I have recently changed my brake system which included, calibers, rotors, lines, brakes. Since I did this change, I was losing brake pressure in the lines so I changed the master cylinder. I have changed the master cylinder 3 times, and this last time, it lasted a little longer, but now I have noticed that on 2 ocassions as I was backing up, I lost my brakes and I also feel the brakes sometimes becomes spongy. I also feel as I brake, the peddle sometimes goes down then I feel the peddle pushing back up. What could be causing this problem, since I have changed everything that I know in the brake system?
Please Help!!
Thanks!!