When you bleed brakes how can you tell when there's no more air in the brakes lines, also?

i'm gonna change my 2 front calipers do i need to bleed all 4 brakes or just the front 2When you bleed brakes how can you tell when there's no more air in the brakes lines, also?the rear brakes are most likely drum brakes which are cable operated from the e-brake ( depending on what type of car )..

If you have never done it i would suggest to leave it for someone who has, but to answer the question, the bleeder valve will bubble with air, all you do is just keep repeating the process until nothing but brake fluid comes out, be sure to close the valve before the brake pedal hits the floor so no air gets in, if you want a complete guide on bleeding the brakes let me know...When you bleed brakes how can you tell when there's no more air in the brakes lines, also?For the cost of brake fluid bleed all four. That way you will have fresh fluid. I always spray some WD 40 or penetrating oil on the bleeders the day or two before. Start with the furthest brake from the master cylinder first and then the next. Your successful when no more air comes out of the lines and you have a firm pedal.When you bleed brakes how can you tell when there's no more air in the brakes lines, also?If it were me, I would bleed them all, because I would change all the brake fluid as well. Why put old brake fluid in new calipers?When you bleed brakes how can you tell when there's no more air in the brakes lines, also?once the fluid comes out without bubbles in it there shouldn't be any air left, while you bleed them however, be sure the master cylinder stys full. yes you should bleed all four just to be safe.When you bleed brakes how can you tell when there's no more air in the brakes lines, also?you hook a vacuum hose to the bleed screw and get an empty coke bottle and pour brake fluid in the coke bottle make sure that the hose extends into the brake fluid inside the bottle because when you release the brake it takes a vacuum and can pull air instead of brake fluid, every time you depress the brakes there will be bubbles coming out and when it stops coming out you have successfully bled the brakes. BUT remember you have to keep the master cylinder full of brake fluid so it will not suck in air, and you have to lightly press the brake pedal all the way to the floor and let up on it easy because it causes a surge and will spray brake fluid everywhere. GOOD LUCK!!