DEAR CAR TALK: My problem is, I have a 2004 Silverado 4WD Z71 that I bought new, and over the years, the brakes have gotten terrible. I’ve been through the typical brake failures from rusted lines over the past six years and survived them all. So far.

I love the truck. It still drives and handles well. The problem is that the brakes have no braking power. I have replaced all four rotors, the rear calipers, the brake booster, as well as the master cylinder, and, of course, all pads have been replaced at different times as they wore out. This truck will not lock up the brakes from any speed (barely on gravel).

The only thing that has not been replaced are the front calipers. Could they have lost power over the years, even though they never stick?

I wouldn’t mind spending $400 to $500 more to get “like new brakes,” but I hate to spend it if there’s no guarantee of success. Any ideas? – Greg

RAY: Well, one more untimely brake failure, and you could be looking at a 2017 Silverado, Greg. That’s one idea.

Actually, disc brakes aren’t supposed to lock up. But we’re going to accept that the brakes are not as good as they used to be. So my first idea is to make sure there’s no air in the brake system.

You say you replaced the rear calipers. A lot of people don’t know that after replacing the rear calipers, the brakes at all four wheels need to be bled. If there’s some air trapped in the system, that would certainly diminish your braking power. So bleed all four calipers, if you really know what you’re doing. Or pay someone to do it for you if you’re not sure.

We use something called a power bleeder at the shop, which pressurizes the master cylinder. That makes the job pretty much foolproof, as long as you can count to four – which five out of seven of

While you’re bleeding the calipers, my second idea is to take a look at the wear on the pads, particularly at the front. If the front caliper slides are not working correctly, you’ll often see more wear on the inner pad than on the outer pad. Those slides are supposed to pull the two pads together around each rotor.

But if only one pad is doing all the work, the truck will take longer to stop. And since the front wheels do most of the stopping, bad caliper slides could make a big difference.

But I wouldn’t go spending hundreds of dollars to change the front calipers without evidence that they’re faulty. Check the pad wear first, and see if the evidence is there.

Finally, even though you replaced the power brake booster, it’s possible that the booster isn’t getting enough vacuum. There’s a hose that runs from the engine manifold to the booster that could be collapsed or something.

You can go to the auto parts store, take that hose off in the parking lot, ask them to sell you a replacement, and then put the new one back before you drive home. It’s cheap and easy. And you’ll know right away if it makes any difference.

In the meantime, wear sneakers so you can open the door and drag your foot if necessary. Good luck, Greg.

Got a question about cars? E-mail Car Talk’s Ray Magliozzi by visiting the Car Talk website, www.cartalk.com.