The 'E' Type Forum

As my car has a 5-speed conversion and a custom-made gearbox cover, there's rather a lack of sound deadening between the gearbox and the interior - just the metal cover and the console and a thin layer of Koolmat.

One small winter project is to increase sound deadening in this area. Some of you may say "its an OTS, why bother" and you may be right but I'd like to see if I can suppress whining in intermediate gears. The whining is not excessive and (according to CMC at least) is "normal" for this box, but I do notice it.

Anyway, I have been experimenting with flexible polyurethane foam - the sort where you mix the two liquids (polyol and isocyanate), pour them into a mould, and watch the foam expand and then set. I used thin plastic bags to sit in the gaps between box and upper tunnel areas (underneath the gearbox cover) and so far so good - it makes nice chunky pieces of PU foam which are moulded to the shape of the gearbox casing and sit happily in place but are flexible enough to be removed from the top to access filler plugs, speedo drive etc. I'm using a mix designed to give a medium-density foam.

I'll probably cast some more foam to fit between gearbox cover/tunnel and the underside of the console, and then see how much (if any) reduction in noise transmission I can notice in the spring, then report back!

Has anyone else done anything similar?

I'll be interested to hear (!) how you get on. Is yours a Getrag by any chance?

Ultimately, sound transmission through air is deadened by mass between source and detector (your lug 'oles) and I'd expect a denser foam to mask more noise, but we need flexibility of course. Maybe you can mix some foam up with sand in the mix? It's inert at least.

I've thought of getting a thick sheet of lead and folding it over the gear case and/or over the transmission tunnel cover and maybe even sticking some to the underside of the console top. Sides of the tunnel too come to that. The shebang probably will still weigh less than the old cast-iron box.

The problem nowadays will be finding some honest lead...!

Peter,
It's not as inert as you'd like to think. If it starts burning, the smoke is ACRID and extremely toxic. I mistakenly put some intro a microwave a few years back and I almost didn't make it to the kitchen door - the effect is that immediate.

If you want a denser foam, do it (partially) under vacuum. That way the co2 will be evacuated and there will be less "holes" in the structure.

FWIW, a large proportion of our repro plastic parts are made from PU resin now, as are many custom interiors for high end low productiuon run sportscars (Porsche being one example).

kind regards
Marek

Pete,
Its a JT5, not a Getrag. Aluminium case, and ATF rather than good old EP90, so I think you get a bit more of the gearset noise escaping the box than in an original unit. I went for as dense a foam as I dared for it still to be flexible enough to squeeze in and out of position.

I will report back but probably not till the spring as I have a laundry list of other minor jobs to do over the winter.

Righto. That's a downside of all alloy boxes - what noise there is does tend to escape more than with a cast-iron casing and as you say oil viscosity has an effect. You don't have much room at the sides with a T5 so i defintely cannot see any normal foam attenuating much noise across what, a 1/2" gap? I think a sheet of lead or double bitument type panels would be better than foam.

Bear in mind it is always better to prevent heat or noise getting into body panels than trying to prevent them emerging once absorbed. Sound insulating within the tunnel is your first stage I think, as you appear to be doing.

Marek - I was referring to the sand as an inert foam filler, not the foam itself. If your microwave manages to melt silica, I bet your pasties are piping hot :-)

That's right, Pete - I'm casting foam pieces to sit between the upper sides of the T5 and the tunnel and tunnel cover. As you say there's not a lot of air gap so there's only so much I can do. Then I'll turn to filling some of the space between the tunnel/cover and the central console.

John

Gents,

This discussion re foam and lead to absorb sound put me in mind of a product I bought a number of years ago to line the floor of a Series 1 Land Rover. It was called "CoustiLam". A quick search in Google turned up this: http://www.acoustic.co.uk/H&H/Enabs.htm Details can be found at the foot of their web page.

Regards,
Jim