At 09:01 AM 5/26/2011, Rocket J Squirrel wrote:
>Where might these control arms be illustrated in Bentley? I did not
>find them on 40.2 or 40.7, nor could I find them in Section 48
>(Steering) so there must belong to some other category of
>functionality in the vehicle.

You were tired.  The large part at the top of 40.2 is the upper
control arm, so labeled, and the large part at the bottom, the one
that changes from stamped to cast, is the lower control arm, also
labeled.  The steering knuckle with its ball joints is somewhat
hidden behind the hub/brake disc.

The inner ends of both control arms are mounted on the body, thus
forming a parallelogram completed by the steering knuckle, which has
ball joints top and bottom since it requires two degrees of freedom:
up and down, and rotation around the vertical axis.  It incorporates
a small protruding lever which carries a smaller ball joint securing
the end of the tie rod which goes to the steering rack.

The upper control arm has a wide base so its outer end is firmly
fixed in the fore-and-aft direction (it's equipped with eccentric
washers to adjust the end in or out, thus controlling camber).  The
lower arm however has a narrow base with a rubber bushing allowing
the outer end to swing forward or aft.  The strut bar positions it to
slightly trail the position of the upper arm.  This is the caster
adjustment, and it is what makes the steering self-centering.  If
caster were negative you'd have to actively hold the wheel in center
position at all times as it would prefer the extremes.

The three alignment adjustments are thus:

a) camber - the tilt inward or outward of the top of the wheel
measured in degrees; it's adjusted by moving the upper control arm in or out.

b) caster - the angle of trail of the steering axis, in degrees;
adjusted by lengthening or shortening the strut bar

c) toe - the degree to which the fronts of the wheels point in toward
each other, in degrees; adjusted by lengthening or shortening the tie rods.

Yrs,
David