Build up some heavy wood blocks under the frame rail, put the jack on the blocks and raise the frame until you have no weight on the tire. With a second jack you can raise the axle away from the spring after removing the shackle hardware. I would use some heavy jack stands or block the frame with 6x6, 4x4, whatever lumber you have to build a crib under the frame.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
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