This is a quote from Sid (Drapal) He does a really nice dropped axle. He has been old skool trained in doing this. I figure he knows what he is talkin about.
"Glad to hear you guys like my axles. 3" drop is a lot lower then people think. You got to be careful because you don't want to be plowing pavement with your axle if you have a blow out. If you are running tall wheels then that's a different story. To figure out your scrub line. With your truck setting normal
1. Measure from bottom of axle to ground.
2. Measure from bottom of rim to ground (tire side wall height)
3. Now subtract #1 measurement from #2 this Equal srub line clearance
4. Now subtract from #3 measurement the amount of dropped axle you want.
Answer equals amount of clearance you have if you blew out your tires going down the road. YOU WANT CLEARANCE!!
If you guys ever need any help please get a hold of me and I do my best to help you out....SID "

52 GMC Suburban...52 Chevy 3/4 ton...49 CHevy 1/2 ton Rod...49 GMC 1/2 ton retro rod project