[Amc-list] early American upper trunnion bolt, revisited

[Tom Jennings <tomj@xxxxxxx>]

It's been a few months and a few thousand miles on my home-made
upper trunnion parts for the 63 American and it's been behaving
perfectly.  Without complete disassembly it's impossible to
look at how grease is distributed in the threads in the upper
casting, which is the critical thing, but it's done nothing
stupid like loosen, rotate, deform, etc. Since the critical
mechanical area is where the trunnion pivot parts (stock bolt
and nut, or stud and double-nuts on mine) meet the stamped arms,
that's easy to inspect.

I've given further thought to this system and I think there's
a couple of easy fixes to make the stock part work fine, and if you have a 
totally stock part installed, a way to extend it's life probably 
indefinitely.


The problem of course is that the lubrication system for the
early American upper trunnion is worthless. It's pretty much
impossible to get grease through the tight threads when it ages
(10? 20? years? 50K? 80K? miles), at which point the bolt seizes
to the casting, ruining the upper arms; extracting the
seized bolt is extremely difficult (the hardest bolt extraction
I've ever done).


The stock bolt is drilled lengthwise, with one small
cross-drilled hole intended to feed grease to the middle of
the thread. It's a joke. However, simply filing a flat on the bolt,
lengthwise, such that the flat passes over the cross-drilled
hole, will allow grease to flow up to the head and tail of
the bolt. That's pretty much all that my fix does. With a
double-"D" 'd bolt grease would at least extend down the length
of the bolt, in an "H" pattern. It still doesn't gaurantee that it gets to 
the threads to either side of the flat but would lube a lot of area within 
the casting as the suspension works up and down on the road.


A preventiative-maintenance fix for that I think is to partially remove the
bolt every year or two or three: remove the wheel, jack
the lower A-arm (2x4 wood behind the lower trunnion) so that
the spring isn't resting on the upper stop. Remove the nut,
and back the bolt out until it's just barely threaded to the arm.

As you screw the bolt back in, grease it a few times. This should
re-distribute grease along the entire length of the casting
threads. Install the nut and torque as usual.

It's not as difficult or extreme as it sounds; with the lower
A-arm supported there's almost no force on the upper arm, and the
upper trunnion bolt is easily reachable with the tire off. It's
probably 30 minutes per side, and would likely extend the life
of the upper part indefinitely; there's really nothing else
up there to wear, if the bolt doesn't freeze it would probably
last 200,000+ miles without repair.


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