Inside Collection: Lotus Seven S4 (Type 60): Design, Restoration, and Maintenance
The rear radius arms and the associated axle locating arm for the Series 4 Lotus Seven are bespoke items. The upper radius arms are tubular and bent at the point they meet the chassis mounts. The single lower radius arm is straight and located on the right hand side, while the left hand lower radius arm is incorporated into the axle locating arm. A metalastic bushing (metal-rubber-metal) is then press fitted into the upper radius arms for attachment into the rear of the chassis, while rubber bushings are used for the axle ends of the radius arms and axle locating link, as well as the central chassis mounting. Large rubber bushings are used for attachment of the front of the lower radius arm and axle locating link to the chassis (Figure 1).
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In general the metalastic bushes in the upper radius arms corrode with time, in particular the rubber is susceptible to atmospheric degradation causing it to dry and crack, while oil and fluids cause the rubber to decay. However, the type 636 bushes are readily available and easily replaced. The metalastic bushes in the upper radius arms were dried but not appreciably affected by the fire; however, they needed replacing. These are removed by using a 10 ton hydraulic press with a 3/4” socket, while supporting the end of the wishbone (Figure 2). One of the upper radius arms with the old bushing, and after its removal, is shown in Figure 3 and Figure 4, respectively. The type bushes are readily removed from the axle ends of the upper radius arms, the lower radius arm, and the axle locating link.
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Once the bushings were removed the radius arms and axle control link were media blasted to remove all rust and residual paint. While the rear suspension components were originally painted black, better protection is obtained by powder coating. Figure 5 shows the lower radius arm and the axle locating link after powder coating by Custom Coatings (Cypress, TX). It is important not to powder coat inside the cylinder into which the new metalastic bushing is to be fitted. Any overcoat must be carefully removed.
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The new bushes, purchased from Redline Components, Ltd. (Caterham, UK), are press fitted to the upper radius arms using a hydraulic press (Figure 6), and are now ready for instillation (Figure 7). The remaining bushings are fitted during instillation in the chassis.
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This work is licensed by Andrew R. Barron under a Creative Commons Attribution License (CC-BY 3.0), and is an Open Educational Resource.
Last edited by Andrew R. Barron on Jun 18, 2012 4:23 pm -0500.
