105 & Ultegra 10 speed shifter issue

[peetee]

I have discovered a issue with these shifters which may be of help to others who have suffered and know not why.
The indexing became very rubbery and imprecise, quite often missing a shift. On two occasions the cable snapped about 15mm from the barrel end.
The cause was found to be what I can only describe as a design fault and it is likely to happen repeatedly. The rotating barrel within the brake lever assembly which draws up the cable inner is not shrouded by the lever body. The barrel is ovalised and as the inner cable is drawn up the wide section swings round towards the exposed, inner face of the lever and catches on the rubber lever hood (pressed into place by the thumb in normal riding) and tiny rubber particles have covered the inner cable causing it to bind and drag where it enters the outer cable. As the indexing is released the inner has failed to follow the barrel and the slack cable has become kinked, frayed and eventually snapped.
While it would not be impossible for Shimano to have shrouded the shifter mechanism the resulting shape of the lever body would be noticeably bulkier and probably not suitable/comfortable for smaller hands. People's hand sizes vary as does the way they grip the bars so it is a problem that may well never occur for many people.
The photo shows the shaved hood in proximity to the mechanism.

[Brucey]

I wonder if a layer of (say) 0.25 to 0.5mm thickness polypropylene (PP) sheet between the hood and the lever body (secured to one or the other with double-sided tape perhaps) would improve matters?

With this in place, the lever workings would touch the PP, not the rubber, so little or no debris would be generated; also the sheeting would be flexible enough to defect out of the way when doing multiple downshifts etc.

BTW STI cables routinely fail at that location in all STI models, regardless of whether there is any rubber debris present or not. The reason for this is that gear cables have a very finite fatigue life when they are wrapped around a spool that size. One of my chums changes his cable inners every six months or so; I forget how many shifts he does exactly but IIRC his cables normally fail at about 130000 shifts (he changes gear a lot!).

Anyway the cable normally breaks a few strands and then starts to bind; once this happens it will kink if it can do. The kink isn't always in the same place as the first strands break, so this is a clue to the order of events.

cheers

[tim-b]

Hi
Thanks for sharing that. Which model of 10s lever is yours?
Regards
tim-b

[peetee]

I am fixing bikes regularly and the count so far is two 5700 105 rears and one Ultegra rear. both 10 speed.