Re: [Amc-list] 'Flexible Flyers' con't

[Tom Jennings <tomj@xxxxxxx>]

On Wed, 2007-07-04 at 09:03 -0400, Brien Tourville wrote a bunch of
stuff:


> Snip - Gotcha' .  The 'pressed metal' Upper Control Arms where
> the bushings press in isn't that much more 'Awe Inspiring' than
> the lower control arms.  
> 
> Making the bushing insert 'tube' out of
> something thicker walled would make me feel better. 

The upper control arms have nearly all forces constrained to vertical
motion. The only non-vertical force they receive is when the lower arm
moves fore/aft (eg. hit the brakes HARD or bonk a curb) which would move
the lower ball joint/trunnion rearward, which would torque the upper
joint with a long lever, twisting the trunnion and therefore the arms.

(You could argue that an upper ball joint is superior if the only thing
it did was not transmit torque from the steering knuckle to the upper
arm, since it is free to move in any direction except up/down (the
balljoint guts that is).)



> Snip - So if I have the upper and lower control arms crafted out
> of Hi-Strength Tubular Steel - it will accelerate the Failure Rate
> of the Bushings / attachment points ?

Upper arms with a ball joint -- doesn't matter what you do within
reason.

Lower arm, if the arm can't twist longitudinally then all the energy
driving that rotation has got to dissipate somewhere!

That lower arm twists A LOT! It has to -- ignore the inner bushing for
the moment -- consider that the balljoint rides on the end of the strut
rod anchored in the chassis a mere 16" or so away. That's a 16" radius
circle. That means for a 4" vertical travel of the tire and wheel, the
balljoint-end of the lower arm rotates about 14 degrees. If you make the
lower arm super-stiff you'll break something.



Americans as a car market have never cared about handling performance,
for the most part. Horsepower and the drag strip were it, and style.
They were engineered for low cost and safety first. AMC had it's own
peculiar form of engineering conservatism that I personally like a lot.
I love the slow evolution and the frugality that means we have so many
interchangable and adaptable parts. 


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