I know what you mean regarding repair books from the 70s. When my kids wanted to know how to do something on their bikes, I'd send them upstairs to our library to read about it before I would help them. They always complained that the books were too "old". Being somewhat dutiful kids they would go read about the particular procedure, and I would then help them. One day, looking for a gear chart, I picked one of the books up again. It was amazing to me how much had changed and how little I realized it because of making incremental adjustments in my knowledge and work over the decades. Figuring out something like changing a cable on a grip shifter could indeed be perplexing.