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Re: Quick brake question Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Wed, 10 Apr 2002 15:34:17
In Reply to: Quick brake question, JVD, Wed, 10 Apr 2002 13:01:00 Members do not see ads below this line. - Help Keep This Site Online - Signup |
I would assume they meant that there was 30% of the pad remaining.
Three things can happen to rotors - they wear, they wear unevenly, and they warp. Uniform wear is normal. When the pads are replaced, the rotors should be inspected for wear. There is a minimum thickness for the rotor (stamped right on the edge), and if it's too thin, it should be replaced. It's really hard to wear out a rotor, unless they get turned at least once. See below.
Rotors will wear unevenly - you'll see little grooves in the face of the rotor. This is normal. Some shops ALWAYS turn the rotors to remove these grooves. Turning the rotors means they put them on a machine and basically sand the faces smooth and parallel. You take a grooved rotor and make a nice, pretty surface. This removes lots of rotor material, and sometimes in order to get a nice, smooth, face, they need to grind the rotor below the minimum thickness. Under those circumstances, the shop will tell you that you need new rotors. A little uneven wear won't hurt your braking any. Big, nasty, grooves aren't good, but small ones are OK.
Lastly, rotors warp. Think of a warped record. (does anyone remember phonograph records?). Rotors warp if the lugnuts are improperly tightened, or they get really hot then cooled quickly, like going through a puddle. The more rotors get turned, the thinner they get, and the more likely to warp. You can tell warped rotors - when you press the brake pedal, you feel a pulsing in the pedal as the brake pads grab the high spots and glide over the low ones. It makes sense to turn rotors if they're warped.
OK, so what? Many brake shops grind rotors as part of every brake job. Not only can they charge for the task, but there's a good chance the ground (turned) rotor will be below the minimum thickness, and they can charge you for a new one. Turning rotors is about $20 each; replacement rotors for a Saab run about $80 for the fronts.
As a data point, I've NEVER had to grind a rotor on any of my Saabs. And I've owned these cars for hundreds of thousands of miles. Yes, the rotors have a few grooves, but they still work fine. They are nowhere near the minimum thickness, and I've never had a warped rotor. Unless you're running some super-hard metallic racing brake pads, braking won't wear your rotors down to the minimum, not unless you put 200K city miles on the car. Rotors get to the minimum because they get turned a few times.
Unless your rotors are warped, or VERY badly grooved, I don't turn or replace the rotors.
As a recommendation, changing brake pads is actually one of the easier do-it-yourself tasks. Not only will you save GOBS of money, you also get to peek around under the car, and notice if anything else needs work, or is fine. Get yourself the Haynes manual, a set of jack stands, and go to town. Yes, it'll take you longer the first time around than going to the shop, but after that, it'll be cake.
Good luck!
posted by 140.157.4...
, Wed, 10 Apr 2002 15:34:17 <-- Viewing This Message, Thu, 11 Apr 2002 13:18:49
, Wed, 10 Apr 2002 21:12:01
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