Gearbox Tunnel insulation - that old chestnut!

[trigolf]

Evening all,

Sorry to bring this up again, but I've been following the various threads about this for some time and want to fit the best cost effective solution. I've got a Vit convertible, so I'm not so bothered about keeping heat out. I'm more interested in transmission/engine noise insulation.

The original hardboard cover was in very poor condition, I tried to repair it with fibreglass matting/resin years ago,but it wasn't very successful, so I bought a fibreglass tunnel cover. It needed a lot of work to get it fitting ok. Thr original bagged insulation was knackered and not fit to re-use. So I got some white foam wadding from an upholsterer's, which I thought was a suitable substitute, and put this into bags and stuck to the inside of the tunnel. I also glued a bubble section  rubber seal around the edges.

Over time, I've come to the conclusion that the foam wadding is not the right thing for the job and the fibreglass cover transmits more noise thorough it than the hardboard one did.

So to achieve airborne noise insulation do I use something like 2mm SilentCoat on the inside of the tunnel and even the outside? Or do I find some closed cell foam sheet about 25mm thick and stick that to the inside of the tunnel?

Opinions please !

Gav

[johny]

The problem on the inside is the heat, oil and road dirt so I dont think foam is ideal and silent coat etc would be preferable. Saying that I didnt use anything but did fill the underside of the tray area with expanding foam (this area obviously cant be insulated on the top) then stuck a thin foam backed carpet I had left over from my bathroom over the complete topside before finishing off with the usual molded carpet. It works well and the main noise source in my fixed head Vitesse is from poor aero dynamics😁 

[Iain T]

1 hour ago, Mathew said:

12mm foam, self sticking.

Mathew, good idea. I've used the same ali sheet on the inside but using foam on the outside could help with noise. My carpet is pretty detachable and loose so it should fit. 

Iain 

[Colin Lindsay]

Dodomat or the like stuck to the underside of the bulkhead panels, or up behind the dashboard and in the footwells, will kill a lot of the engine noise too.

[Badwolf]

I am very slowly repairing my cover but COVID has struck!! I eventually intend to apply SilentCoat or DoDomat to the underside after I have sorted the access panels for gear oil, clutch slave and Speedo cable.

[Stratton Jimmer]

16 hours ago, Iain T said:

Mathew, good idea. I've used the same ali sheet on the inside

Me too. The aluminium type bubble insulation, attached with spray on contact adhesive. You can overlap it and use multiple layers in key areas. It is weather proof, sound deadening and provides excellent thermal insulation too.

[trigolf]

Ok. The ballot is now closed. I'll go for Silent Coat inside and out. Thanks all!

Gav

[Peter Truman]

I’ve just completed the Vitesse’s Fibre glass gearbox cover with Dynomat on the inner and a 1/2in fibre carpet bitumen covered underlay on the outside. Dynomat is a thick bituminous  sheet with a thick aluminium flexible outer which is easily moulded to the shape required and sticks like hell never to be removed.

The fibre underlay was a kit I brought for a Herald locally here in Aus off eBay a full kit good quality and fitted well. Where the kit was made I have no idea but each section was individually sealed in a plastic bag with sticker saying where it went the bituminous cover stops it fraying too much.