[AMC-List] '69 AMX front suspension change

[<francis.swygert@xxxxxxxxxxxxxxxxxx>]

The only difference for the front suspension is the shock towers. The
Mustang II type suspensions require a lot of cutting and welding due to
the way the upper arm is mounted. I've seen it done, but it's a lot of
work to do right. If you have access to a 70+ Javelin, AMX, or even
Hornet (or derivative) you may as well cut the spring tower out. The
Hornet type won't be an exact fit for the AMX, but the suspension mount
locations are correct.Cut and trim the Hornet panel then cut out what is
necessary on the Javelin. The upper part of the panel is the main
difference. If welded properly it will be as strong as a one piece
panel, but a little reinforcement along the weld seams (say a 2" strip
of metal welded in behind the seams, and along the edges) won't hurt.
Just don't get it to hot while welding -- that's the primary mistake
people make. You may know this already, but weld in 1/2" beads then skip
and inch and weld another 1/2". When complete allow the metal to cool a
bit (30 minutes is nice!), then start again. Takes three rotations, but
the metal has the needed time to cool between welds. Electric arc
welding ("stick", TIG, MIG, or flux core) brings temps up to over 1200
degrees at the weld, which sinks into the surrounding metal quickly. A
continuous bead is faster and looks better, but overheats the metal and
changes the composition in the weld area, making it brittle. NEVER rush
welding!!

But I have to ask why you want to change the suspension. You get some
built in anti-dive with the newer suspension, but that's the only real
benefit. Upper trunnions are expensive to replace, but the replacements
with poly bushings will last the life of the car with little
maintenance, unlike the original ones made with a softer, older
synthetic rubber compound. Or replace all the rubber with machined
bronze bushings (any machinist can make and install if you take them the
trunnion, upright, and trhough bolt). I've not noticed a lot of dive on
hard braking except on bone stock cars. Stiffer springs and sway bars
usually minimize dive on hard braking. Replacing the trunnions with a
poly or bronze bushed type will cost less and be less work than any of
the other two options. Even if you have a donor car sitting there and
can do all the cutting and welding yourself, there is a lot more work
involved for little gain. I understand not wanting to mess with the
trunnions again, but if done right with modern parts there will be no
need to. 

Most people want to replace the trunnions because they think they're a
poor design. That's not the case. Even the original rubber design lasts
as long as ball joints, mileage and time combined. The rubber does
degrade with time even if the car had only a couple thousand miles on it
when parked, so a 36 year old low mile trunnion will need replacing if
driven whereas a ball joint would just need some fresh grease. That's
rarely the case -- most older cars have been driven and the ball joints
are due to be replaced in 20-30 years. The original criteria design for
most cars in the 60s was 10 years or 100,000 miles before worn to
replacement for "hard" parts (not belts, tires, etc.). The rubber bushed
trunnions exceed that, but the poly or bronze bushed ones will go twice
that amount easily, and won't degrade like even modern synthetic rubber
formulas eventually will. Poly will eventually degrade, but not after 10
years unless they have come into contact with some type of incompatible
lube. Modern synthetic grease shouldn't affect them. The trunnion is not
an inferior design, just a different one. The auto world went to ball
joints because they were eventually cheaper and most importantly quicker
to install. There are more parts to a trunnion suspension and it takes
more time to assemble it, but that shouldn't matter now, since it's just
one car and only needs to be done once. 
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