The standard rubber bushings used at the suspension pivot points of every classic MG were specified by BMC and BL with a particular balance in mind, enough compliance to absorb road inputs and small-amplitude vibrations, with enough stiffness to control suspension geometry under cornering loads. Over decades of service the original rubber bushings harden, distort, and eventually crack, losing both their compliance and their geometry control, which manifests as vague steering, inconsistent cornering behaviour, and accelerated tyre wear. Polyurethane bushings replace the original rubber with a synthetic compound that is more durable, slightly stiffer, and substantially longer-lived, and fitting them is one of the most cost-effective handling improvements available, one that owners notice immediately on the road.
Full Suspension Bush Kits
Polyurethane bush kits are stocked as complete sets covering every bushing on the car, front-suspension wishbone inner and outer bushings, anti-roll-bar mounting and drop-link bushings, rear-spring eye and shackle bushings, spring pads, and the various smaller suspension and steering bushings, packaged by model with the bushings appropriate to that model's specification. For owners working through a suspension overhaul, fitting the entire kit at once is the cost-effective approach, as the labour involved in dismantling the suspension is the same whether one bush or twenty are renewed, and renewing all of them at once means the work does not need to be repeated for the foreseeable future. The bushes are manufactured using hot injection moulding for improved dimensional consistency between bushes within a batch, and where the geometry allows they incorporate an internal cross-hatched bore design that retains lubricant within the bush during service, eliminating the squeak that polyurethane can otherwise develop and reducing the stiction that causes a bush to grip and release rather than rotate smoothly. The kits are typically guaranteed for two years against defects.
Compound Choice & Driving Characteristics
Two compounds are typically available, a fast-road specification that is slightly stiffer than standard rubber to minimise deflection and sharpen response but sufficiently pliable to avoid a harsh ride, suited to everyday use with a meaningful improvement in handling, and a race specification that is firmer again for committed fast-road and competition use where maximum precision takes priority over ride comfort. The effect of polyurethane on the driving characteristic is positive but noticeable, the steering more direct, the suspension more communicative, the cornering attitude flatter and more controllable, tyre wear more even because the contact patch stays more consistently located, and cabin noise typically reduced because the firmer bushings do not develop the squeaks and rattles that aged rubber produces. The trade-off is that small-amplitude road inputs are transmitted to the body slightly more directly, producing a marginally firmer ride that some owners welcome and some find too direct, a personal preference, with polyurethane particularly favoured by owners running cars on a fast-road or competition specification. Heavier-duty bush options exist for some applications, the V8 inner wishbone bush, for example, being fittable to the four-cylinder MGB for improved durability.
Installation & Service
Polyurethane bushings install in the same locations as the original rubber bushings, typically pressed or driven into clean housings free of burrs, rust, and old paint, as damaged internal surfaces are the most common cause of premature failure. Each bush is supplied with a polyurethane-compatible grease, typically silicone or PTFE-based, which must be used in place of standard rubber-bush grease, as the latter is chemically incompatible with polyurethane and will attack and degrade the material over time. The single most important fitting rule is that suspension fasteners must not be fully tightened until the car is back on its wheels at normal ride height, as tightening with the suspension hanging free pre-loads the bushes into a twisted position, and when the car is lowered the bush is already under stress, causing premature cracking and failure from the first journey. Squeaking is the principal service issue, typically appearing at the anti-roll-bar mountings or wishbone bushes after a few years, easily eliminated by withdrawing the bush, cleaning the contact surfaces, applying fresh grease, and refitting, as the squeak does not indicate a failure of the bush, simply that the contact surface needs renewed lubrication, with a periodic re-grease every two to three years keeping the bushes operating quietly.