Take the 2-minute tour ×
Bicycles Stack Exchange is a question and answer site for people who build and repair bicycles, people who train cycling, or commute on bicycles. It's 100% free, no registration required.

I'm not a big expert, so forgive me if I use some terms wrong (especially because I'm not a native English speaker).

I have a MTB with V-brakes. I wanted to tune the rear brake because it looked like the pad were working asymmetrically (with the right pad being closer to the wheel). What I noticed, though, is that the whole brake tends to "move" to the left, where the noodle is. If I pull the whole brake to the right with my hand then pull the lever, the right arm gets pulled while the left one stays almost in place; when I release the lever, the right arm stays in place and the left one gets away from the rim. After that, pulling and releasing the lever seems to affect only the left arm - with the right pad staying quite close to the rim, to the point that the wheel is always braking.

In short, if I understand it correctly, the brake arms should look like a V ( \ / ) and become parallel when pulled ( | | ); instead mine look like this ( \ | ) when released.

The bike has fourteen years and a couple of accidents on its shoulders (one affected the rear wheel, but I had it repaired at a shop, and AFAIK the rear brake was unaffected). Is this problem due to bad tuning? How could I fix it? Or should I forget about it and get a new brake?

Thanks!

share|improve this question
1  
There are springs in the pivots that, for most brakes, are adjustable. It's not uncommon to need to adjust the spring on one side to achieve "balance" between the two sides, even on truly symmetrical center-pull cantis. –  Daniel R Hicks Nov 5 '13 at 11:55
    
Thanks Daniel, I'll check more closely on that too, but it seems to me that there is no spring in the arms, just the screw in the bottom - which is very very tight for both arms. The only adjustable parts I can see are the pads and the cable stop in the right arm. There's also a screw in the stirrup, but I have no idea whether that tunes anything. –  Simone Nov 5 '13 at 12:00
    
The small screws (not the ones that the arm pivots on, but near the pivots and at right angles to them) should not be "very tight", but should stick out, showing several threads. –  Daniel R Hicks Nov 5 '13 at 12:27
    
Do you mean the small screws that stick out in this picture? i00.i.aliimg.com/wsphoto/v0/450220768/… I was in fact talking about the pivots, when I mentioned them being very tight. If I understand correctly, the spring action should come from the pivots themselves, and the small screws will tune how hard that spring is? –  Simone Nov 5 '13 at 13:40
    
Yes, the small screws adjust the spring tension. But of course first make sure that the arms are moving freely. –  Daniel R Hicks Nov 5 '13 at 16:06
add comment

1 Answer

Please do the following experiments:

Release the brake cable, pulling (1) apart from (2) (no tools needed). Swing the brake arms one at a time, making sure they have nice spring-y reaction the last 2-4 centimeters of their travel towards the rim.

  • If the movement feels "rusty" and the swingarms don't readily return, there is mud and rust inside the breaks. Replace them.

enter image description here

Now check if both push back with the approximately equal force, when at equal distances from the rim.

  • If one arm pushes back significantly more than the other, the coarse setting is wrong.

With the brake cable still disengaged, squeeze the brake lever a few times.

  • If there is any resistance, or if the cable looks rusty, it should be oiled/replaced.

When the brake arms are pressed against the rim, the brake shoe should rest fully against the rim (in contrast with only half the pad touching the rim or touching the tire). If this is not correct, the brake shoe can "latch" when pressed, sticking to the rim by friction.

Most probably the brakes and cables are rally old. You can disassemble those parts, wash them under pressure, let them dry and re-install them, or you can replace them with more modern parts.

share|improve this answer
    
Thanks for the detailed answer! I'll be sure to try it when I get home. –  Simone Nov 5 '13 at 11:56
    
@Simone, my answer is valid in case Daniel's comment fails to fix your problem. The adjustment screws for the spring are usually small and located to the side. Tightening them increases the spring tension, moving the V-arm further away from the rim. –  Vorac Nov 5 '13 at 12:05
    
if there is rust, you can lubricate it with oil. Not always you have to replace them (especially on cheap bikes). –  Alexander Nov 5 '13 at 21:33
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.