.

There's a product called "Lizard Skin" that is a spray on. There's also a home made version that's a ton cheaper. https://www.hotrodders.com/threads/alternative-to-lizard-skin.103610/

I did the home made version. Mixed the micro balloons with latex paint. I took the deck lid off and plugged all the holes but one, then poured the mixture in. Sealed the fill hole and just tipped and turned the deck lid to cover the inside. It helped some, but I think I should have done a couple more coats. I was pressed for time as the car was headed to the body shop in a few days.

I think I have almost a whole box of the micro balloons left if you want to try it. More than enough to do several deck lids. If you want it, reimburse the postage and it's yours.

 

[WissaMan]

That's fascinating, I love learning about new DIY things!

 

[CBODY67]

(Do the micro-ballons expand and contract like normal balloons do with temperature changes?)

 

[mopar preferred]

Do not use foam!
A member @vdk2010 did that on his Imperial trunk lid and ruined it.
I don't remember how he fixed it, but his car is going to be perfect, so I know he found a way.

 

[SIPLOWGUY]

Never thought much about this. Many good ideas here to ponder.

 

[vdk2010]

After talking to the manufacturer, who assured me it was the right product for the job, I used Petec (a German brand) 2K body foam. Guess what? It wasn't. Now, my trunk lid is a wavy mess.
I can tell you, once it's messed up, it's not fixable. Nothing I tried solved the problem. For now, I have to live with it, especially since my trunk lid is freshly painted.

My only option is to acid dip my trunk lid again someday and start from scratch. I'd split the two panels, acid dip and e-coat them individually, apply glue, and then weld them back together. But that's obviously not an option for you with an original hood.

In my opinion, the trunk lid will always be a huge, flimsy sheet of metal that is prone to bulging. I would never use foam again because it's too strong and will always distort the sheet metal.
Back then, the factory put adhesive between the inner and outer panels before welding them together. However, since there are no holes in the inner panel other than in the hood for reapplication, the only option would be to spray something between the panels.


A while ago, though, I saw a video from AMD talking about SEM Dual-Mix Flexible Urethane Foam. Kevin Tetz used it to do exactly that on a roof.
Dual-Mix™ Flexible Urethane Foam | 39357 | SEM Products

I'm a burned child, so I would never try foam again regardless of what a manufacturer claims about their product. But maybe you will have more success than I did!

Here is what I did:

I drilled two holes into the bottom of the Trunk Lid and sprayed foam through them and the hinge holes into both the X'es.

You can see the foam lifted the outer skin about 2-3mm in sections.

You can see it in the reflection...

 

[Big_John]

(Do the micro-ballons expand and contract like normal balloons do with temperature changes?)

They probably do, but it's going to be insignificant because of the size. The micro balloons sold for this use are about 60 microns (.0023") in diameter. They are so light, you have to pour them where the air is very still and you should wear a mask so you don't inhale any.

 

[73Coupe]

After talking to the manufacturer, who assured me it was the right product for the job, I used Petec (a German brand) 2K body foam. Guess what? It wasn't. Now, my trunk lid is a wavy mess.
I can tell you, once it's messed up, it's not fixable. Nothing I tried solved the problem. For now, I have to live with it, especially since my trunk lid is freshly painted.

My only option is to acid dip my trunk lid again someday and start from scratch. I'd split the two panels, acid dip and e-coat them individually, apply glue, and then weld them back together. But that's obviously not an option for you with an original hood.

In my opinion, the trunk lid will always be a huge, flimsy sheet of metal that is prone to bulging. I would never use foam again because it's too strong and will always distort the sheet metal.
Back then, the factory put adhesive between the inner and outer panels before welding them together. However, since there are no holes in the inner panel other than in the hood for reapplication, the only option would be to spray something between the panels.


A while ago, though, I saw a video from AMD talking about SEM Dual-Mix Flexible Urethane Foam. Kevin Tetz used it to do exactly that on a roof.
Dual-Mix™ Flexible Urethane Foam | 39357 | SEM Products

I'm a burned child, so I would never try foam again regardless of what a manufacturer claims about their product. But maybe you will have more success than I did!

Here is what I did:

I drilled two holes into the bottom of the Trunk Lid and sprayed foam through them and the hinge holes into both the X'es.
View attachment 743023

You can see the foam lifted the outer skin about 2-3mm in sections.
View attachment 743022

You can see it in the reflection...
View attachment 743024

You could probably just grind the paint off of the top, skim coat the entire lid with filler, and repaint it, and it wouldn't be noticeable. With only 2-3 mm I wouldn't think that you would have to remove the foam. But, as you've said, it's already painted, so is it really worth it to you - and then there's the color match problem if you don't have any of that paint left over.

 

[vdk2010]

You could probably just grind the paint off of the top, skim coat the entire lid with filler, and repaint it, and it wouldn't be noticeable. With only 2-3 mm I wouldn't think that you would have to remove the foam. But, as you've said, it's already painted, so is it really worth it to you - and then there's the color match problem if you don't have any of that paint left over.

My painter did his best to fix it, but it's still wavy. I paid a lot of money to have my body man straighten all the panels so that I wouldn't need to apply thick layers of filler. That makes the trunk lid sort of a "shame" for the rest of the car.
For now, I'm focusing my time and money on more important things to get her on the road. However, as I said, I will redo the trunk lid from scratch someday!

 

[WissaMan]

Thanks for sharing your experience and I'm sorry it worked out that way. That's exactly what I was concerned about. But try to look on the bright side....your trunk lid is perfectly quiet now :\

When I go to do mine, my plan will just be to use some sprayable rubberized undercoating. The kind that comes with a tube and a 360 degree nozzle at the end. Then just spray a few coatings into the "x" cavity. I should be able to do that w/o removing it from the car, which is also a plus. Probably won't make it dead quiet, but should dampen it somewhat.

Interestingly, the trunk lid on the 68 Chryslers don't make this noise. Maybe there's more of a gap between the inner and outer skins so they don't touch each other when vibrating.

 

[73Coupe]

My former '73 had a tinny / separated trunk skin, and there were remnants of a hardened orange colored substance that would fall out occasionally, what the factory used to glue the halves together.