[TR] When to change rubber bushings

[Jerry Van Vlack]

I know a little about rubber components as I sold them to the OEM's for the
last 20 years and I did stay at a Holiday Inn Express on several of my
business trips!

Others have said and they are correct, that there are many different
compounds as well as polymers to choose from when developing a rubber part.
Ideally you start with a set of performance parameters such as temperature,
fluids, dynamics and environmental conditions before your design a rubber
part. Each of the synthetic polymers as well as natural rubber do well or
not so well in specific applications. Natural rubber is the best for dynamic
applications such as engine, transmission, suspension, differential or even
wiper motor mounts. It's not so good around oils and fuels. When our cars
were made the engineers selected available polymers for specific
applications and then had parts designed for those applications. Designs
took into account cost as well as performance. Other synthetic polymers such
as EPDM are excellent for Ozone resistance and are used in window and door
trim areas or perhaps truck seals. Nitriles are generally good for oils and
greases and with each additional performance constraint came added costs.
Today compounds can range from pennies a pound to several dollars per pound
for the ones needed to withstand high temperatures or very aggressive
fluids. I could go on but hopefully you get the general idea of how a
particular rubber polymer was selected and are still selected for automobile
applications. Many times two different chemists will arrive at a compound
formula that meets the performance requirements but have significantly
different costs. In today's automotive world cost is the driving factor and
sometimes takes priority over performance much to the disgust of the
engineer and chemist who worked so hard to develop the right parts.

Moving to our parts (or any collector car parts) made at relatively low
volumes for a small group of consumers and by folks both in the US and
overseas the cost becomes even more important to the small group of
suppliers. I will guess that original drawings or material specifications as
well as performance criteria are long gone and now the production of parts
is left to trying to duplicate dimensionally some old stock part and the
selection of an appropriate compound and polymer is left to the supplier to
decide based on very little performance criteria. Couple that with little or
no actual testing as well as sourcing in some 3rd world nation it doesn't
surprise me that we get what we get when it comes to rubber parts made for
our cars.

JVV

----- Original Message -----
From: "Nolan" <foxtrapper at ispwest.com>
To: "Triumph Sports car discussion" <triumphs at autox.team.net>
Sent: Friday, July 20, 2007 11:40 AM
Subject: Re: [TR] When to change rubber bushings


> One of the things I've always found interesting with rubber bushings and
> gaskets is the vast difference in the oem quality.  European cars have the
> absolute worse.  They tend to start falling apart after just a few years.
> At the other end are the American cars.  Those last for forever it seems.
> The Japanese cars are pretty good as well, but they don't survive rubbing
as
> well as the American rubbers.
>
> As for aftermarket replacements, I've had them fail as I'm installing
them.
> It's quite annoying to watch a new tie-rod end boot split as you're
> installing it.  Some were better, and lasted to the end of the week.
India
> and Israel sourced pieces seem to be the worse.
>
> As for our Triumphs, I mostly wish someone would make oem equivalent
pieces,
> not sorta-equivalent pieces.  Especially when it comes to things like
window
> scrapers and the like.  As in flocked on the inside so they actually slide
> on the glass, and rounded edged, not square that feels sharp under your
arm.