Which will have longer lifespan: stock or urethane bushings?

Question

Background: this is in reference to the previously mentioned 2004 Subaru Impreza WRX Wagon. This isn't a track car: it's only for fun street commutes and general Daddy duty.

The car has upwards of 115K miles now and I'm hearing what sounds like aged bushing clunks and creaks coming from the rear suspension, especially at fairly low speed largish bumps and dips. I recognize that the bushings are consumable parts so I'm planning to replace the ones that I can do with hand tools and task out the ones that I can't.

So, here's the question: which type of bushing will have a longer lifespan, stock replacements or urethane "upgrades"?

I am very aware of the NVH price that must be paid with a full set of urethane bushings but I'm willing to consider it if it means a longer time between replacements. At the same time, a full set of stock replacements will also feel much better than the frankly weary parts that I have in there now.

Additional information on which bushings can definitely be replaced with hand tools, which definitely can't and which are on the borderline would also be appreciated by both me and future readers.

Answer 1

In my experience, Polyurethane bushes last longer than standard rubber ones, as the plastic doesn't perish in the same way that rubber does.

As you mention, there is a price to this, as they are generally harder than the equavalent OEM bushes, however many manufacturers offer a variety of stiffnesses, depending on the intended use - some of the softest ones aren't much harder than stock, wheras full race-spec ones will be. One caveat to be aware of is that the added stiffness of the Poly bushes will put additional strain on the other suspension components, which can lead to them failing through fatigue earlier than they otherwise would - In particular it is not recommended to use stiff bushes in some designs of trailing arm suspension for this reason.

As to which can be easily replaced by hand, a general rule of thumb is that any bushes that are pressed in to surrounding metal will need to be pressed out again, and thus will be difficult to do without a hydraulic press - though not normally impossible if you have a big vice, a 'suitable sized drift' and a big hammer! Any bush which is simple clamped in place by the component it is bushing should be fairly easy to replace.

Answer 2

I have had this on various occasions on all my Subarus once they get old, and on my Forester STi at only 70k miles!

• Polyurethane bushes on the much harder STi suspension last less time than rubber - it seems they are so hard the impact transferred to them is higher (have to replace every 25k or so - but this one is set up for track, despite being my commute vehicle)

• Polyurethane bushes on the stock suspension last longer than rubber (never replaced a polyurethane one yet once they are in)

If your one is set up for normal usage, I would suggest polyurethane will last longer.

I don't have any quantitative guidance on which are harder or easier to remove though.

Answer 3

Poly bushings last longer, and the car will handle better. As previously noted, the ride will be a little stiffer. As far as burning out the rubber OEM bushings, that's usually what you have to do if you reuse the shells; normally the case with polyurethane. OEM rubber bushings come with new shells and the rubber is bonded to the shell. If you have to burn them out, use a propane torch. In some cases you can spray a lot of WD40 on them and use a ball joint press to get the old rubber out of the outer shell.