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If you need to replace your classic’s clapped out suspension bushes, then why not go polyurethane and make it even better. But is it really that simple?

Ford had a term for it more than 50 years ago – NVH, standing for Noise, Vibration and Harshness. And it was these three factors it wanted to eliminate and help rid its models of that Dagenham Dustbin image. Jaguar, on the other hand, simply wanted to create the World’s best saloon in terms of comfort and refinement with its XJ6 but without spoiling the superb handling that comes with the Browns Lane badge. What’s the connection? Suspension bushes!

Without these small innocuous components, your car would feel like a cross between a go-kart and a tank to drive. Compliance bushes, as they are also known, provide the essential cushion between the suspension, steering, chassis and bodyshell. Too firm and the car will feel extremely precise but too harsh. Conversely, too soft and the handling and roadholding unduly suffers. As a result the car makers have to walk a fine line to achieve the best compromise. But thanks to polyurethane bushes, you can now improve on what the factory fitted.

WHY PICK POLY?

There’s several logical reasons, both concerning performance and practicality – let’s start with the latter. Being synthetic, they last a heck of a lot longer than original equipment rubber and are also impervious to contamination; manufacturers say that they are fit-and-forget so it’s a cost effective one-off expenditure.

Historically, polyurethane bushes have been seen as a performance upgrade and only suitable for performance cars. However, in recent years an increasing number of people are fitting them as a straight replacement option on regular daily driven road vehicles, so says leading exponents Powerflex.

“Unfortunately when polyurethane was introduced into the automotive industry you had companies with little experience using poorly formulated, cheap polyurethane that meant for a harsh and squeaky ride, not something someone would want for their normal road vehicle.

“That misconception and, view of polyurethane bushes, has been hard to shift but we are fortunate to be one of those companies that have helped dispel that myth by manufacturing using quality materials and producing a quality premium product that isn’t too harsh and doesn’t squeak,” says the company, adding that it’s the cheaper types which are to blame for the misconception that all polyurethane bushes on the market are harsh and noisy in operation. Indeed, with older cars replacement bushes may not be available so PU offers a good alternative.

Certainly, when Classic Motoring has used quality replacement polyurethane bushes in the past we haven’t noticed any increase in noise or marked deterioration of refinement.

From a performance perspective a poly bush will tighten up the chassis by removing unwanted flex in the suspension and steering assemblies and so provide more feel and precision. They come in various states of firmness (rated in ‘Shores’) allowing an owner to choose between handling or comfort. Make no mistake, renewing the bushes on your oldie will reap rewards if for no other reason that rubber bushes degrade so gradually that you may not have noticed any deterioration – until you get the chance to drive an identical make and model that’s been overhauled in this department says Polybush.

In fact, some specialists recommend this modification (if it can be called that) as the first step to improving a classic, especially if you also opt for a harder type as it can help compensate for ‘relaxation’ of the body and chassis structure which inevitably occurs over time.

WHICH ONES TO FIT AND WHERE?

There’s several different types of bush. First off is a straight like-forlike replacement and this is the most popular type say most makers. Above this is the fast road or ‘Touring’ alternative which is notably harder for better precision and yet without unduly hurting comfort and refinement, unlike track/motorsport types which are very much a no compromise bush.

For the vast majority of motorists, the standard and Touring bushes are the best bet because track types are really much too harsh and uncompromising for normal drivers. According to Powerflex, a correctly formulated polyurethane is as good if not better at noise, vibration and harshness suppression when compared to worn rubber ones. At the other end of the performance scale, its Black Series bushes are manufactured using Black 95 Shore, to provide maximum control of chassis geometry. This compound can be up to 80 per cent more resistant to load than standard rubber and 25 per cent stiffer than the company’s regular performance material.

Polybush [the company] markets three levels, performance (the stiffest aimed at track driving, Dynamic (fast rod) and Comfort, which unlike the others is not coloured red but a blue/purple and are normal types, so don’t always go by colour as an indication of their performance and hardness. Superflex says its default colour is now black. “There are still some dark blue bushes in our range which are being phased out,” it told Classic Motoring.

Where you uprate depends upon your desires and the classic you drive as they all differ and this is why you should consult a marque specialist first. For example, Jag XK experts Bristol Classic and Sports Cars prefers the Australian Superpro because, it says, unlike the others it has tried, offers the ideal compromise for this particular chassis.

Virtually anything where there’s a compliance bush residing can be polybushed; anti-roll bar mounts, subframes, wishbones (a very common replacement on modern classics), steering racks, strut top mounts… the list is ever expanding but there’s no need to automatically opt for a performance replacement. Chris Witor of Superflex told us; “Some bushes will make little or no improvement to handling eg: spring insulators, whereas replacing worn bushes at key locations eg tie bars, compliance bushes, control arms and trailing arms will get rid of some quirkiness in handling”.

Typically, you can mix and match the shore ratings but what you must do, always, is replace in pairs or axle sets otherwise the handling will be severely affected. Don’t go too firm on an oldie warns Superflex as a track-hard bush (95 Shores) fitted where some ‘flex’ is needed “could indeed cause metal fatigue and possible car component failure” although no other company we contacted agreed with this rather worrying comment.

Once the suspension is uprated in this way then ideally the chassis and steering alignments should now be checked and adjusted, if need be.

NO PAIN, NO GAIN

Polybushing is a really worthwhile fit but it don’t come easy! Fitting them can be a real swine simply because most old bushes will be worn and seized in their housings and only brute force, cutting and in many cases heat may be the only way to get them out. Also, as in the case of subframes, you may need to remove these assemblies from the body and for this reason it’s imperative that the car is raised and supported properly. Special pullers are available either for purchase or hire and they make the job a lot easier and safer, but you can also get away using normal tools plus you can successfully make a half decent removal tool out of something little more elaborate than studding, washers and old sockets (see our fitting pic strips).

We’ve yet to remove an old bush that didn’t need persuasion and for this reason you may wish a garage or specialist to do the job.

Prices are dependent on what type you fit, and where, but beware of cheap substitutes or imitations of quality ones warn the major, better known manufacturers because they just don’t perform or last like they should and are a false economy.

Talking of which – how much does it cost? Well, it depends how far you go; for example, an anti-roll bush set for an MGB or Midget starts off at less than £8 with complete kits for their front and rear suspensions at under £70 while on ‘moderns’ VW Golf anti roll bar bushes sell for less than £20. On the other hand, going the whole hog, with professional fitting, can run into four figures. Bite the bullet and break the bank because it’s not only money well spent but also the best budget ‘mod’ that you can carry out on many classics.

Don’t take our word for it though, just ask leading experts such as Revington TR and TR GB, who both say that a complete re-bush kit on that much-loved IRS Triumph sportster will transform the driving quality of many TR4-6s like you wouldn’t believe (all for around £500 or so) simply by making it feel like brand new again.

SHORE SAVVY

TO GIVE YOU SOME IDEA OF THE DIFFERENT TYPES AVAILABLE AND WHERE TO FIT THEM, HERE IS POWERFLEX’S GUIDE ALONG WITH THEIR SHORE RATING AND COLOUR CODING

Red 65A Used for Universal exhaust mounts and diesel engine mounts where some flex is neded to prevent harshness Yellow 70A A slightly harder grade, this is used for engine mounts, differential and subframe mounts or areas where the bush needs a lot of movement and absorption

Purple 80A Powerflex’s most common material. This is used in most areas of the suspension and provides the right mix between performance and compliance

Black 95A The company’s hardest material. This is used for its Black Series range or on normal road vehicles where the vehicle’s suspension assemblies demand this hardness of material i.e. in areas of high load