I have a 97 bonneville. The brake work some times and other times the peddled goes all the way to the floor. Was thinking it could be the master cylinder. Thanks for any help.

Sounds like a bad master cylinder. Check the fluid level to make sure.

When it goes to the floor, does the pedal get hard when you pump it several times, or does it just keep going to the floor?

when it goes to the floor it will not pump up. some times the whole pedle with be there and some times there is nothing. The brake fluid level is fine.

Sounds like a bad master cylinder. Is there any signs of leaking? Either under the car or in the master cylinder area. When you fill the fluid up, does the level drop over the next day or so? Look where you regularly park the car to see if there is evidence of fluid drips or pooling on the ground.

there is not any leaks that I could see. I do most of my own mechanical work. I have looked at all the lines and have seen no leaks. I have not added any fluid, the level stay the same.

Sounds like a bad master cylinder to me, but I would like Danthurs opinion.

I'm throwing my two-cents in - Master cylinder. A spongy, soft brake pedal that goes all the way to the floor and wont pump us with no leaks is a bad master cylinder.

Yep and they can fade in and out. Get it replaced before you have 0 brake when you need more than usual.