Shudder / vibration

Took kids for rides around the neighborhood last night. A few times the bike had a vibration as the foot brake was applied. Is this one of the signs of the pads needing replaced? Any other things I should be checking?

 

Could be, eassy enough to inspect.
Also check that the rotor is running true by spinning the wheel, and that the caliper is releasing.

 

Check that the disks are clean. I got some tire bead lubricant on my front disks and had to clean them with alcohol. Maybe some grease or chain lube got on the disk.

 

Any tips or good How-to write-ups on checking and changing the brakes. Or is the manual the best bet?