Dear Car Talk:

I had my 2002 Lexus' tires rotated at the dealer. They inspected my brakes and told me that the front left was only a 2, but all the other pads/brakes (right front, both rear) were fine, at 7. So I took my car to another garage to see if I could get a better price on the front brake job. They did a full brake inspection and told me that not only did I need front brakes, but I needed rear brakes as well, since all of my pads were at 3. Very confusing. So I went back to the dealer. He had a different mechanic inspect the car. This second mechanic told me that yes, the front brakes should be replaced (which I knew) ... and then told me that my left rear pads were a 4, and my right rear were a 7. How can there be such discrepancies between the two garages concerning the measurements of my rear brake pads? I had only the front brakes fixed. Should I have done the rear, too? The dealer told me I probably could wait another 10,000 miles before doing the rear brakes.

-- Robinson

The reason the numbers can be different is because they're all subjective. For instance, some girl on the beach might have seen my brother back in the day and said, "He's a 10."

Actually, that's a bad example. No one ever said that. Only twice in his life did he ever get a rating as high as a one-and-a-half. And he married both of those girls. But you get the idea.

The numbers represent the amount of life left on the brake pads. But they're just estimates, made by a mechanic who uses his eyeballs, not the Hubble Space Telescope.

So a 5 means the mechanic estimates you've got about 50 percent of the pads' life left. In which case, there's no need to replace them.

Whereas if you're at a 1 or 2, meaning you have 10 percent to 20 percent of pad life left, that means it's time to replace the pads.

So your dealer was right that, since your front left was a 2, it was time to replace the front pads.

But what concerns me is the discrepancy between the front left and front right pads. If the left front was a 2 and the right front was a 7, that suggests to me that there's something wrong with that left front brake.

Something is keeping that left front brake applied, even when your foot is off the brake pedal. It could be a sticking caliper piston, the pads sticking in the caliper bracket or a crimped brake line. But that needs to be checked out. Otherwise, those new pads on the left side will wear out too quickly, too.

So ask the dealer to take another look for you, and see if he has an explanation for why the left front wore out so much faster than the right front.

And even if he can't come up with anything, when you go back to get the rear pads done in 10,000 miles, have them check the fronts again. And if the left is wearing faster than the right, insist that they do some more investigating.