Weird rear V-brake issue

[Larry H]

Can't seem to find this in any existing thread. I have the brakes properly centered and not rubbing on the wheel at all, when at rest.

The problem I have is most noticeable when applying the brake slowly; what happens is that the right arm (the one to which the cable is bolted) is the only one to move through the first part of my hand lever's travel. As the hand lever is pulled with increasing force, the right pad just makes contact with the rim and then stops moving. At this point, the left (stirrup) arm begins to move, and with yet more force from the lever, only the left arm then moves until it too touches the rim.

My front brakes don't do this; the motion of both arms is smooth and even all throughout the travel of the hand lever.

I can't figure out what is causing this problem with the rear. The fact that one pad is grabbing before the other would seem to be a great way to knock the wheel out of true; the right pad is essentially pushing the whole wheel into the left pad when I apply the rear brakes.

I'm beginning to think this could be a cable housing issue, but I don't know for sure. Any ideas?

[cyclerUK]

Check out this previous thread:-
http://forums.bikeride.com/thread-1957.html

Try adjusting the "centering screws" as shown on the diagram.
Screw in the screw of the arm that moves first and screw out on the arm that moves last.
Also check that the arms move freely by unclipping the noodle. Both arms should move freely with equal tension.
The spring for each arm is located in a hole on the frame. Check that they are both in respective similar holes.

[trevgbb]

If everything is set up OK as cycleruk post then possibly due to corrosion on the bearing surfaces of the pivot arms.
Remove the brake arms, noting the assembly sequence, and clean up the pivots using fine emery, regrease and reinstall, making sure that the adjustment screw is properly aligned with the end of the spring as this sometimes slips past and overrides the spring.

[Larry H]

Thanks for the help, trevgbb and cycler.

What I ended up doing was a little more than your suggestions, but I think the problem is taken care of. I completely dismantled the whole system -- that is, unbolting the cable, then unbolting the arms from the brake bosses -- and once that was done and the brake arms were off the bike, I turned the centering adjustment screws as far out as they would go.

I then proceeded to bolt the arms back onto the bosses, with no tension at all on the springs. This was followed by a readjustment of the pad positions on each side; I think that's easier to do with zero spring tension wanting to push the arms back away. Once the pads were set to my liking, I turned the adjustment screws clockwise far enough to force the pads off the rim, using my eyes to judge when they were evenly far from the rim, and then reconnected the cable.

Until cycler's message, I was unaware that there are actually two functions those screws serve. Most people assume they're just for centering the pads properly, i.e., correcting a side-to-side imbalance of the resting pad positions; but they also control the amount of spring tension trying to force the pads back to rest.

It is quite possible to have the situation I had: the pads are an equal distance from the rim on both sides, but one arm has substantially more spring tension to overcome than the other, and the arms will thus move unevenly.