cudak888 

Before I do the proverbial parts throwing at this bike, I thought I'd see if anyone has seen this before:

I was testing a basically new Sturmey-Archer RXL-RD3 today when I lost gear selection entirely, finding myself stuck in first (not a fun ride back home). This surprised me a bit, for I figured it'd default to third given the return spring of the rotary unit.



I pulled the fulcrum lever, as Sturmey calls it - fairly confusing, given the chain-operated Sturmey fulcrum levers have a completely different purpose to this one - and found the spring in the rotary assembly had slipped. It's a straight offset torsion spring, and the inboard offset had slipped from its slot, allowing the rotating assembly to spin itself and the actuator into first - and stay there.

As designed, the tab of the spring is supposed to stay in place as follows:



So I reassembled the rotary fulcrum and tested it. It worked a few times...and then the spring snapped loose again at full tension.

That's when I gave the rotating unit a closer look. There are some witness marks and gouging from the spring slipping, and it is fairly obvious the spring under torque is probably compressing in width a bit, - but it hasn't been damaged enough that I would expect this difference of tolerance to result in the spring continually popping out of where it's supposed to be. This is, after all, a practically new part.



Any thoughts? Similar experiences? I have three other identical examples sitting here (and a fifth which appears to be slightly older production) and they do not do the same if the fulcrum actuator is tensioned fully (by hand).

-Kurt

GamblerGORD53

It looks like the hook is too long and or the groove is too shallow.
My first try would be grinding the hook end shorter and squarer.
I don't have one myself.

cudak888 

I see what you have in mind. My concern is that the spring needs all the width it can - cutting the tab shorter would allow it to pop out even easier.

I thought of the other way round (increasing the depth of the groove), but this would cause the spring to poke out and interfere with the rotary actuator on the hub.

-Kurt

oneclick 

Try making the hook a little more of an acute angle. The tension on the spring is clearly making the tab "cam" out of the hole - it'll only do that if it is not square to the hole, Set the tab enough further and under tension it'll only go to <90 degrees.

Of course, once the plate has suffered the hole itself may not be square, especially the part of the inner surface where the tab catches; you could try re-drilling the hole at a slight angle to fix that.

Moe Zhoost

Is it possible that there is too much slop between the two parts that sandwich the spring? If so, perhaps a shim under the c-clip might help.