[TR] What's the general life expectancy for rubber bushes for LBCs?
mdporter at dfn.com
Mon Apr 6 21:23:11 MDT 2015
On 4/6/2015 5:27 PM, Sujit Roy wrote:
> I changed them 14 years bac on my Stag This were the days before I
> heard about polyurethane.
> Are polyurethane bushes really fit and forget?
This is almost one of those questions that is never going to get a
satisfactory answer. We start with the presumption that the cars spoken
of are anywhere from 35 to 65 years old, and while the suspensions are
similar, they all behave differently from model to model, because of
engineering changes over time and differences in weight distribution,
roll rates, state of repair, general care, etc., and with a few
exceptions, the cars were bought used over a considerable range of time,
with no certainty of what had been replaced by previous owner(s) or at
All polymers--including rubber--have different rates of resistance to
deformation, typically a figure on the Shore durometer scale. The higher
the Shore number, the stiffer the elastomer. And, the higher the Shore
number, the rougher the ride, because the stiffer the elastomer, the
more road shock it transmits to the body and the controls. Typical
replacement parts were analogs of factory items, but that wasn't always
true, because of cost/supply issues, temporary shortages of oil or
natural rubber inputs, etc., depending upon when the replacement part
was produced. Compounding the problem is that factory and replacement
parts are subject to varying usages and mileage. A part that may have
worked wonderfully for twenty years on the car driven occasionally in
the summers by an enthusiast on well-kept streets will have failed in a
few years on a daily driver on rough roads.
So, choosing a replacement part today is pretty much dependent upon what
you expect to do with the car. Gentle driving, shows, etc., a standard
rubber replacement will do fine. If you are more demanding, some grade
of polyurethane may be more suitable. Even then, you should think about
the stiffness you really need. Too stiff and you'll find the car
unpleasant to drive. Too soft, and there's more deflection in the
suspension than you'll think wise. The advantage of polyurethanes today
is that they are a little less likely to degrade if soaked in oil,
compared to most mixed synthetic/natural rubbers.
Very generally, if you want to get out and drive the car with a little
vigor, I'd guess that anything of about 55-65 Shore is okay, whether
rubber or urethane. If you're going to baby the car, well, almost any
rubber replacement is probably okay, and will last a fair time as long
it doesn't become oil-soaked.
I put polyurethane bushings all around in my GT6 ten years ago, probably
of 75-80 durometer, and while they haven't degraded at all, from the
very start, the car felt like I was driving on cobblestones everywhere.
By contrast, I put new control arms (with rubber bushings) and struts in
the fourteen-year-old BMW last fall and the car is firm and relatively
silent going over bumps, and the braking shimmy is gone with new
bushings (definitely a problem with E39s), and the parts I replaced were
clearly originals, and had only started to present problems at the
12-1/2 year mark.
Everything wears. I doubt you're going to find a part on the car that
you can replace which will then last forever. Most grades of rubber are
probably better for comfort, and most grades of urethane/polyurethane
are better for stiffness, and will be subject to a little less
degradation from environmental attack. All that said, you should pick
the item that suits your driving habits and your intentions for the
Never let anyone drive you crazy when you know it's within walking distance....
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