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

[Frank Swygert <farna@xxxxxxx>]

Tom, your fix is right on the money! I ran a 9/16" drill bit through the casting on mine, which knocked about 1/3 (maybe 1/2) the peak of the threads off, allowing a little more grease to get through. There's no stress on the threads, and even if it were drilled smooth the upper control arms would hold the trunnion in place. I like the idea of grinding/filing a flat on the pin though, that's a lot easier and can be done by anyone capable of taking the suspension apart. I also reassemble with anti-seize compound on the pin, so if it doesn't get much grease is still shouldn't seize for many years/miles. 

The ultimate fix would be to drill the casting and install an oil-lite (graphite impregnated bronze) bushing. The pin would have to stay threaded all the way in order to assemble the upper trunnion to the arms, but since there is no real pressure on the horizontal pin that shouldn't be a problem. Would make assembly easier -- no need to worry about centering! It would never seize and should be fine if never greased after initial assembly. Even after 100K miles there should be little (if any) wear. Never thought about this until now!! 

I do have one problem with your preventive-maintenance fix though. While the trunnion has little pressure on it, the spring does! The pivot pin is the only thing keeping the steering knuckle from pivoting in or out. If the steering knuckle pivots (and it most likely will with the pin out) the spring is going to fly out. The upper trunnion is NOT something to play with without removing the spring first! I was thinking if you could remove the bolt with the tire on the ground it might work, but then there is a danger of the steering knuckle pivoting inward. Less dangerous than if it pivoted out, but still a lot of potential to get seriously hurt or damage the car. The spring would be a lot of trouble to get back in too. Remember, the spring seat is offset to the inside -- the knuckle would most likely pivot in. The lower trunnion can be removed safely with the tire on the ground though. If other means are used to prevent the knuckle from pivoting in or out if should be safe, but
  better to remove that loaded spring! 


------------
Date: Thu, 06 Dec 2007 10:37:52 -0800
From: Tom Jennings <tomj@xxxxxxx>

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.

-- 
Frank Swygert
Publisher, "American Motors Cars" 
Magazine (AMC)
For all AMC enthusiasts
http://farna.home.att.net/AMC.html
(free download available!)


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