a body lift are pucks that are installed between the frame rails and the body, on each body mount. Essentially it raises the body off the frame.
Suspension lift, as the name suggests puts in springs that raise the frame (and therefore the body) up, so that the distance between axles and frame will be bigger. This achieved by a bigger arch in leaf springs. Some suspension lits also use a bigger block in the rear, but the result is the same: a reloaction of the frame upwards.
That and there are also some other things that have to be done, lengthening linkages and such. Sometimes depending the truck the bumpers have to be raised as well. I just saw a F 250 that had a body lift on it and didn't raise the bumpers, looked like crap.
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