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Old 11th April 2020, 08:51
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One challenge when using a Spitfire as a donor is locating the rear suspension radius arms, and that's what I've been focusing on over the last few days.

The Herald/Vitesse chassis has a full perimeter frame consisting of front, centre and rear outriggers connected by side rails, and the radius arm brackets are bolted through the rear outriggers, giving them a solid location.

On the Spitfire, the chassis has stubby outriggers front and centre, but nothing at the back, and the radius arm brackets are bolted directly to the bodyshell just above floor level.

I've seen some imaginative approaches to locating these vital suspension components on various kitcars, including at least one that used modified radius arms that extended all the way to the centre outrigger stubs, making them about three feet long.

I wanted something a bit more factory spec, so decided to pretty much copy the Herald/Vitesse setup -







The sharp-eyed may have noticed that I haven't used rear radius brackets, but front wishbone brackets, and the reason for this is twofold:

The brackets that came in a box of parts with my donor turned out to be for a Rotoflex car, so are completely the wrong angle as they are mounted about six inches inboard of non-rotoflex brackets.

If I did have the correct brackets, the mounting studs are too short to go through the 50mm box-section that I'm using for my perimeter frame, so I'd have had to drill them out and replace them with longer studs anyway.

As I had a selection of front wishbone brackets 'on the shelf' and they have studs that are long enough (and are far more substantially built than the rear radius arm brackets) I decided to give them a go.

To get the necessary angle I fabricated some angled plinths (out of an old sofa frame I'd kept), and you can see these best in the first picture above, which is partially completed. The wishbone brackets are very slightly narrower than the radius arm brackets, so to get the bushes to fit I had to grind about 2mm off the metal tube inside the bushes.

In the other pictures you can see that I've welded steel plate across the top and bottom to seal the unit and add extra strength, and what you can't see is that the stud and extra bolt both run through 2mm wall tube welded between the plinths to prevent the box-section from being crushed when the nuts are tightened up.

All in all it's turning out to be a robust and quite elegant solution to the problem.

More later.
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