Shimano cantilever BR-M732 asymmetry

[Nicholas Grieco]

Last weekend, I installed Shimano cantilever brake BR-M732, which is
sometimes called 'XT2', or 'XT-II" as I understand it.

I found that the arm with secondary spring tension adjustment has more drag
at the pivot than the other arm. This causes the two arms to respond
asymmetrically when the brake cable is pulled or released.

The drag appears to be integral to that cantilever arm; different greases
and lubes on the brake bosses did not correct for the differential.
Loosening or tightening the pivot bolt had no affect. Unequal left/right
spring tension and/or straddle cable length do not directly address this
problem.

With some Googling, I found a post referring to this issue:
http://tinyurl.com/6273n, or
http://groups.google.co.uk/groups?hl=en&lr=&[email protected].
edu

Has anybody else here experienced this? Did Shimano make a running change
to the 732 to correct the issue? Does the 730 have the same problem?

Thanks,
Nicholas

 

[Sheldon Brown]

Nicholas Grieco wrote:

> Last weekend, I installed Shimano cantilever brake BR-M732, which is
> sometimes called 'XT2', or 'XT-II" as I understand it.
>
> I found that the arm with secondary spring tension adjustment has more drag
> at the pivot than the other arm. This causes the two arms to respond
> asymmetrically when the brake cable is pulled or released.
>
> The drag appears to be integral to that cantilever arm; different greases
> and lubes on the brake bosses did not correct for the differential.
> Loosening or tightening the pivot bolt had no affect. Unequal left/right
> spring tension and/or straddle cable length do not directly address this
> problem.

> Has anybody else here experienced this? Did Shimano make a running change
> to the 732 to correct the issue? Does the 730 have the same problem?

This is not likely a flaw in the cantis, more likely a flaw in the frame
studs. Sometimes they can get bulged out near the open end from
overtightening of the bolts, sometimes they're imperfect in other ways.
This can often be corrected by careful use of emery paper or a file.

Also, those cantis have a two-position spring setting (on each side.)

One of the positions is labeled "SLR." This is the lower-tension
setting, for use with brake levers that incorporate their own return
springs.

The other, stiffer setting is for older brake levers that relied on the
canti springs alone.

I have a detailed series of Web pages on this, but now that I look, it
appears that I neglected to place a link to them anywhere on my site.

See:
http://sheldonbrown.com/harris/cantilevers/pages/cantilevers-xt2-02.html

Sheldon "Oopps!" Brown
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