S5 Sun gear issue.

[FICHT 150]

I’ve owned perhaps a dozen of these hubs over the years, and while the adjustment can be a bit finicky, they have been serviceable and reliable hubs for me over the decades. I had one that had a slip in ultra low gear, and I could never chase the slip away. A slip in this gear is disconcerting, to say the least, while trying to muscle up a certain hill we are familiar with. The factory instructions gave a few culprits to check, I dutifully pursued them all and really got nowhere.

Turns out the factory forgot one.

Notice the two sun gears in the photo posted. The sun for an S5 usually has small ramps cut in the top of the lugs, to speed engagement with the corresponding gear, for lack of a better term, on the axle. This particular sun was machined with the entire lug as a ramp, which, is going to make it damn hard for it to be solidly engaged with the axle.
The other sun gear is the slightly different part number that is used in an S5/2 hub, and, perhaps, others. I knew it was in a homeless hub I had on hand. If there are folk that seek out and run S5/2 hubs, I’ve yet to meet them.
My guess is they quit machining the ramps to save a step in the process, but, who knows? I removed the offending part, and installed the newly harvested S5/2 sun gear. There is no question that it will solidly engage the axle. It might take a fraction of a second longer to do that, but, I don’t see that being an issue.
Full disclosure, the last AW hub I converted to S5 specs, (you need a homeless FW hub to do that) used an identical sun gear that turned up in my parts pile. So, I knew it worked, but, I’d never seen a sun gear that was so clearly defective as the one that came out of this S5 hub. I imagine some kid had a frustrating bike that never worked right.
Ted

 

[SirMike1983]

Yes, it's better just to swap one of those parts than to fool with it, re-assemble and test it. The disassembly and re-assembly is slower than on an AW. You might as well just put a known good part in and go. The S5/2 flies under the radar. They're decent hubs but being from a later era, they don't get quite as much interest as the early S5.

Sturmey would make gradual changes to hubs, but the changes are not necessarily well-documented (at least for the public - perhaps some hidden old Sturmey Archer archive would show it). I recently rebuilt two FW hubs, one from the late 1940s and one from the late 1950s. Despite often being referred to as the same hub, the 1940s hub had a few parts the 1950s hub did not have. I would guess cost savings were the reason why. The parts helped take a little play out of the planet gears but were not a big deal. The 1950s hub works just as well as the earlier one. But you'd never know those difference were there unless you opened the hubs up and compared.

 

[FICHT 150]

I am told one can use a diamond file to “convert” the ramps on the sun gear used in a FW to be square at the base, and be a passable S5 sun gear. But, I’m lazier than that, and since I live just up the road from the Bikesmith, and his parts hoard, I just buy an S5 sun from him, or, make mental note of where to turn one up, an S5/2 sun being an excellent replacement.
I owned S5 bikes for most of a decade before ever having an AW equipped bike, and learned how to rebuild S5 hubs years before I ever had an AW apart. I’ve got more time than money, but, it doesn’t really take much more time for me to do an S5 than an AW, an AM, or, an FW. I’ve converted a few AW hubs to S5, the last one is my DL-1 Roadster that is happily much improved with the two additional gears.
Sitting on my bench is an FM in an alloy shell, with the delicate looking indicator rods, and an NOS 4 speed shifter. I’m probably going to build a bike just to try the thing.
I’m easily amused.

Ted