On Tuesday, December 11, 2018 at 5:54:45 PM UTC-5, Sir Ridesalot wrote:
Hi there.

I put Interupter levers on an MTB Drop bar bike with cantilever brakes and now drop bar levers feel spongy. The interrupter levers feel fine. Any ideas why the two different types of brake levers feel so different? I did NOT have this problem when I did the same thing to my touring bike also with cantilever brake calipers.

Thanks and cheers.

Hmm. I've got interrupters on two different drop bar bikes, and on
each bike all four levers feel solid.

Instead of pulling on the inner wire, the interrupters push on the
housing downstream - that is, the portion toward the caliper. They
don't move or change anything upstream to the original lever. So I
think the problem must have something to do with the installation
upstream, between the interrupters and the original levers. I'd look
for some sort of looseness or lost motion there.

Is the upstream cable housing and inner cable running as straight
as possible and pointed directly at the interrupters? Are the brake
cables "aero" (i.e. under the tape, like mine) or do they arc through
open air between the original levers and the interrupters? Seems to
me like crookedness or looseness in that cable run could be a suspect.

As an aside with a possible parallel: I firmed up the action of my
cantilevers considerably by pre-setting the bend in the straddle
cable of the brakes. My old-style straddle cables actually look
straight, like the one in Sheldon's copyright 1992 sketch at
https://www.sheldonbrown.com/cantilever-geometry.html
whereas lots of them have a bit of bend when the brakes are released.
That means lever travel first has to straighten the bend. (This isn't
as much an issue with more modern button-style straddle cables.)

Anyway, I wonder if you have some place where your original levers
are having to straighten out the cable. Obviously, it's hard to
diagnose this stuff remotely.

- Frank Krygowski