Are you working on your brakes on your Suzuki DR-Z400? Check the state of your brake pad pins. They tend to seize as they are made of relatively soft steel.
 
You can often find them quite corroded and even bent (especially on the rear calliper). If the pin's shaft is corroded, you might strip the head when removing it.
 
It will also prevent the pads from sliding in and out well. This can result in poor braking.
 
Replace the old pins with this set of stainless steel Brake Pad Pins with a Hex head, very easy to remove with your 8mm socket and no risk of stripping the head!
 
Those pins are made from quality stainless steel to resist the mud, grit, and salt you will encounter on your adventures. This is set with one front and one rear brake pad pin for your DRZ-400S.