Hi everybody! Last night I was coming to a normal stop and my 2005 MCS decided not to stop. I know how the normal brake pedal is supposed to feel, and the pedal last night was not only soft, but it was spongy. In order to stop, I did have to depend on down shifting. If I really needed to, I would hit the pedal really hard, almost to the floor, then it would stop. I have had experience with this in a 1968 Camaro, only to find the master cylinder was bad.

Anyway, all the other threads I have seen even remotely similar, include circumstances where the owners just got done changing the pads and rotors. My car hasn't had any brake work since I had it. I've put about 10k miles on it since I bought it, putting it at 50k.

Anyway, what could have went wrong? I'm obviously not driving it again until I fix it. Thanks for the help!

 

First thing would be to get the brake lines flushed. That should be done on a regular basis just like engine and gear box, only at about 20K miles or every couple of years. During that process the master cylinder and associated hardware can be checked over. Just normal maintenance will solve a lot of problems before they start.

 

Was it wet out?
Very wet brakes can sometimes feel soft, or grabby depending on a few factors...
If you were doing multiple repeated stops...than they might have gotten HOT...then a FLUSH would fix it...dot4 fluid is only good for about 4 years....gets waterlogged and boils faster than the dot3 stuff in older cars...
I would check the fluid level ASAP...the color here can usually help...it tends to darken as it ages...so if it looks kinda like maple syrup dark, its pretty old (some can be blue, etc).
It is possible you have a bad master,a leaking line, or even a bad caliper...
Gotta look!! Or just get a "free" inspection at one of the local places....mini brakes are pretty standard....and most any decent shop CAN do a good job, one of the few things on our car that anyplace can work on competently!!