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measure from the shackle bolt to axle tube,see if they measure the same from side to side.maybe the tire was hit hard or ran into something and shift the axle tube on the spring,not likely with a center pin ,but with enough impact at sometime, anything is possible.
might be that its the brake line going from the frame to the caliper cause my old dually pulled like a demon to the one side so if its not the axles moved might want to try that
yeah the problem i was told was that with the age the brake line actually collapses on the inside so its harder for the pressure to be released causeing the brakes to stick on that side
Your toe angle is 0° then get an alignment from a reputable shop.