Those look like aftermarket overload springs (the shorter leaves on top.) They were designed to contact bumpers on brackets bolted to the frame after the main springs deflect a bit. The idea is that the truck rides like a stock suspension, but after the rear end squats a bit from a load, the second set of leaves engage to keep it from squatting all the way down to the frame bumpers. None were offered as stock springs for a '53 3100.


Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.