Spray Foaming Crossmembers

[FoMoCoBronCo]

Can someone provide some advice around adding spray foam to inside the body crossmembers? I’m working on a variety of sound deadening / heat reduction methods and I haven’t seen anyone discuss this. There are holes that would allow for a nozzle to be inserted, plus I could drill some additional small ones for better / more even coverage.

My initial concern was that it could hold water up against the sheet metal and cause rust, but I also seem to remember that certain types of spray foam (open or closed cell?) are waterproof and don’t let water in?

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[73azbronco]

my e450 frame has foam sprayed all over the place, it's an RV, no rust. I would not put it inside a frame though. What is that shiney dimpled metal?

 

[FoMoCoBronCo]

my e450 frame has foam sprayed all over the place, it's an RV, no rust. I would not put it inside a frame though. What is that shiney dimpled metal?

That is DEI heat shield I have applied to the underside of the body for heat control / sound dampening.

Technically I would be applying it inside the body crossmembers, not the frame. Would that make a difference in your opinion? Or still problematic?


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[ba123]

I'd think it would be fine as long as you were 150% sure no water could get in. If it does, it will rust for sure and it will keep the moisture there. That's why there are all the holes in the those crossmembers...to let the water OUT.

 

[jmhend]

I would not use spray foam. Have you considered an internal frame coating like this: Internal Frame coating

 

[73azbronco]

On all the builds, some 6 figure, I cannot recall ever seeing the inside of a crossmember foamed. I would not. If it was a thing, why not foam inside of frame itself? I don't think you would be reducing any measurable noise or heat.

My sound heat deading is sprayed in truck bed liner, about 1/8th thick, then dynashield or matt and then material you used over the hump and up the firewall inside cab. Over that is the really pricey high quality carpet which was about $2,500. I have about 3/4 thickness of all the insulation, no heat, no sound through floor.

 

[bmc69]

I experimented with using expanding foam in the square tubing of a boat trailer. It was a disaster....I never saw tubing rot out so bad and so quickly.

 

[Broncobowsher]

Had a BroncoII that got rust in the A-pillars. where it was foamed at.

The OEMs can get away with it now. They have decades of knowledge in getting it wrong.
As for doing it DIY, I'm going to say what I am seeing is going to cause issues down the road. The OEMs doing it are doing specific areas for specific reasons. The crossmembers you are proposing, I don't see any gains by foaming those. And I have a little experience working with the OEMs and why things are done in different ways.

 

[ep67bro]

I wouldnt do it. I had a 1970 Bronco that someone used Spray foam to fill the lower door post and parts of the rockers. Not sure what came first the rust or the repair but the foam was about the only thing holding the bronco together when I got it. The body cross member is such a small area I cant see much gain by doing this and the chances of catching water and causing major rust far out weight any gains.

 

[Wild horse 75]

Don’t do it. The foam will hold water against the sheet metal and rot it out quick. Get lizard skin spray dedener and spray it in there nice and thick. That’ll keep them from becoming an echo chamber.