Re: [Amc-list] Early American Front Suspension

[Frank Swygert <farna@xxxxxxx>]

Tom, great work (as usual) on your site documenting the assembly of the 
58-63 American front suspension! It will be a reference from now on for 
sure. It is a bit of trouble to get everything lined up when putting the 
lower trunnion together, but I didn't think it was that hard! No, it 
doesn't just bolt together with no thought like a ball joint, but not 
real bad!

The lower arms are exactly the same as 58-61 big cars. They have 
different part numbers because the only way AMC sold them was with the 
inner bushing pressed in from the factory. you could buy just the 
bushings, but I guess they figured if you needed an arm you weren't 
going to press an old bushing out and reuse it! The big cars use a 3/8" 
bolt through the bushing, the American has 5/8" (IIRC) mounting bar 
ends. Change the bushings and the arms interchange.

The upper arms can't be interchanged, and you can't use the big car 
trunnion even if you shortened the arms. Look closely at the spring 
seats on both. The American (remember everyone, we're talking 58-63 
here!!) has the spring seat offset to the inside, the big car spring 
seat is directly centered above the trunnion. The spring seat on the 
American is also much closer to the pivot point. To top it all off, the 
horizontal pivot point for the upper arms is to the OUTSIDE of the 
vertical pivot point of the steering knuckle, moving the spring to the 
inside even further. The lower end of the spring is about centered on 
the tire sidewall, with maybe two inches clearance with the stock 6" 
wide wheels and tires (wheels might be 5.5"). Wider wheels and tires 
move it even closer. The ends of the upper arms are about even with the 
outer rim of the wheel, and the stock spring seat location is positioned 
so that the spring is pretty much vertical, maybe with a slight inward 
tilt. Moving the pivot point further out would hit the tire and mess up 
geometry (especially vertical location in relation to the spring). It's 
just not feasible!  The upper arm position is about the same on the big 
cars and American in relation to the wheel edge, but the tall spring 
seat of the big cars put the edge of the spring ABOVE the tire, not 
BESIDE it!

The trunnion itself could, however, be replaced. The cast body for the 
upper trunnion didn't appear until 1954 or 55 in the Nash Rambler. I 
don't have the 53 and 54 TSM supplements to determine which year, just 
the full 52 and 55 Nash TSMs. Before that there was a two piece 
trunnion. The srping seat was similar to the 58-61 big cars, but much 
shorter. It screwed onto the top of the trunnion just like the big cars. 
The trunnion was a "crossed tube" affair. It looks similar to two pieces 
of tubing crossed in the center, one on top of the other, then welded 
(it appears to be a casting though). The vertical piece is on the inside 
in relation to the horizontal piece, just like the one piece casting of 
the 58-63. I'm not positive the 50-53 (or 54) trunnion will fit the 
steering knuckle of the 58-63, but it would be easy to take two pieces 
of tubing and weld them in the correct positions, then make bronze 
bushings for the horizontal and vertical pins. Use oilite (self 
lubricating bronze bushing material -- graphite impregnated bronze) and 
you really wouldn't need a grease zerk on a smooth horizontal pin (head 
on one end, threaded on the other to keep it in). The upper part of the 
tubing would need a spring seat a little more inboard than the big car 
spring seat. The outside of the top of the vertical tubing could be 
threaded and a 58-66 big car spring seat modified to fit though. The 
spring seat could be welded in place, just cut a hole above the vertical 
pin so a deep socket could be used to remove the nut.

The above may sound crazy, but Pierre Beauchamp (the Canadian 
performance AMC guy.. think I have the name right!) made a replacement 
trunnion for the 68-69 Javelin and AMX just as I described. I'm not sure 
it's available any more. He used a coil over shock in place of the 
original spring.

-- 
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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