Re: [Amc-list] early american front suspension

[Tom Jennings <tomj@xxxxxxx>]

On Tuesday 11 September 2007 06:51:52 Frank Swygert wrote:

> Hmm... never thought about the braking forces much! I had 7.7" tires
> (195 mm) and 79 Spirit disc brakes at the time one of mine worked loose.
> One didn't feel quite as tight as the others in the arm, but didn't turn
> or anything. I did stake it at a visible spot with a punch so I could
> easily see if it was turning. After a few months I stopped looking much
> since it never moved. Checked it weekly for 2-3 months though! Two years
> later things changed somehow. It was a rear cap, so the braking forces
> make a bit of sense -- load is taken off the lower rear when braking
> hard, I'd think.

I think what might happen at the lower trunnion is that the tip of the A-arm 
gets twisted during hard braking; the brakes try to rotate the steering 
knuckle, on the drivers side it wants to go counter-clockwise. The knuckle is 
a big lever with the fulcrum near the upper A-arm, and the load is the lower 
rear trunnion cap -- it's pushed back and upward, transmitting energy to the 
arms as twisting. (The trunnion pulls on the front trunnion cap.)

The shock spacer is the ONLY thing keeping the lower arm rigid! And I was 
gonna make a reduced-diameter spacer to accomodate a modern shock, but I'm 
not gonna do that any more -- in fact I think I will make a LARGER! diameter 
spacer as a strength member, and put the shock more inwards (there's a pair 
of extra holes in the lower arms about 3" further back). I'd rather have 
poorer shock absorbtion/ride than busted trunnions!
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