I have a 2008 Infiniti g37 coupe with 111,000 miles and twice now in Stop and Go traffic my brake pedal has gotten STIFF and the car did NOT stop. I was lucky eventually brakes came back but twice now the car's brake pedal felt similar to it does when the car is OFF and you pump the brakes, soon it locks up and does not go in.

Any idea what it could have been, brakes are fine now and stopping just fine @ 6-mph and in stop and go both... thank you,

Shane

 

Not sure what exactly is causing the problem, but with high mileage cars like that, you might want to check the entire system. Flush/change brake fluid, check rotor surfaces, check pads, check your brake lines, too.

 

My guess is a bad brake booster. But as said above check everything and flush the fluids.

 

That was my first thought as well; sounds like he lost vacuum...

 

You might want to check out your master cylinder as well..