dabac

Hi all,
I got hold of a bike with an early version of Nexus-7 w/ coaster brake. It came with AR washer only on the drive side.
I can’t tell if one has gone missing over the years, or if it came like that.
Does a coaster brake nexus need two AR washers, or will the brake arm suffice to hold that end of the axle in place?

Dan Burkhart 

I'm not sure about the earliest version of the Nexus 7, but any I have dealt with had axle flats on both sides and anti rotation washers both sides.
The coaster brake reaction arm only serves to hold the brake plate in place. It does nothing to keep the axle from rotating.
If the left side has no flats, then there would be no way to mount a washer. The 3 speed Nexus uses only one washer on the non drive side.

dabac

Until now, the same here. Both sides have flats, only one has the AR washer. The NDS though has A washer, same thickness as an AR washer, but no tab. So it looks original.
Dang. Might have to dig into my stash then.
So what might have happened here, has someone shifted the washers around? Or lost one? Or both?

EDIT:
My bad. I went and had another look. The NDS doesn’t have any axle flats.
So if anyone should encounter a coaster brake Shimano sg-7c22 from about 1999, it only has one AR washer, and it goes on the drive side.
The ”socket” at the hub where the shifter cable hooks up is wider than on more recent Nexus hubs.
Don’t know if it originally came with a slightly different style clamp-on button. The current buttons can be attached and work, but are a somewhat worryingly loose fit.
They more or less fall in/out of engagement once the tension is off, as opposed to the wiggle-and-curse mode of connect/disconnect on the more current versions.

dabac

I’ve had a think about that. Outside the reaction arm, there’s a nut/locknut set. The purpose can’t be anything else than keeping the brake arm in place. If you lock the brake arm in, you are keeping the axle from rotating. If it didn’t, the brake would become self-energizing.
And 3-speeds obviously do OK w/o the NDS AR washer.
I haven’t checked the ratios.
But unless the 7-speed has a significant lower 1st gear compared to the 3-speed, I can’t see why a 7-speed w/ coaster brake would need a NDS AR washer anymore than a 3-speed.
Maybe the NDS AR washer is added primarily to keep the build consistent between the Coaster/roller brake versions and the unbraked versions?

Dan Burkhart 

I did have a vague memory that the first generation Nexus 7 did indeed have axle flats on the drive side only, thanks for confirming that.
There were some IGHs that had no anti rotation washers at all, namely Sachs Orbit (which I just had my hands on as recently as a week ago,) and the Sachs dual drive. They relied on an aggressively serrated lock nut to keep the axle from rotating.
Yes, the lock nut does inhibit the brake plate from rotating in relation to the axle, but it does not positively prevent it. If you need proof of that, disconnect the arm from the tab on the chainstay and you can rotate the arm if you apply enough force.