If the upper and lower arm do not describe perfectly parallel arcs, you will
experience this type of fatigue failure in the suspension because of the trunion
only having two axis of freedom, not three like a balljoint has. That's why
I've
given warnings before about not being glib in the use of shims to move the arms
for "proper alignment". If those two arms don't move in perfect parallel arcs,
binding must occur, and failure must follow.
"Pettis, Ward (NIDCD)" wrote:
> I'm doing a major rebuild of the front suspension. Before disassembly of
> the right side, I noticed that the A-arm would twist with the trunnion
> changing angle as I moved the stub axle back and forth. Strange, I thought
> until I found that the lower A-arm had separated at the weld points under
> the trunnion. No problem, ordered a used lower A-arm. Yesterday, I started
> putting the left suspension back together with new bushings, newly painted
> arms and a new trunnion. To my dismay, I noticed the same twisting action
> on the lower A-arm as I moved the stub axle back and forth! What's going
> on? Is this normal? If so, the separation of the weld points under the
> trunnion must be a common trait. Is it?? Or are both of my vertical links
> somehow bent out of line??
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