Lotus Elan

Sound-proofing the differential.

PostPost by: Quart Meg Miles » Mon Dec 31, 2012 10:00 pm

Driving an early Elan is always accompanied by the music of the differential just behind the inboard ear and this can get wearing as time goes on. Having the differential out to rebuild it presented me with the opportunity to install some sound-proofing under that thin fibreglass, which I?d been promising myself for years. When I next drove the car it felt as though I had gone deaf in my left ear as I couldn?t hear the differential and much of the exhaust noise had gone too. What a pity there?s no music on the AM radio these days.

Essentially it?s just a board of ?? chipboard, or similar bulky material, fitted in the rear V of the chassis below the glass-fibre. The first diagram shows the approximate dimensions [15" (380 mm) wide, 9?" (240 mm) deep] as I didn?t make notes or photos at the time; you had better measure your own or make a cardboard template and see if it fits closely. I included two layers of carpet felt above the board but I don?t think it was necessary, it?s the mass that counts.

Elan Diff sound proofing #1.jpg and
Basic working area.

If you have a bare chassis then you can make it permanent by bolting a larger board onto and under the chassis itself, making sure you wrap it up in waterproof plastic first, but most people will want the option of removing and refitting it after assembly without having holes drilled in the chassis. And that is a little more difficult.

There is a small gap between the top of the chassis and the body above it and there is room for 1/8? (3 mm) thick material to fit in there, but it?s worth checking your own car in case it is closed up. The idea, and implementation, was to cut a board to fit in the V and, after wrapping it carefully in thick waterproof sheeting (like the bag used for compost in the UK), bolt on top of it some 1/8? thick rigid plastic sheet, or whatever is to hand, protruding say ?? (20 mm) beyond the diagonal sides which would slot into the gap and allow the board to hang in that space. It?s plain to see that you can only fit and remove that from the top and not with the body on, so we have to cut off about 2? (50 mm) from the base of the board so that the main piece, wrapped up, can be slotted in from the back and pushed fully forward before we fit the cut-off piece separately behind it. I used another offcut of the 1/8? plastic sheet to join the two pieces of board together from underneath but any method would do, there?s not a lot of weight to support even on bumpy roads.

The second picture shows the divided board outlined in Green, the hanging plastic pieces outlined in Red and the joining plastic sheet (that I used) outlined in Blue.

Elan Diff sound proofing #2.jpg and
Placement of parts.

There may be pipes or other items in the area where the board fits so a ?dry? fitting is essential before wrapping it up; I believe the brake pipes came through one corner on my car. I had the differential and drive shafts out of the car but both A arms were still in place and it wasn?t too difficult to complete with the car body jacked up both sides fairly high, though I am not large. It might be possible to do it without dismantling anything else if there is enough height to work in, under a Two-arm hoist, for example.

26/4088 1965 S1½ Old and scruffy but in perfect working order; the car too.
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Quart Meg Miles
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PostPost by: robertverhey » Mon Dec 31, 2012 10:20 pm

Thanks Meg, nice easy mod which I'll incorporate in my resto

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