Date:         Mon, 7 May 2012 17:56:08 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: Replacement for Steering Column's Upper Bolts?
Comments: To: jeff ensing <jeffensing@GMAIL.COM>
In-Reply-To:  <CAKW--nmLyNj3DV1Qdsp3DTdO=jmuLrNWOWnjh0EDn-wvKLu6CQ@mail.g
              mail.com>
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At 05:18 PM 5/7/2012, jeff ensing wrote:
>It is my understanding that these bolts are a shear bolt to aid in
>directing the column in an accident .

This was once a popular item of list wisdom, but it's been
demonstrated to be untrue, both by analysis of the forces and
structures involved and by asking VW.  It's a (pitiful, unless
thieves in Germany aren't allowed to carry Vise Grips) anti-theft
measure).  Plus VW sell them for something like USD12 each.

The column anticollision protection comes mainly in three
parts.  First, there's the flexible coupling between the upper and
lower steering column, shown as "flange" at the top of the list of
lower-column components on 48.2.  If the lower column is shoved
upward in a  collision the pins simply disengage from the coupling,
allowing the lower column to rise without affecting the upper
column.  Second, I haven't got a picture for it but you can see
fairly easily I think by taking off the panel cover.  Inside the
dashboard, the upper column mounting bolts bolt into a couple of
U-channel support straps going forward.  You'll see that these straps
are somewhat bent, so that if something pushes hard on them they will
collapse in a controlled fashion.  Thus these straps and the collapse
of the dash itself (or of the frontal structure of the van) are the
second line of protection.  The third line is the steering
wheel.  Its steel core is designed to bend in a severe collision.

The first measure prevents the column from becoming a spear or
bludgeon.  The other two provide energy absorption, allowing the
driver's upper body to decelerate gradually over the space of a
couple feet or alternatively to allow a certain amount of incursion
into the cab without the steering mechanism crushing him.  In order
for the second measure to work, it is necessary that the mounting
bolts *not* shear off.  The shearing referred to is the socket-head
drive section of the bolt which shears off when the anti-theft bolt
is installed.

Yours,
David