would anyone have a clue what is inside the cavity behind this small hole under the tail gate? The hole is covered by a small rubber plug. 

I am working on sound deadening my car and this is a very resonant panel. Is it a good idea to spray self-expanding foam there to limit the sound and vibrations travelling? Is any water drained through it? I don't see any cables inside but would need to know that for sure. 

A panel with that many folds so close together and a highly stressed gas strut attachment point is very resonant?

 

Are you kidding?

22 minutes ago, J.R. said:

A panel with that many folds so close together and a highly stressed gas strut attachment point is very resonant?

 

Are you kidding?

haha for those who have never knocked on it from the outside, yes it is very, very resonant. Anyway do you know if there is anything inside or is it safe to spray the expanding foam in there?

 

Just thinking that maybe it's a good idea to take out the trim from there just in case the clips are in the same channel...

My Octavia 2 Estate was attacked by a bunch of motorcyclists (long story) they had seen that I had photographed the rodéo (which later on resulted in 2 serious injuries) and had blocked the road wanting to drag me out and steal or smash my phone camera, I had to drive slowly through them and they were battering the roof, windows etc.

 

The only dent was to that panel so whilst it is not thick I cant accept any audible resonance, not when you have the wobble board roof panel beside it which booms with any window partially open.

 

I totally understand closing off any hollow member that can channel road noise, the C pillar leads down to the cabin ventilators behind the bumper.

 

When I was rewiring a Galaxy I had my hand up the rear of the front wing and pulled out a squishy plastic bag from the A pillar, I thought it had been a smugglers vehicle & I had found a stash but it was the Automotive Europa assembly plant that had used a gel inside a plastic bag for preventing noise coming into the cabin via that hollow section.

1 hour ago, J.R. said:

My Octavia 2 Estate was attacked by a bunch of motorcyclists (long story) they had seen that I had photographed the rodéo (which later on resulted in 2 serious injuries) and had blocked the road wanting to drag me out and steal or smash my phone camera, I had to drive slowly through them and they were battering the roof, windows etc.

 

The only dent was to that panel so whilst it is not thick I cant accept any audible resonance, not when you have the wobble board roof panel beside it which booms with any window partially open.

 

I totally understand closing off any hollow member that can channel road noise, the C pillar leads down to the cabin ventilators behind the bumper.

 

When I was rewiring a Galaxy I had my hand up the rear of the front wing and pulled out a squishy plastic bag from the A pillar, I thought it had been a smugglers vehicle & I had found a stash but it was the Automotive Europa assembly plant that had used a gel inside a plastic bag for preventing noise coming into the cabin via that hollow section.

 

You lost me here a bit. So a) you are saying you don't think this will generate any audible noise - this I won't know until I dampen it somehow b) that the channel behind this panel is connected to the cabin ventilators behind the bumper. do you mean a rear bumper? is the channel then open from both sides? because if it;s open from one side only then I don't think it would play any role in the ventilation provided you seal it of from the close-end side

Edited 8 June, 20214 yr by lukk

Take a look with a borescope?

 

I'd be worried that expanding foam would get everywhere, come out the top, bottom and any other hole along it...

 

Maybe check if the top or bottom are open and use a spongy foam you can squeeze in and remove later?

Just pull off the C piller trim and have a look inside?

1 hour ago, langers2k said:

I'd be worried that expanding foam would get everywhere, come out the top, bottom and any other hole along it...

Absolutely right, I've seen it done with expensive consequences (boss's shoes got ruined ).

 

You can get sealed bags of expanding foam intended for making custom packaging, if you can get them the right size and shape then they would be a safer alternative.

Stick some sound insulation on the outside to change the way the panel behaves, it will make a mess but I bet it won't make any difference.

 

If it does then you know you need to work something out for the inside.

 

You have found the problem with the 1.6, it is too small for a car of this size so you have to work the engine hard to get anywhere and hence more noise.

15 minutes ago, Steviedakota said:

Just pull off the C piller trim and have a look inside?

it will most likely reveal holes for the trip clips only. I did pull it off btw when sound deadening the boot and the spaces on the sides. 

 

36 minutes ago, IJWS15 said:

Stick some sound insulation on the outside to change the way the panel behaves, it will make a mess but I bet it won't make any difference.

 

If it does then you know you need to work something out for the inside.

 

You have found the problem with the 1.6, it is too small for a car of this size so you have to work the engine hard to get anywhere and hence more noise.

 

thanks I thought about this option but temporarily sticking butyl on the outside of the car makes no sense but to check if the resonance goes away. Which we know it will.

 

As for the engine I would disagree, it pulls well enough and it's not loud at all.

 

Majority of my remaining resonance comes from the tires and the floor. Now that I have sound deaden the front doors, the B pillar and the boot I can very clearly hear this.   I have size 18 wide tires and they are just not a good idea in this car on coarse roads. I will do the floor with butyl and mass loaded vinyl, just waiting for the materials. 

 

But I guess those C pillar cavities do cause some noise at the back so why not do something about it.

Edited 9 June, 20214 yr by lukk

14 hours ago, D402 said:

Absolutely right, I've seen it done with expensive consequences (boss's shoes got ruined ).

 

You can get sealed bags of expanding foam intended for making custom packaging, if you can get them the right size and shape then they would be a safer alternative.

that's a good idea. just thinking about it perhaps I can just put a solid enough plastic bag into that think and spray the foam into it

Spray foam is very easy to control once you graduate from the aerosol type cans (which in my experience can rarely be re-used and the trigger will often stick full open covering you and the job) to a pro gun canister type.

 

With a pro gun you can control the flow from a bead like a strand of cotton to full bore and once you are used to the expansion ratio of the product you are using you can create a very smooth flush job with no excess, when the regulating needle is screwed fully home the stuff lasts for years unused & the gun will work straight away.

 

Its my bodging tool of choice now and I use several different low expansion adhesives far more than foams these days.

Get your self an inspection camera and scope it out, Screw Fix do one for about £70

On 10/06/2021 at 10:12, patrolman said:

Get your self an inspection camera and scope it out, Screw Fix do one for about £70

trying to avoid spending those 70 quid for a single one off job. trying to borrow one of someone, so far no luck

A USB camera is peanuts from AliExpress.

 

Might as well get a USB microscope at the same time!

14 hours ago, J.R. said:

A USB camera is peanuts from AliExpress.

 

Might as well get a USB microscope at the same time!

that's a very good idea, ordered one. will report what I see when I get it, which could be anywhere between 2 weeks and 3 months as this is aliexpress

Ain't that the truth, you can count on it being one or the other and never anything inbetween!