Can anyone run me through the steps to replace the RD cages on a 70s NR. I'm ordering a set of longer cages from eBay. As far as I can tell, I remove the lower pivot bolt and that releases the cages. Also there is something mentioned about a holding screw and spring?

Thanks in advance

Take the tension off the grub screw, that cylindrical chromed post with the screw slot in it that provides the stop for the cages unwinding. It is scewed into the chromed barrel of the lower pivot body. Notice how many turns of tension on the lower pivot spring as you slowly let it unwind. Once all the tension is off the spring, which is inside the lower pivot body, you can take a hex wrench and remove the lower pivot bolt. Note that there are two holes in the inner cage, which the end of the spring goes into, to hold the spring in place. Clean up everything inside, re-grease the spring and re-assemble with new cages. Make sure you get the end of the spring in one of the holes and it is oriented properly inside the lower pivot body. Wind up the spring by rotating the cages CLOCKWISE when looking at the REAR of the derailleur. As I remember, one turn will do it. Hold the cages and derailleur in one hand, keeping tension on the spring, while inserting the grub screw back into its place.
Kind of easier to do than explain.

Try googling stuff like this; great BF thread with an exploded diagram:

https://www.bikeforums.net/bicycle-me...-question.html