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Requesting some Diacompe/SunTour XCM cantilever brake help

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Requesting some Diacompe/SunTour XCM cantilever brake help

Old 07-06-19, 04:55 PM
  #1  
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Requesting some Diacompe/SunTour XCM cantilever brake help

I've used these brakes(as well as XCT and XCE) on a few different bikes, but setting the XCMs up on an early 90s Cannondale T700 is not going well.
Wondering if they aren't compatible(thatd be a first for me).

These brakes use the fitted washer(lack of proper term) to friction press up against the brake boss on the frame which improves micro-adjusting instead of relying on the typical 3 holes on the frame.

The fitted washer doesn't sit flush against the brake boss. I tried both the DS and NDS sides out of curiosity. Same issue on front and rear brakes.
See pics below. There is a visible gap that won't go away and that is as close to the frame as the washer gets.



So-
- is there a trick to using these with some frames?
- is this frame different from others?
- is this an issue with some frames and I just haven't come across it or read about it?
- am I missing something obvious?

I have 2 sets of these, so I would rather not buy more cantilever brakes, but will do that if needed.


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Old 07-07-19, 01:28 PM
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Bump, in case someone today happens to have an answer.
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Old 07-07-19, 02:16 PM
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I don’t have a definitive answer although I suspect that there is some trick to this that we haven’t yet discovered. I have a similar issue with SunTour “XC” cantilevers that I was attempting to use on my Trek Multitrack that I am re-building. The Canti caliper on the right isn’t like this, only the one on the left (IIRC). The one on the left has a nut on the backside that I believe is to be used to tension the spring against the Allen head post bolt.

Like you, I thought there was an incompatibility where the cantilever stud appear to be too long. The cantilever studs on my frame are the non-removable type so I’m not inclined to experiment and take a grinder to the end of the stud to shorten it. If the studs were removable, I might sacrifice a couple of studs and take some length off the end on a bench grinder.

My second thought was that there might be some missing washers that, if I had them they could space the caliper out enough so that the caliper can be tightened sufficiently to permit spring tensioning to match the opposing caliper arm.

SunTour parts BITD were often like this I have found. Very logically designed if you have the instruction sheet and the correct wrenches. I have functional wrenches for the job but have not solved this yet.

I hope folks can help here and that you are able to get the brakes mounted. I will be following this thread....
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Old 01-15-20, 07:04 PM
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Bump: to mstateglfr

Just curious to see if you came up with a solution to this issue?
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Old 01-15-20, 10:09 PM
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Try looking into the setup of Suntour Rollercam brakes. Those should be well documented and are likely similar.

if possible post a pic of all your caliper parts. I think on some of these the hardware on one side is different than the other.
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Old 01-15-20, 10:32 PM
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Originally Posted by Chuckk
I just puzzled out the problem with XC cantilevers on my SH800 - they just didn't work right and I was baffled by adjustment.
On those cantilevers, there's a brass bushing that runs between the brakes and the pivot shaft.
It's a little longer than the pivot length of the brake, and on mine they were either stuck to the pivot or the cantilever.
Pop them out or pull them off, clean up all the surfaces and add a touch of grease.
Then, when you tighten up the pivot bolt, it tightens to the base through the long bushing and you adjust the spring tension by rotating the base part while snugging it up.
My base parts had a thin hex on them, yours have a pair of flats? I didn't have a skinny enough wrench, so held them away from the wheel as far as I needed to get proper spring tension.
I've had a similar issue in the past and the advice here that Chuckk is giving seemed to work for me as well. Like the brass pieces needed a gentle scrub and then lube all the moving bits and then it seemed to work again. Not the best design.
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Old 01-16-20, 06:17 PM
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I've got a few bikes with XC Pro cantis on- sort of the same concept.

Just looking at them- they're seated against the base of the canti stud- HOWEVER- I don't think it's going to matter too much if they're not against the base- as long as that center cylinder is locked down and won't move- you're golden, so to speak. The brake arm rotates around that cylinder-

The screw holds the cylinder on, the tension is on the collar with the 13mm wrench.

Shoot me a PM if you're still having trouble.
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Old 01-16-20, 10:34 PM
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Originally Posted by masi61
Bump: to mstateglfr

Just curious to see if you came up with a solution to this issue?
I ended up using some shimano cantis and they worked perfectly. I tried xcd, xcm, and xce cantis on this frame and none worked for the same reason.

The xcd ones are what's on my old gravel bike that you asked about in another thread.

This cannondale was the first time I've come upon canti posts that didnt fit whatever brakes I wanted to use.
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Old 01-17-20, 05:49 AM
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Not sure if it's relevant but there was a good guide to preparing brake posts for canti brakes in the last but one BQ, it may be that something isn't quite finished off right on the brake post.
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Old 10-30-22, 06:06 PM
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zombie revival thread! (i'm the zombie revival master....)

Some details on the Dia Compe XCM 5583
The do-hicky with the flats (DHwF) is to adjust torsion spring tension (RJ Bike Guy video link at the very end). Use a 13mm cone wrench to adjust the tension.
The DHwF goes over the fat part of the canti-post, and as previously mentioned, the steel sleeve is clamped with the mounting bolt. The brass bushing between the steel sleeve and the brake arm rotates.

Some detailed pics below:
As installed - note the direction of the plastic bit, it open end is toward the frame, not the canti-arm:


Today, here's where I got all confused and found this post. And the RJ video:
If you just go and try to not use the DHwF, then you think the torsion spring goes into the post - no, the canti arm spring direction is all bass-ackwards.



The DHwF goes OVER the post (it's like got a big inside diameter, and an ID that matches the post outside diameter)

The flats allow you (or me...) to adjust the torsional spring tension.

Here's a pic where I got the plastic bit backwards - I didn't realize until I started typing this up - I could NOT figure out why the DHwF and the plastic bit would not nest. I got it backwards here:


OK - I think that's it. Hopefully this helps someone in the future - all these added details. Hopefully. - and make sure you get the plastic bits on the right way - i gotta go fix that...... tomorrow.


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