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Old 2016-08-18, 02:00 AM   #1
YooNeeNoob
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quick question 'bout the brake on my 36er...

I had a disk installed on my KH36 a year or two ago and have since grown to depend on it completely. It extends my range, makes impossible downhills possible, and generally improves my one-wheel experience. Since a disk on a unicycle represents a potentially devastating single point of failure, I've always been haunted by the fear of the 'nightmare scenario' in which I'm bombing down some steep slope, grab a handful of brake, and ...snap! ..something in the system gives out and I'm left with no brake force, like a cripple with his crutches kicked out. That's more or less what happened last Saturday for the first time. Thankfully, the hill wasn't all that steep, and I wasn't going very fast, but there's still a massive raspberry on my left knee that I could really do without (please, before you flame, yes, I know I 'm an irresponsible fool for not wearing ice hockey goalie gear everytime I ride, OK?).
So anyway, back to this brake: Like I said, it's been working great for at least a year, but I've lately been noticing some pretty advanced cable stretch--I was even going to take it in for adjustment, but apart from requiring a longer pull, the thing seemed to be performing well. I had just feathered the brake all the way down a 2-mile hill in fact, and was heading down another, much shorter slope when I felt an obvious 'pop' that felt exactly like the cable had in fact snapped; I instantly lost brake force and, naturally, tumbled to the ground, getting a good knee scrape in the process. OK, so the question(s):


1. the cable didn't break, so what actually happened?
2. did my neglect of the cable stretch condition contribute?
3. important: how do I avoid this sort of thing?
4. anybody else experience this?

THANKS!

Link to pic of brake:
https://goo.gl/photos/gLrmLoCbfcpFrzmP7

Last edited by YooNeeNoob; 2016-08-18 at 02:04 AM.
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Old 2016-08-18, 02:27 AM   #2
jtrops
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What kind of brake is it? Dual, or single piston?

While cables do stretch it isn't usually enough to change the brake performance. Most of the time loss of performance has to do with a mechanical problem, or brake pad wear. Depending on your caliper if you have enough space because of worn pads it may be enough to cause a pad to move out of position.

I worked on a BB7 a couple of weeks ago that had lost a pad, and the retaining pin had worn down to nothing on the rim.
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Old 2016-08-18, 09:17 AM   #3
Siddhartha Valmont
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(Injecting the pics).

I don't have experience with the TRP Spyke/Spyre but if the cable is not broken, maybe it slipped at the caliper side leaving you with a cable too long to move the pads. You can check the attachment on the caliper for any sign of slippage and tension the cable again just to see.

In your case, aside from the risk of injury because of the UPD, you have the chance of being able to do a repair on the train if the cable is faulty (by carrying a spare). In such scenario, it is far better than walk back to the car because it is too steep to be ridden without brake
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Old 2016-08-18, 02:06 PM   #4
waaalrus
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Quote:
Originally Posted by YooNeeNoob View Post
I had a disk installed on my KH36 a year or two ago and have since grown to depend on it completely. It extends my range, makes impossible downhills possible, and generally improves my one-wheel experience. Since a disk on a unicycle represents a potentially devastating single point of failure, I've always been haunted by the fear of the 'nightmare scenario' in which I'm bombing down some steep slope, grab a handful of brake, and ...snap! ..something in the system gives out and I'm left with no brake force, like a cripple with his crutches kicked out. That's more or less what happened last Saturday for the first time. Thankfully, the hill wasn't all that steep, and I wasn't going very fast, but there's still a massive raspberry on my left knee that I could really do without (please, before you flame, yes, I know I 'm an irresponsible fool for not wearing ice hockey goalie gear everytime I ride, OK?).
So anyway, back to this brake: Like I said, it's been working great for at least a year, but I've lately been noticing some pretty advanced cable stretch--I was even going to take it in for adjustment, but apart from requiring a longer pull, the thing seemed to be performing well. I had just feathered the brake all the way down a 2-mile hill in fact, and was heading down another, much shorter slope when I felt an obvious 'pop' that felt exactly like the cable had in fact snapped; I instantly lost brake force and, naturally, tumbled to the ground, getting a good knee scrape in the process. OK, so the question(s):


1. the cable didn't break, so what actually happened?
2. did my neglect of the cable stretch condition contribute?
3. important: how do I avoid this sort of thing?
4. anybody else experience this?

THANKS!

Link to pic of brake:
https://goo.gl/photos/gLrmLoCbfcpFrzmP7
I'm not an expert and I don't know a lot about the inner workings of the parts but I ride exclusively TRP Spyre/Spyke on both fixed and freewheels. I have a lot of wild UPDs which knock my brake out of alignment requiring a tweak. I've experienced what you're describing on my freewheel before and I think the problem was a combination of very worn brake pads and getting knocked out of alignment. Compared to your picture I have the arm of the caliper pulled in a little more in its resting state.
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Old 2016-08-18, 04:09 PM   #5
juggleaddict
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Just out of curiosity, what would you consider something impossible to ride down without a brake? It looks like you're running 150s, which should give you a lot of leverage for back-pedalling assuming your knees can take it. You could always go with a hydraulic rim brake. The Maguras are pretty bomb proof. A disc is probably great on a 36er though, where you really don't have many UPDs for typical riding.
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Old 2016-08-18, 06:25 PM   #6
Killian
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Quote:
Originally Posted by jtrops View Post
What kind of brake is it? Dual, or single piston?

While cables do stretch it isn't usually enough to change the brake performance. Most of the time loss of performance has to do with a mechanical problem, or brake pad wear. Depending on your caliper if you have enough space because of worn pads it may be enough to cause a pad to move out of position.

I worked on a BB7 a couple of weeks ago that had lost a pad, and the retaining pin had worn down to nothing on the rim.
Dual piston.

My suspicion would be cable slipping at the pinch bolt on the caliper.
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