[200q20v] Delrin/ urethane bushing alternative

Bernie Benz b.m.benz at prodigy.net
Tue Oct 2 12:38:41 EDT 2001

> From: Brandon Hull <brandon at cardinalpartners.com>
> Date: Tue, 2 Oct 2001 12:29:39 -0400
> To: "'Bernie Benz'" <b.m.benz at prodigy.net>, Brandon Hull
> <brandon at cardinalpartners.com>
> Cc: audi-20v <audi20v at rennlist.org>, 200q20V mailing list
> <200q20v at audifans.com>, s-car-list at egroups.com
> Subject: [200q20v] Delrin/ urethane bushing alternative
> 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?
No.  Insugnificant by orders of magnidude.  You are arguing about small
changes in friction in a journal having a 1/4" radius as a lever arm vs.
a hydraulic damper operating at a 15 to 18" radius.  Perspective is all
>> 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.
The single shaft solves the shaft axes congruency problem but that is only
half of the solution.  The housing axes of the two bearings must also be
congruent, requiring that the A arm be line bored.

> 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.
Wrong two axes.  Radial needle bearings on the same shaft would only control
A arm end play, a trivial concern, and not requiring antifriction bearings.
The second degree of freedom must allow for noncongruent A arm pivot axes.
> Are you also saying that an a arm or wishbone flexes too much without the
> tube you describe?
No.  The system under discussion is a single degree of freedom, seperated
two bearing system in which neither bore axes nor shaft axes are congruent.

A arm flexure is another unrelated problem, possibly compounding or easing
the bushing system problem.  (If they flexed enough, they wouldn't break.)
>> 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?"
I've defined the system above.  If you can't see and understand the compound
congruency problem, just believe.  It's real, and it breaks A arms when the
wrong bushings are applied.

>>> 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
>>> _______________________________________________
>>> 200q20v mailing list
>>> 200q20v at audifans.com
>>> http://www.audifans.com/mailman/listinfo/200q20v
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