[Amc-list] early american front suspension

[Tom Jennings <tomj@xxxxxxx>]

Oh my, that is one *peculiar* system!

The upper arm contains the difficult trunnion that freezes into one solid mass 
of corroded iron. I solved that. The lower trunnion, a decent design unless 
NEVER greased, is just as weird.

Typical of AMCs others decent TSMs, there't not a single hint on how you 
assemble the thing. I have the big-car trunnion down to a science, but the 
American defies a simple assembly system.

The problem is that the control arm bushings run on a forged one-piece part, 
and not separate bolts like everything else. This means you have to assemble 
the arm halves onto the trunnion (lower or upper) after placing them over the 
inner pivots. (Which conveniently remove from the car.)

The uppers are only slightly annoying to assemble. The lower arm is just 
bizarre. I pressed in the bushings and fitted the trunnion nuts into the 
arms. To the lower trunnion I added the new O-rings, greased the threaded 
journals, and assembled the trunnion and lower arms, adjusting it so that the 
shock absorber mount/spacer just fit.

Then I clamped one arm of this sub-assembly in the vise so that the inner 
pivot will be vertical. Of course you can't put the pivot bar in; so now take 
the trunnion nut (1-1/8") out of the top (unclamped) arm, put the inner cup 
washers and pivot bar in place, then the arm, and inserted the shock spacers 
with the bolt very loose. 

Now comes the tricky part -- getting that last trunnion nut on. As assembled 
in the vise, the threaded end of the trunnion is protruding from the arm. 
This part is all feel and judgement and danger. The trunnion nut threads onto 
the trunnion, but at some point it contacts the arm. The nut's external 
threads are really broad and shallow an thread into the arm. Cross-thread 
this, and you ruin the arm. But you have to thread two different-pitch 
threads at once! And in doing so maintain the exact spacing between the arms 
for the shock spacer. 

Basically I pull up and pushed down on the arm (slight flex) to feel the start 
of the external thread. Once caught, it goes OK. Caught wrong, it wants to 
cross-thread. 

I got it right but it pretty much defies explanation. The nice thing is, the 
whole suspension except spring can be assembled on the bench, it weighs about 
20 lbs without the brakes, and bolts into the car with four bolts! That part 
is sweet.

Somehow it all works, and it's very pretty when done. It's a very spare and 
elegant design in it's own way. The inability to lube the thing is the only 
serious problem, and I think I fixed that.

I'll take pictures when I do the other side this weekend.
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