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Suntour XC self-energising / Pedersen-design cantilever brakes - how to disassemble ?
Anyone know how to take these things to bits ? Inside the cantilever
castings is a spring and some alloy "plugs" for want of a better word. The alloy "plug" is possibly a push-fit, and is threaded on the the inside - perhaps to aid removal ? Any ideas ? It's not the end of the world if I drill them out, but don't want to damage the springs, nor the arms, and it would be helpfull to not ruin the bits entirely so that I can reverse-engineer the design. By way of explanation, I've bought a couple of pairs of these off ebay. St John Street (Thorn) cycles have obviously got far too many so are knocking them out v. cheap if anyone's looking. These units have a clever feature that they are self-servoing from the rotation of the wheel. That is, as the wheel rotates, it pulls the unit against a spiral cam, which tightens them onto the rim even more. It may be debatable whether this is absolutely a good thing or not, and to be honest, having fitted the back one, I'm not sure it's really any better than the Avid Canti's I had before. However they are specifically made for the back only: on the front they would be anit-self-servoing, so no good at all! Apparently the equivalant on the front was too fierce and potentially dangerous. So bearing that in mind, I had the idea of making new parts to fit, but with the opposite "twist" so that they could be fitted on the front. I have good metalwork facilities (including lathe etc), but need to take the things to bits first. I dare say none of the above explanation makes any sense to anyone who doesn't have these - but then, unless you'd had a pair you wouldn't know how to strip them down. And even then I doubt if there's any reason to do so. Thanks Hywel |
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Suntour XC self-energising / Pedersen-design cantilever brakes- how to disassemble ?
hyweldavies wrote:
Anyone know how to take these things to bits ? Sorry, no, I haven't taken mine apart. The SJSC web site does suggest that it is possible to strip them down - try ringing them and asking? By way of explanation, I've bought a couple of pairs of these off ebay. St John Street (Thorn) cycles have obviously got far too many so are knocking them out v. cheap if anyone's looking. That's where I got mine. I also considered what would be involved in fitting them to the front. The conclusion I came to was the best way of doing it would be to find a set of forks with the canti studs on the rear. Such forks do exist, and others (like the Pace RC31) can easily be reconfigured to achieve this. One problem would be making sure you have enough clearance for the cable hanger. SJSC have their own solution to this issue he http://www.sjscycles.com/thorn/26tan...hurewebp11.htm Another problem, which may just be scaremongering but there is at least a theoretical issue here, is that you are introducing a positive feedback system to the front brake. The net effect of it taking over would be the involutary dismount over the handlebars. This would lead me to avoid mounting these brakes behind the fork, as there is still more positive feedback invoked if the forks twist as a result of the torque applied during breaking. Lots of toe in and front mounting would be the safest way to do it if it is worth doing at all. I think they are probably best suited to the rear, as the cable run is longer, therefore you would expect a larger amount of cable stretch on the rear. The self energising effect would tend to allow that longer cable to provide the same braking effect at a lower cable tension, thus making the rear brakes feel better at the lever than they would otherwise - even more so on a tandem, which is where SJSC tend to recommend them. If they don't feel better, its time to read up on cantilever geometry, as they are very tweakable. My link to Keith Bontragers article on canti adjustment has died, but thanks to the magic of google's cache, the good bit is this: quote The set up basics for any cantilever brake system: * Spread the arms at the top. Extend the pads out of the arms to do this. It seems weird, but it's important. Don't get carried away and extend them out so far that they are not held properly. Make sure they are held very tight when you are done with toe in adjustments. * Bring the straddle carrier down as low as you can. If you don't know how close you can get to the tire, adjust the lowest point of the straddle carrier even with the underside of the fork brace. This is a clearance you use all the time and is a good landmark to shoot for. * Adjust the pads first, then the carrier, them pull the straddle cable across and make the final cable adjustments. /quote Once all that has been done, you have cantilever brakes just as powerful as V brakes. I'm using them with Campag Ergo levers, and I get a reassuringly powerful rear brake effect (I have mini V brakes with Kool-Stop pads on the front). I'm not convinved the pads are the best available, but it won't get a set of Kool-Stop pads until they have worn out, and that may be some time as I agree with Sheldon Brown on use of the rear brake i.e. don't. So, my conclusion (which I now realise wasn't totally obvious from the rant above) was not to implement self energising brakes on the front, as I have got what I wanted out of the front brakes without the hassle of implementing a potentially dangerous solution to a problem best used on rear brakes. JimP |
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Suntour XC self-energising / Pedersen-design cantilever brakes - how to disassemble ?
Jim - thanks for comments. I'm sure you're right that it's not really
worth the trouble, and perhaps not even wise. I guess I'm doing it as a challenge more than anything. As a plan B I could convert them to non-self-energising which might be easier, and also suitable for the front. Hywel |
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Suntour XC self-energising / Pedersen-design cantilever brakes - how to disassemble ?
Jim - thanks for comments. I'm sure you're right that it's not really
worth the trouble, and perhaps not even wise. I guess I'm doing it as a challenge more than anything. As a plan B I could convert them to non-self-energising which might be easier, and also suitable for the front. Hywel |
#5
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Suntour XC self-energising / Pedersen-design cantilever brakes -how to disassemble ?
When I was a kid I modified my bike back brakes to be self-energising, and they were powerful but difficult to modulate, and when adjusted for even more servo action, wouldn't necessarily release. Soon I modified my back brakes back to standard, requiring more hand force but making them easier to deal with.
It would have been more difficult to do one for the front, and would have been scary and probably downright dangerous. Front brakes need to be finely controlled to keep our faces off the road under heavy braking. Personally, I would avoid self-servoing front brakes. You may land on your face. |
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