This works...
Its a toss up--taking the spring off takes time,might waste the U-bolts,etc--you CAN change bushings on the vehicle--getting the bolts out of the bushings has been my biggest challenge,especially if your lacking a good cutting torch!--one method I've used with good success is to take the nut off the bolt,then if the bolt wont come out easy,grind the head of the bolt off with a grinder,or a sawsall,then stack some washers on the nut side and tighten the nut(make sure you have at least 3-4 threads into to nut so it wont strip the threads!)--as you tighten the nut,it will suck the "headless" bolt thru the bushing!--once it pulls in even slightly,they usually come right out,after the rust bond gets broken--this works best with an impact..
To remove and install bushings,two sockets or peices of pipe the right size along with a peice of threaded rod works in most cases-(similar to removing a U-joint-one big socket,one smaller)-but sometimes complete destruction of the old bushing is the only method to get them out--pressing them in this way usually works good,just lube the outer steel sleeve with grease or oil before pressing them in..
.I've done them without pulling the springs,the frontmost bushing on the front springs are the worst!-(many trucks had the "EYE" of the spring openned up and the bushings just flopped around,and needed new main leafs!)-the shackle end never seems to have seized bolts,those 7/16 bolts dont seem to rust up as badly as the bigger bolts on the other end,or on the rear springs!--(and I've NEVER understood how those 7/16 bolts hold the weight of the whole truck,winch,plow,etc,without snapping right off!
