Soundproofing

Built-in Quietness

British Leyland marketing emphasised the "comfort" and "built-in quietness" of the GT, as a true grand tourer. So considerable thought must have gone into the car's sound insulation to achieve a balance between sportiness and refinement (and cost). 

But information on the soundproofing applied by the factory is elusive. Much of it seems to have been attached to carpets or trim panels, and not reproduced well or at all on modern after-market replacements. 

That makes investigating the details quite an interesting exercise...

"Built-in quietness" as standard - from the 1972 GT brochure (click to enlarge)

1) Starting at the front of the car, there were of course two large rubberised felt pads glued to the underside of the bonnet. The B Series engine is notoriously tappety, and they no doubt contain some of that top-end chatter. Clausager notes that rubberised felt replaced "fibroleta and felt" from June 1972 for better sound insulation.

Original under-bonnet pads on a 1975 LE car (dealer's picture).

The bonnet seal may also reduce engine noise a little, and there are four rubber buffers whose role is to stop the bonnet rattling. Two at the side and two on the grille.

2) In the cabin, the footwell floors and kick panels were lined with large sheets of an adhesive bituminous material, incorporating cut-outs for the mat-fixing poppers.

Footwells from a 1973 car, showing the large sheets of stippled 

insulation, painted body colour, on the floors and kick panels (photos from Ebay).

As can be seen from the small scraps remaining, a white foam or fleece material may then have been glued on top of the pads. (But I've only seen it on this car so it could be a later addition.) Each of the four footwell mats themselves had a backing layer of rubberised-hessian insulation:

Reverse of footwell mat from a 1974 GT.

3) At either end of the cabin floor, a layer of fleece-based insulation was glued to the back of the toe-board trim panels and the heel-board carpet. The material is like loft insulation in texture and appearance, so probably provided heat insulation too. It was covered by a thin plastic film.

Fleece insulation. Top photo from MG Experience forum, bottom from a '74 car (damaged).

4) Pads, made of the same material as used on the floors, were located inside the doors and the C pillars to damp-out panel drumming:

Door pad on my 1973 car.

5) At the rear of the car, each also C pillar contained a large foam wedge, the purpose of which is not immediately obvious.

C pillar foam from my 1973 car.

6) The quality and thickness of the original carpets is noticeably better than some after-market kits. (Clausager notes improved, thicker carpets were adopted from August '72.) In addition to a good depth of pile, the battery-cover piece, plus the tunnel piece, also came with integral felt underlay. As mentioned above, the heel-board piece was backed with fleece insulation. (The load board piece and the boot pocket liners do not seem to have had any backing.)

Battery cover carpet from a '74 car.

The underlay came as a separate moulded piece in the case of the rear wheel arches.

Rear wheel arch underlay being expertly fitted.

7) At the back of the car, the boot loadboard had a large rubberised felt pad glued to the underside, similar to those used under the bonnet.

8) Finally, a black wrinkly tar-like substance was sprayed around the front bulkhead, from the cabin side, in a slightly hit-and-miss manner judging from the application on my car. Presumably this has a sound-deadening role.

Wrinkly spray stuff on my 1973 car.

Please, er, shout if you think I've missed anything!

        

               'Cum on Feel the Noize' was another No. 1 Hit for Slade in Feb. 1973 - but British Leyland weren't so keen.