^ Very true. My only experience with rear ends was on an IH Scout a friend was working on several years ago. We decided to buy new gears and put them in ourselves. Keep in mind this is a big, ancient SUV/Truck type thing where everything is easy to work on.
The first full day with 3 guys on the project (none of us had done this kind of thing before, but we're all very experienced at any normal DIY mechanic stuff short of engine/diff/trans rebuilds, and we had a 2-post lift to work on) was a complete mess just learning what was going on during re-assembly, and realizing we didn't have enough of the correct shims, and that we had already crushed the crush bushing/washer thing for the pinion down flatter than it should be, etc, and that the one cheap dial gauge we had wasn't nearly enough in terms of taking repeatable measurements of the right kinds.
After ordering more bits and tools, we went back at it again for a full weekend (well, minus time spent drinking between) trying to get the thing reinstalled correctly. It was a long repetitive process of putting it in, seeing a problem with measurements and/or the grease pattern on the gears, pulling it back out and adjusting some shims, trying again and get wildly different results than we expected from the shim adjustments, etc.
Eventually we did make it work, but 3 guys x 3 days was totally not worth it vs just taking it down to a gear shop that does this stuff every day and paying them to do it right. Shortly after that I had to do a similar job on my '99 Trans Am. Dropped it off at a shop that specializes in diff/trans work and they had it back to me the next day working perfect for something like $500.
I'm all for encouraging people to take on DIY projects and do things themselves, because it's usually worth the learning process, but... if you're ready to tackle a diff install, you'd know it, and if you don't know it, don't bother
