Dear Car Talk:
I have a 2009 GMC Envoy with 53,000 easy miles. All recommended services have been done at the appropriate time/mileage. Twice recently, I have experienced what I think is sticking brakes. This has occurred in traffic situations, like when I stop at a light, and lasts about 100 feet, and then releases. I brake with my left foot, which I know is not recommended, but this is a long (over 60 years) habit. I think it could be the anti-lock-brake system working, but it remains "locked" after I remove my left foot and try to accelerate. I have not gone to the dealer yet (it's still under extended warranty). As I stated, this has only recently occurred. I'm guessing it's brakes and not transmission or transfer. Any thoughts? Thanks.
It could be an ABS problem. Could be a sticking caliper. It could be a transmission issue -- if there's a delay in getting power to the wheels, that can feel like a brake problem. But my first guess would be a faulty power-brake booster.
The booster takes the force of your foot on the brake pedal and "boosts" or multiplies it, sending much more force to the brakes themselves.
That's the "power" in "power brakes." It's what allows you to use a modest amount of force with one haven't-been-to-the-gym-in-30-years foot, and stop a 5,000-pound rolling hulk of steel (or steel and rust, as was always the case with my brother). But if the booster is getting stuck in its boost mode, it will continue to apply force to the brakes, even after you release the pedal.
And it's not unusual for a faulty booster to stay on after a full stop, and then release itself. So the symptoms make sense.
The booster is easy to test. If you want to do it yourself, have your dealer show you where the vacuum hose goes into the booster. Then, the next time your brakes lock up, pull over and disconnect that vacuum hose. If the brakes free up, bingo -- you need a booster.
But it could be a master cylinder, too. Or any of those other things I mentioned. So since you're under warranty, why not let your dealer crawl under the truck and get his shirt dirty? You paid for the extended warranty. Go ahead and use it.