About a year ago I installed new front callipers. Since then, I have kept driving it although it stops fine. However, while sitting at a stop light, I can feel the pedal sink down and sometimes I have to shift to neutral and take my foot off the brake to let up and push it again, and it will sink down.

Do I just need to bleed them better or is it a bad master cylinder? What are the symptoms of a bad master cylinder? THANK YOU for your help.

 

You are not losing brake fluid, correct? First try rebleeding all four wheels in the correct sequence. If that doesn't work, then replace the master cylinder.

 

I'm pretty sure it's the master cylinder. If there was air in the LINES, I THINK it would have problems when I apply the brakes initially. The brakes stop the car perfectly even as of now.

Anyways, how do I replace the master cylinder? Looks like two bolts to the firewall, disconnect two fluid lines but what do I disconnect when it comes off the firewall? Thanks.

 

Making a normal stop then the pedal slowly sinking down is usually a bad master cylinder. Either that, or a leak to outside, which you would notice because it would run out of brake fluid.

To replace the cylinder simply remove the lines and the nuts holding it to the brake booster and pull it off. There is nothing to disconnect inside. The booster has a rod which pushes on the plunger in the cylinder. If fluid has been leaking out of the back of the master cylinder and getting into the booster, the rubber parts of the booster will soon be ruined and it will quit working. Might as well replace it now if that's the case.