How do I know if tire rod end is bad?

checking the wheel for vibration an up and down movement its a bad bearing from side to side its tie rods you shouldnt have any play on those things what your problem is that you have wrap rotors when you break that's your sign that tells you its the breaks and not the tie rods

if it vibrates when you hit the brakes, its not the tie rod, a tie rod would make a noise all the time or over bumps.

you can test a tie rod to an extent, at least the ball joint at the end of it. with that tire off the ground, and the sterring wheel locked, move that tire back and forth like it would for a turn. it should not move much of at all. if you heara click or get much motion, then that ball joint is bad. the bad thing about that is tthat you have to have the joint replaed and an alignment done.

jack it back up look at the tie rod wile wheel is moved in & out .the tie rod should not have any play with the spindle horizontally , or lateral play push up and down to check . if its is bad change both sides. you also have inner sockets ( inner tie rods ) inside the bollow on the rack & pinion, if outer tie rod checks out ok and you have play the inner socket are bad

yes have someone move the tire while you look at the tie rod end,if it's bad you should be able to see movement in the joint itself,check both inner and outer ends

well, without you taking it to an alignment shop, the way you did it is the only way I can think of. Also, eye ball it and you should be able to see grease and what not.