Two questions about brakes
07-16-12, 01:21 PM
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Two questions about brakes
New cyclist here. I spent a bit of time this past weekend checking out my wheels and brakes (stock set of V-brakes on an '07 Fuji road bike), and I have two questions:
(1) Since the rear brake set was rubbing a bit, I spent some time adjusting the centering. However, I'm having difficulty because the entire V seems to have some lateral play. I can push or pull the arms into center, with equal range in both arms and both pads hitting the rims dead-center. But they don't seem very firmly affixed in that position - they can pretty easily get pulled to the left, such that the left pad contacts higher on the rim or even the tire and the right pad contacts lower on the rim, or vice versa. Of course, this also changes the tension on each arm and compromises the centering, to the extent that only one arm or the other moves during braking. I'm concerned that a jostle or even vibration on the trail could move them out of position and even cause the brakes to fail.
Initially, I thought that this was a problem with a loose bolt somewhere - maybe at the top of the V or elsewhere - that would hold the brakes in alignment if tightened. However, I can't seem to find anything to serve this function, and in fact the sources of information I've read don't even mention anything about this problem, so I'm concerned that the brake is actually borked.
Any ideas?
(2) After playing with both brakes a bit, I've noticed two minor changes in the brake cable. Wondering if you can help me restore either or both to normal.
First: The rear brake cable seems more sticky now - it doesn't always spring back to a fully disengaged position. I can't really find any reason why it's behaving like this - there's no pressure or kink in the cable - and it definitely didn't get dirty. I thought briefly about WD40ing it, but remembered that this is wrong because it can interfere with the Teflon lining of the brake line. Ideas?
Second: The brake cable ends with a quick-release mechanism, with small metal plug that fits into a bracket. Before my poking and prodding, this mechanism was covered by a small rubber sheath that seemed to fit tightly around the plug, but that could be retracted. However, now the sheath seems loose - it won't stay over the mechanism. Also, the other end is beveled (like the bend in a straw) so that it should collapse into itself when squeezed by the engaged brake, but now the brake causes it to bend instead.
It feels almost like the opening that covers the mechanism was tight but is now stretched out, although I swear I didn't tug on it. Why is this happening, and what should I do about it?
Thanks again, everyone.
(1) Since the rear brake set was rubbing a bit, I spent some time adjusting the centering. However, I'm having difficulty because the entire V seems to have some lateral play. I can push or pull the arms into center, with equal range in both arms and both pads hitting the rims dead-center. But they don't seem very firmly affixed in that position - they can pretty easily get pulled to the left, such that the left pad contacts higher on the rim or even the tire and the right pad contacts lower on the rim, or vice versa. Of course, this also changes the tension on each arm and compromises the centering, to the extent that only one arm or the other moves during braking. I'm concerned that a jostle or even vibration on the trail could move them out of position and even cause the brakes to fail.
Initially, I thought that this was a problem with a loose bolt somewhere - maybe at the top of the V or elsewhere - that would hold the brakes in alignment if tightened. However, I can't seem to find anything to serve this function, and in fact the sources of information I've read don't even mention anything about this problem, so I'm concerned that the brake is actually borked.
Any ideas?
(2) After playing with both brakes a bit, I've noticed two minor changes in the brake cable. Wondering if you can help me restore either or both to normal.
First: The rear brake cable seems more sticky now - it doesn't always spring back to a fully disengaged position. I can't really find any reason why it's behaving like this - there's no pressure or kink in the cable - and it definitely didn't get dirty. I thought briefly about WD40ing it, but remembered that this is wrong because it can interfere with the Teflon lining of the brake line. Ideas?
Second: The brake cable ends with a quick-release mechanism, with small metal plug that fits into a bracket. Before my poking and prodding, this mechanism was covered by a small rubber sheath that seemed to fit tightly around the plug, but that could be retracted. However, now the sheath seems loose - it won't stay over the mechanism. Also, the other end is beveled (like the bend in a straw) so that it should collapse into itself when squeezed by the engaged brake, but now the brake causes it to bend instead.
It feels almost like the opening that covers the mechanism was tight but is now stretched out, although I swear I didn't tug on it. Why is this happening, and what should I do about it?
Thanks again, everyone.
Last edited by sfsdfd; 07-16-12 at 03:25 PM.
07-16-12, 07:35 PM
#2
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1. the brake-centering is done by screwing in/out a spring-preload screw.
https://www.parktool.com/uploads/imag..._centering.jpg
Follow this Park Tool - V-brake service guide
2. the part you're referring to is often called the "noodle". Post a photo of your set-up. The brake-cable housing may not be seated properly.
https://www.parktool.com/uploads/imag..._centering.jpg
Follow this Park Tool - V-brake service guide
2. the part you're referring to is often called the "noodle". Post a photo of your set-up. The brake-cable housing may not be seated properly.
07-18-12, 04:21 AM
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Road bikes rarely come with V-brakes. There's Mini-Vs, but even those are mainly found in the realm of cyclocross bikes and maybe the occasional tourer. Are you sure you've gotten your words right?
But the part about "beveled rubber sheath" does sound like the seal on the end of a V-brake noodle.
Then there's that part about "a bolt at the top of the V". The only thing on a V-brake corresponding to that which I can think of is the cable clamp, which has a fairly simple task to perform. If insufficiently tightened, cable will slip. If overtightened threads will strip.
Lubing cables is a so-so idea. While it may help initially, it can also encourage gunk build up and cables sticking further ahead.
Then there's that bit about "pads contacting higher up the rim". The brake pad will swing through its arc, determined by the pivot point and placement of the pad regardless if you actuate one , or both halves of the brake. Apart from the pad itself moving, the only way to get a different contact point on the rim would be through moving the rim sideways too.
Unless you're mistaken about brake type, and actually have a dual-pivot caliper brake, as suggested by the spec on the Fuji bikes website. Or a centerpull caliper brake for that matter.
For info, try here, and associated links.
And centering is rarely a critical feature. Brakes work by pinching the rim between the pads, so performance-wise you should be OK. You'd want the pads to clear the rim when disengaged though, as touching will eventually wear down the pad for no purpose.
But the part about "beveled rubber sheath" does sound like the seal on the end of a V-brake noodle.
Then there's that part about "a bolt at the top of the V". The only thing on a V-brake corresponding to that which I can think of is the cable clamp, which has a fairly simple task to perform. If insufficiently tightened, cable will slip. If overtightened threads will strip.
Lubing cables is a so-so idea. While it may help initially, it can also encourage gunk build up and cables sticking further ahead.
Then there's that bit about "pads contacting higher up the rim". The brake pad will swing through its arc, determined by the pivot point and placement of the pad regardless if you actuate one , or both halves of the brake. Apart from the pad itself moving, the only way to get a different contact point on the rim would be through moving the rim sideways too.
Unless you're mistaken about brake type, and actually have a dual-pivot caliper brake, as suggested by the spec on the Fuji bikes website. Or a centerpull caliper brake for that matter.
For info, try here, and associated links.
And centering is rarely a critical feature. Brakes work by pinching the rim between the pads, so performance-wise you should be OK. You'd want the pads to clear the rim when disengaged though, as touching will eventually wear down the pad for no purpose.
07-18-12, 08:57 AM
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Never mind about them sitting on one side or the other when you give them a poke. It's how they sit when you let go of the brake lever that matters; this is where they'll vibrate to when you're riding too.
Also I'm pretty sure PTFE has no problem with oils, or they wouldn't coat frypans with it.
Also I'm pretty sure PTFE has no problem with oils, or they wouldn't coat frypans with it.
