TSDZ2 Large Sprag Clutch: What Causes Wear?

[PeteCress]

Not the clutch in the blue gear, but the larger one.

Is it worn more, the more hours that the motor is assisting?

Vice-versa?

Is the failure mode sudden/total or gradual?

Mainly, can failure strand the rider by rendering the bike not pedal-able even without motor assist?

Finally, can anybody suggest a pre-emptive replacement interval?

 

[jeffieh]

You'll know when your sprag clutch fails - your pedalling won't engage with the chainring, & the cranks will spin freely. From personal experience this can happen gradually, with occasional slippage that seems to get worse with time. My bike (approx 12,000km from new) had been doing it from about 7000km. First action was to strip it down and clean the clutch out (be careful - it's super easy to lose pawls & springs!) and this bought me another 4-5000km without too much drama. However it got steadily worse in recent weeks (slipping way to frequently for my liking) so I took everything apart again and fitted a new, higher quality sprag clutch. It's doable without specialist tools, just some allen keys, circlip pliers, and possibly a hammer and punch (some light taps on the outer race if the bearing refuses to shift). No slipping now, and as a bonus the motor feels smooth-like-new.
As for stranding you, I don't think that's likely, because not all of the pawls would fail at once.
Hope this helps.

 

[jeffieh]

Ha, I see you posted this back in May! Hope you haven't been waiting all this time for an answer