Cheap lowering springs for trunnions

My mistake was that the 975lb figure was the corner weight, not the front end weight. These cars are light, but they aren't that light!

That makes the original HD spring 18.3" long, and the 13" circle track springs line up with DAMX's original figures.

I'm thinking of going with the 200lb/in springs, but I need to measure my car to see how much drop would make the lower control arm level with the ground. I think it would be around 1.5-2 inches, but that is just from eyeballing it.

There are 11" springs that are also widely available, if someone wants a really stiff spring, but they're short enough that you'd need to limit travel to make sure they don't fall out under decompression.

 I'm going to stick with the 13" springs, especially because I'm not building a car for competition.

Like you said, these numbers are just for the trunnion cars. Since the spring on the later models attaches partway up the UCA, it would have some motion ratio other than 1:1. Makes it easier to go to coilovers, though!

I'd love to upgrade to the Dairyland setup and ditch the trunnions, but that will have to come later when I don't have as many other projects going on. So, circle track springs for now, and leave the rest alone.

Everyone wants to ditch the trunnions, I hear that all the time!

There is nothing wrong with trunnions. The rubber isolated type as used in the 64-69 American/Javelin/AMX are the most talked about, but those were used in Trans-Am racing early on, as well as baby NASCAR in 68-69. They handle well as long as they are in good condition -- mostly meaning not 40+ years old. Everything, even ball joints, wear out and deteriorate with age! The rubber (actually a neoprene blend, not really rubber) bushing inside the small car trunnion eventually wears. Replacing it with a polyurethane insert changes the way the insert works slightly, but is a huge upgrade. It costs more to replace the suspension with something else than to rebuild the trunnion with a poly bushing in the upright. It's not modern, but it works great.

The ONLY drawback to the AMC trunnion suspension (any of the three designs) is that you can't get much additional caster. If you go over 2-3 degrees caster the upright (steering knuckle) can bind. There is some caster built into the front suspension, but not much. These cars handle best at zero caster. I've run mine at zero and at the max of three degrees -- it tracks best at zero, adding the three degrees didn't seem to help any. Caster helps with tracking straight and returning to straight after turning, doesn't help turning itself. Again, the three degrees didn't seem to make a noticeable difference, and overall handling seems to be better at the factory zero degree cater specification.

I'm going to disagree with you on the moving the spring inboard improves handling. A shorter spring... well, yes -- only because it's stiffer. The further inboard the spring the LESS leverage the tire has on it as the lever arm is shorter. As noted, directly over the steering point more anti-roll -- due partially to more leverage.  A 69 and 70 Javelin are virtually the same car, and the suspension geometry is virtually the same, except for the ball joint and required spring placement. The 70 spring is much stiffer than the 69 even though the dimensions of the spring are close to the same. Some companies have condensed part numbers and list the springs as interchangeable, but anyone who has put a 70 spring in a 68 or 69 has noted that the front end sits up much higher and the ride is harsh.

A tall spring allows more travel, and with rural road conditions of the late 40s/early 50s a lot of travel was needed. As we entered the 60s roads in most areas improved and the need for lots of travel on a street car diminished. Car hood and roof lines also got lower, which demanded lower mounted and therefore shorter (if you were going to keep them above the upper arm) springs.

I installed stiffer springs on the front of my 63 American (12% over stock) and handling improved dramatically. I also installed a roll bar, but it was hardly noticeable, whereas the stiffer springs were immediately apparent. I believe I hit a good compromise between ride and handling with 12% stiffer springs. You can just start to feel the harder ride, but it's not too hard even on rough roads. Noticeably harder on rough roads and every time you hit a pot hole for sure, but not overly so. Factory HD springs were 18-20% stiffer and definitely ride very hard -- like an old HD pickup -- too hard. I was afraid 10% wouldn't be enough, but 15% might be too much, so went for the middle and won.