Two ways: take a screwdriver and bang the spring in on the side that's pulling too far out. Or, conversely, pull the side that's not strong enough out and stretch it away from the caliper. Replace. It's an inexact science.
Im sort of confused, there's this long metal piece that goes under the arms, are those the springs?
because when i think of springs, i think of...springs on a car. They coil around and get higher and higher.
That is the spring - sits in the brake post stack, and comes out and does a loop before resting under a lip on each arm. You can use a screwdriver to press the end in and un-seat it from the lip. Then either push the spring end in on the strong side (essentially cold-setting it, to make it weaker) or pull out on the weak side (to make it stronger). Replace and test. Repeat as needed. I prefer the pull out, as I like a solid return.
Other things to consider with poor brake response: sticky cables (oil them), poor brake lever return spring, friction in the brake post stack (oil it).
i will take it all apart and play around with it.
What type of brake do i have?
single pivot U-brake, right?
And where exactly would i put oil for the cables to make them non sticky?
And how about the brake lever return spring? how would i fix that?
Basically, friction is the enemy of brake performance. You want to eliminate it anywhere it could happen. Drip oil into the housing where the cables enter. Also drip onto the stack of the brake post, where the brake arms rub.
Not sure if the return spring is fixable; it's probably not your problem. I'm assuming your problem is that one brake arm is lazy. If it turns out that you've adjusted the springs and oiled the cables and are still not satisfied with the lever return, then it may be the spring.
You don't need to take the whole brake apart to adjust the springs, although you certainly could. It's a little funny to get back together.
Whoa... Take a look at a few things prior to messing with the spring. The arms swing on a shaft that has nuts at both ends, and a 'dime' sized round block with a slot in it attached in the middle. The slot holds the spring.
In front of the spring is a double nut (cap and lock nut). Loosening these ever so slightly and lubricating will allow the two arms to move freely if they are binding. Also as per the above, check the cables for free movement.
The single nut on the other side of the frame cross brace has a plastic insert (acts like Locktite). This binds the assembly tight to the frame so that the calipers don't get pulled/pushed when braking. This also serves to lock the 'dime' into permanent position so that the spring tension left to right is held constant. If one side is not retracting as well as it should, try putting a wrench on the single nut and rotating the whole assembly slightly to put the spring slot parallel to the frame cross brace. I've seen them canted off so far, that one pad would never come off the rim.
If the spring really does have a bias, first try rotating the 'dime' slot past parallel, or resort to bending the spring. Try first releasing the spring from behind the two posts and see if it sticks out roughly an equivilent distance on both sides. Rotate the dime, or bend the spring to get it balanced.
Also remember that this spring centers the pads, and determines how hard you have to squeeze to work the brakes. If you pull the springs out far, be prepared to work harder. On my kids bike I pushed the spring way in - just enough spring action to retract the pads, and no more.