I admit, I’m learning as I go here. I’m trying to learn how to work on my Dad’s truck and I’m having a brake issue. Brake lines are new and brakes were working fine. Normally, They only have to push the brake pedal down about halfway before brakes start to engage. Today I got in it and backing out of the driveway I had to push the pedal all the way at to the floor for the truck to stop. What should I check first?