[sweetk30]

med and heavy trucks dont use shackles like 1ton down . the back end of the leaf slips back/forward in a hanger is all . so if you tried to put in a narrower spring pack it would give side to side play and make things move in a bad way .

pics from my 88 gmc 7000 / chevy c-70 dump truck with 66k original miles

1 = front hanger front spring bolt in to hanger

2 & 3 = rear slip hanger spring rides in and a bolt holds in on the bottom from just droping out if lifted up .

4 = rear spring front hanger . upper is slipper and lower is tourqe spring holding the axle square .

5 = rear slipper with safety bolt like the front .

now i hope this helps understand why some trucks you cant just put narrower springs in and shim them easy .