They bolt to the spring pack. Basically you unbolt the u-bolts and jack the truck up off of the axle. Put some c-clamps around the leaf pack and remove the center pin. Remove the c-clamps and install the add-a-leaf wherever the manuf. tells you to put them in the pack and put the c-clamps back on to hold the pack together. Install NEW center pin in there and tighten it up. Bolt axle back to the springs and lower the truck and off you go with your new harsher riding yet slightly taller truck.
they go inbetween the the helper leaf and the 2nd leaf in the pack. Jack up the rear of the truck, takin all the weight off the tires, undo the u bolts, clamp the leaf pack, undo the center bolt in the spring pack, remove that bolt, undo the clamps, put the AAL in with the helper leaf (should be a flat leaf) under it, put the center bolt back in and tighten it back down, place the bolt back in the spring perch hole, put on new u-bolts, and then take the truck off the jacks...it may be easier to take the whole spring pack off the shackle and hanger...and clamps can help out too...i have done it on the front and rear of my truck, and the rear of a dakota, so its not that hard. You may have to push or even kick the axle back in place and jack the truck up really high to get the new bolt all the way in...another thing that helps is to take the tire off and place the axle on a low jack stand...thats about all i can think of to help you out...if u have any questions, IM me on AIM, the SNs RedneckDixieDude.
Edit: Jason covered it pretty well too...i could tell my truck was a lil harsher to ride in...but with the new shocks and everything, i LOVE the ride of it...don't ask why, but it rides really nice to me...another thing...the center pins in older leaf packs can be a pain in the ass to get out...hacksaws work, and a good pair of vice grips help out too...soak the u bolts and center pin with some penetrating oil if the springs have seen a few years, that helps out a lot...
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