One of the best examples of this is a Chevy pickup dashboard. To change the AC evaporator core EVERYTHING has to come off, right down to the metal. The entire dashboard is removed. This takes hours of disconnecting, unbolting, prying, etc. Once the new evaporator is installed it all goes back together in less than an hour.See where this is heading?
Everything is designed to be assembled quickly and easily. An assembly line worker has about 50 seconds to complete whatever task they have been assigned. They don’t have time to play around with trying to get something to go into place or line up bolts. It has to fit the first time, every time. There cannot be any wasted motion. Otherwise that task won’t get finished because the line keeps moving.
Service is also considered, but considered is the key word in there. It isn’t the main driver behind the process. Assembly is king. If the assembly plant can’t build the vehicle, who cares if service can’t work on it. It won’t be sold anyway!
Now of course, I, your humble blogger, was totally blameless in this (where is the emoticon that has it’s tongue firmly in cheek?). I never designed parts. I was always either in tuning or testing, never design. So blame anyone but me!
When taking things apart it can be very helpful to have the factory shop manual. The people that wrote this manual had access to the process sheets used in the assembly plant. These sheets tell how to assemble the parts into a vehicle. Knowing the exact order that it is assembled makes disassembly much easier. Sometimes fasteners are not accessible unless you take parts off in the proper order.
In my experience the non-factory manuals are worse than useless. They often have the wrong procedures, or at best, nothing at all! I read one of these where it was explaining how to remove the transmission. It said to remove the transmission! That’s all it said. I’ll be you already knew that part, but wanted some details. That manual didn’t have any details at all.