I feel vibration or throbbing when I brake?

Here are some points to consider if your braking is uneven.
1. Ascertain if the vibration is due to impact damage. This is easy to assess, just run your hands around the brake track. It should feel even width and uniform finish. If damaged, other measures are required; usually replacing the rim is your best option.

2.Cleaning the rim can be done with solvent. Lacquer thinner (keep away from the tire) and alcohol are effective. Don’t leave any residue of pad material on the brake track. Melted pad material will accumulate in spots and, eventually, the accumulation is the enemy. The imperfection that started the accumulation might be fairly undetectable. But the melted off brake pad material creates terrible changes in friction and, consequently, brake vibration.

3.Some like to remove their tires and lightly sand brake tracks, especially after nasty, gritty, wet riding, where the track is scarred (but the rim’s width is still uniform). Use 80-120 grit and only light pressure. You’re not trying to make the surface smooth, per se, just more uniform.

4. Brake pads can develop a glaze on their contact surface and inhale bits of grit and rim material. Sanding them can help restore their friction. Remove the wheel so you have easy access to the pads.

5. Some forks are so light that they don’t do a good job of dampening shock or vibration. No solution here. Few of today’s forks excel at dampening. The stronger, heavier ones (built for harder use) automatically and unintentionally have better dampening. Lack of dampening means the fork is content to move back and forth without absorbing energy and slowing the movement down.