[200q20v] Delrin/ urethane bushing alternative

[Brandon Hull]

Thanks Bernie, I think it was your prior comments I was recalling re: delrin
etc.  As an untrained, amateur engineer, I have the few questions on your
response:  (and I should also add, I think this is a strictly track car
application)

> 1.  Low friction is not a critera.  You are purposefully and more
> effectively adding friction to the suspension system with the 
> hydraulic
> damper, the shock.

Two comments:  1) the primary goal is not low friction, it is zero
deflection for better suspension tuning accuracy.  2) as a secondary goal,
zero friction seems like a not bad idea because you want shock rebound to be
adjustable, and friction at the connection points is an unquantifiable
variable, which also probably changes over time.  in other words, if I'm
after precision damper adjustment, I'm better off with no friction at the
pivot point, no?

 
> 2.  Needle bearings require extreem concentricity and 
> parallelism accuracy
> of the bearing axes to achieve needle line contact rather 
> than destructive
> end point contact within the bearing.  To achieve this in an 
> A frame control
> arm system would require line boring of the A frame and a single,
> continuous, and straight shaft thru both bushings.  These are 
> the same, but
> much more demanding requirements than that of a good Delrin 
> bushing design,
> which has not been achieved by the aftermarket.  Impossible 
> in a single
> bushing arm such as used in the 44 chassis.

Yep, I see your point.  Although the Porsche application is in fact exactly
what you describe: the axis formed by a single long tube.  I notice also
from the pictures that the needle bearings are not just axial but radial. So
the precision you are after has to be achieved in two axis.  

Are you also saying that an a arm or wishbone flexes too much without the
tube you describe?  

 
> 3.  The application demands a bearing system having more than 
> one degree of
> freedom!  Such as a ball joint, or the stock elastomeric bushing.

Here I don't follow you.  Ideally the control arm would hinge precisely and
without variation, so that I could isolate the tuning effects of tires,
camber/caster/toe, and dozens of other variables.  I understand your point
if it is based on the realities of manufacturing variances which could be
resolved by, as you say, align boring the mounting holes, but optimally, why
the need for "greater than one degree of freedom?"

B


> Bernie
> 
> > From: Brandon Hull <brandon at cardinalpartners.com>
> > Date: Tue, 2 Oct 2001 09:31:55 -0400
> > To: "Audi 20V (E-mail)" <audi20v at rennlist.org>, 
> "s-car-list at egroups.com
> > (E-mail)" <s-car-list at egroups.com>, "200q20v (E-mail)" 
> <200q20v at audifans.com>
> > Subject: [200q20v] Delrin/ urethane bushing alternative
> > 
> > I happened upon this fascinating site today:  Shine Racing, 
> a VW tuner in MA
> > makes a needle bearing bushing insert for suspension 
> control arms.  The
> > advantage would be near zero friction in the suspension 
> movement, with zero
> > play.  (maybe a bad thing as has been discussed, if we assume mass
> > production engineering factors in some slop here to 
> accomodate production
> > variances)  
> > 
> > In any event, I'm curious to know if anyone has pursued 
> this for Audi
> > applications.
> > http://www.srsvw.com/basic.htm
> > 
> > A step by step Porsche installation:
> > http://www.all914.com/projects/ScottY/Part1/index.htm
> > 
> > Brandon Hull
> > eS2
> > 911SC
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