I'm in the process of swapping the movement on my old Seiko 5 and I'm noticing some differences that I figured you guys might want to know about.
My plan was to just swap out the old broken 7S26B and replace it with the 7S26C from my newly upgraded SKX. I was going to swap in the calendar wheels from the old watch to preserve the stock color. This turned out to be impossible.
- The teeth on the date wheel line up differently with the numbers on the B vs C.
- The calendar retention plates are naturally different as well. Not only does the date spring line up differently, but the location of the alignment pins on the bottom calendar plate is also different. So this part cannot be exchanged either.
- The screw holes are in slightly different spots as well so the top plate won't swap either, not that I would need to.
- That teensy cross head screw that you need a special screwdriver for was mercifully redacted in the C revision. The plates are held down with 4 normal screws now.
- The other calendar parts (plastic correction wheels, 24-hour wheel, intermediate wheel, day disc) do seem to be interchangeable, for what that's worth.
- They added a bottom jewel for the mainspring barrel on the C version! I thought this only showed up on the 4R and 6R, but I guess they did it on the 7S as well. This of course means the barrel part is different. I've only ever been able to count 20 jewels in the old 7S26B despite my best efforts to find 21, so this may actually bring it up to the proper count. Maybe they got rid of one jewel from the A to the B version?
I went ahead and ordered a new black date wheel for the C movement, which is the same as the 4R/NH/6R date disc. I get the impression the purpose of the 7S26C revision was to standardize some of those parts across the range.
I may add pictures later if I get the mojo...