[ba] replacing sub frame bushings

Trevor Frank tfrank at symyx.com
Tue Aug 19 17:13:47 EDT 2003


-----Original Message-----
From: Wyatt's Dad's Audi [mailto:audion at serversmiths.com]
Sent: Tuesday, August 19, 2003 11:36 AM
To: 'ba-audifans'
Subject: Re: [ba] replacing sub frame bushings

On Tuesday, August 19, 2003, at 09:46 AM, Chris Maresca wrote:

> Maybe, but the Delrins just makes that fact worse.  As evidenced by
> fact that all the cracked arms were Delrins...

I'll wade in here since I started the topic and know somethings about
energy transfer.

I was in the high end audio biz for many years and there we dealt with
energy on the microscopic level and the benefit was that you could see
principles at play in a small space.

So, the upshot is that energy cannot be created or destroyed but merely
transferred onward. That means the energy that was being put into the
suspension was being dissipated in the bushings by the movement of the
bushings as they transferred the energy into heat. With Delrin that
work can no longer be done as the joint is now "snug" (hence the better

So the energy moves on and finds *the next weakest link* and starts to
do work there by flexing the A arms and finally cracking them. The
important point here is that after you weld up your arms so they won't
crack, the energy just moves on to the *next weakest link* and starts
working on that point in the chain. Where is that point? What will
happen if(when) it fails? Many good designs factor in a weakest point
to allow for the energy to dissipate and when you eliminate that
weakest link you are off on your own.

I ask these questions of myself and my riding buddies when we discuss
improving our motorcycle suspensions as on bikes we don't get quite the
error factor that we get in cars. Crack a frame member and you might be
in the weeds at 60+ MPH.

So, thanks for all the feedback about bushings, I'm 99% sure I'm best
off chasing down some stock units and just getting back to a nice level
of OEM tightness and saving the time and dough or a nice tweazy rear
shock for my bike.

BTW, I'm on a large number of mailing lists on a wide range of topics
and this little BA Audi list is probably the most useful with the
lowest noise level. All I have to do is figure out why I'm getting
double posts on everything.


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