Dear Jim,

The brakes on my 1997 Pontiac Grand AM (3.1L, V6) have been acting funny the last couple of days.

Usually, when I'm sitting at a red light for a couple of minutes, the pedal goes all the way down to the floor. It feels like the brake is deflating, and the pedal becomes way too easy to press.

If I pump it up and down a few times, it feels normal again, but only for a while. Are the brakes about to go out completely?

-- Coley Berg

Probably not, bro, but this problem is a perfect illustration of what I said about funny-acting brakes in last week's column: Take it as seriously as a skydiver takes a funny-acting parachute.

Sounds like the trouble here is with your master cylinder, which controls the flow of hydraulic brake fluid to all four wheels. It's a cleverly designed, safe device that uses what's called a dual-tandem system, which simply means it's separated into two sections.

One controls flow to the front wheels, while the other handles the back ones. In other words, if one fluid line springs a leak, you'll still have braking power for two wheels -- a big reduction in braking efficiency, but still enough to stop the car.

Normally, that pedal is firm when you press it because you're increasing the hydraulic pressure in two good lines. In your case, the pressure is being lost in one line, so you're having to step down farther to make up for it and still get enough braking pressure in the one good line that's left.

Of course, there's still a leak in the system, which is why the pressure falls back down after a few minutes, as it's doing when you're stopped at a red light.

Pumping the pedal draws more reservoir fluid into the lines, which brings the pressure back up temporarily.

Bottom line, brother: Get the master cylinder replaced right now. Like I say, that dual-tandem system means you're not likely to lose your brakes completely, but your stopping power is severely compromised at this point, and that's very bad for you and everyone else on the road.

Tip of the Week:

If you're adding brake fluid, drivers, don't leave the cap off the reservoir (or the bottle) any longer than necessary. The stuff loves to absorb water from the air, which can quickly degrade its effectiveness in your system.

Buffalo Jim, owner of Allstate Auto & Marine Repair in Las Vegas, writes a weekly column. Send your automotive questions to him at buffalojim@lasvegasniftynickel.com. If Jim picks your question to answer in Nuts & Bolts, you'll also be the proud recipient of a deck of official Buffalo Jim playing cards, presented in a classy, tin box bearing his hairy image.