I just replaced the master cylinder. And now my brakes are still soft going about ten to fifteen mph the stop ok but the greater the speed the worse they get at not stopping
My car has 300000 miles.
My car has an automatic transmission.
When you say (and now my brakes are still soft) this means you had soft brakes before and after the master cylinder was replaced. If you have soft brakes, it is caused by air in the brakes, problems with flexible hoses, calipers binding, and rear calipers not adjusting and traveling excessively. You will need to have all these possible problems checked to completely diagnose the brake problem you are having.