Rubber bushing

A rubber bushing is a device, primarily used in suspension systems, which separates the faces of two metal objects whilst still allowing a set degree of movement. This movement allows the suspension parts to move freely for example when traveling over a large bump but minimizes transmission of noise and small vibrations through to the chassis of the vehicle. A rubber bushing may also be described as a flexible mounting or anti-vibration mounting.

Uses

Uses for the rubber suspension bushing include anti-roll bar links and mountings, shock absorber mountings and front wishbone assemblies to name only a few.

Certain high speed in-line internal combustion engines are prone to torsional vibration of their crankshafts; the straight six and straight eight engines being particularly prone to this problem due to their long crankshaft length. Although straight eight engines faded from the marketplace in the 1950s, many straight six engines have and still do feature crankshaft vibration damping utilising rubber bushes. The 3,442 cc Jaguar XK 6-cylinder engine of 1948 and most subsequent versions of the ubiquitous Jaguar XK engine used a proprietary Metalastik vibration damper to protect their crankshafts from potentially damaging torsional vibrations. To quote William Heynes in ref.<ref>Heynes, W M. The Jaguar Engine, a paper presented to the Institution of Mechanical Engineers on 27 February 1953</ref>, "The Metalastik damper consists of a steel plate to which is bonded, through a thick rubber disk, a malleable iron floating weight. Variations of the weight, rubber volume and mix, give these dampers a very wide field over which they can operate."

Advantages

Advantages of using a rubber bushing over a solid bearing system are that less noise and vibration are transmitted through rubber. Rubber also requires little or no lubrication.

Disadvantages

Disadvantages of rubber bushings are that they can deteriorate quickly in the presence of mineral oil and that extreme heat and cold can also lead to failure.

The flexibility of rubber also introduces an element of play in the suspension system. This may result in camber, caster or toe changes in the wheels of the vehicle during high load conditions (cornering and braking), adversely affecting the vehicle's handling. For this reason a popular aftermarket performance upgrade is the replacement of rubber suspension bushes with bushes made of more rigid materials, such as polyurethane. Polyurethane bushes are also available for many vehicles with the same characteristics as the manufacturers original bushes - but with greatly increased durability. This is useful on vehicles that have a reputation for wearing out standard rubber bushes, but harder bushing with increased harshness is not wanted.

Trademarks

Trademarks for particular types of rubber bushing include Isolastic, Metalastic and Metalastik.