Fixing a Too-small Derailleur Cable Ferrule

Brass tubing to enlarge ferrule
Brass tubing to enlarge ferrule

While replacing the rear derailleur on Mary’s Tour Easy, I rediscovered that I have two different cable sizes in my stash: large brake cables and small derailleur cables.

The large ferrules are 0.235 inches in diameter, the smaller 0.187 inches. The brazed-on cable-stop sockets are obviously sized for the larger ferrules, which makes perfect sense.

If you put a small ferrule in a large stop, it tends to cant whichever way the cable pulls it. That results in the cable sawing into the edge of the ferrule… and that results in excess friction and sometimes a broken cable.

In the past I’ve snipped out little brass shimstock rectangles, wrapped them around mandrels, and generally spent a lot of time fiddling around. This time I remembered to rummage in my collection of brass tubing cutoffs, which yielded a pair of very-nearly-perfect slip fit pieces that neatly adapted the small ferrules to the large stops.

Rear shift cable with modified ferrules
Rear shift cable with modified ferrules

Life is good…

I have no idea what the cables look like on weight-weenie exotic-frame bikes. For sure, this isn’t a trick for hydraulic disk brakes.

Incidentally, the cable housing length worked out to 130 mm. Neither of the charts in the SRAM X.7 instructions matched the TE’s butt end; the seat stay angle is halfway between what’s normal for diamond-frame bikes. So we picked a reasonable length and it seems to be OK.