Did you replace these parts to try to solve the noise or did the noise start after the parts were replaced? Most commonly what causes this symptom is a warped rotor coupled with grooves worn into the mounts the pads rest on.
The least likely time to find a warped rotor is after a used one has been machined. Then it is causes by an incorrect setup on the brake lathe to include not cleaning off the one or three small round spots of rust that build up on the rotor-to-hub contact point. That rust will prevent the rotor from sitting squarely on the lathe, and a warp will be machined into it.
The most likely time to find a warped rotor is when it is used and has been in service a while. The next most likely time is when a new one is installed that was made in China. There's nothing wrong with their quality, but when we make parts from cast iron, we let them sit for up to three months to "age" before they get their final machining. The Chinese cast 'em, pack, 'em, and ship 'em, then they age on your car. Warping is common and a light machining will take care of that. Usually that doesn't happen right away. It typically takes from a few weeks to a couple of months to show up.
Also don't overlook rust or debris that was stuck to the hub and is sandwiched between the hub and rotor. That will prevent the rotor from being clamped perfectly parallel to the hub. To identify these conditions, raise all four tires off the ground, remove the wheel, then reinstall a few of the lug nuts. Run it in gear and observe the caliper. If you can see it walking sideways back and forth, the rotor is warped or not seated squarely by quite a bit. If you can't see anything obvious, you'll need a dial indicator to measure the lateral run out. Anything over about.005" is enough to warrant looking for the cause.
Check the knuckle too for grooves worn into them where the pads make contact when the bakes are applied. I have repaired a few with a wire feed welder by filling the grooves in, then grinding the surfaces smooth, but that takes a long time because the metal has to be preheated first. For some vehicles there are stainless steel repair inserts. You can grind the high spots down too but while that will stop the rotational clunking, you'll usually get a single clunk each time the brakes are applied right after changing direction, (drive to reverse), because the pads can move further before they bottom out against the mount.
To reduce the formation of those grooves, professionals lubricate the surfaces with a special high-temperature brake grease. Very few do-it-yourselfers know to do this. One of the biggest causes of warped rotors is failure to use a click-type torque wrench on the lug nuts. Proper torque is needed to provide even clamping forces on the rotor, to prevent damage to the threads which will show up the next time someone tries to get that wheel off, (and that person will be blamed unfairly for causing the damage), so the wheel won't come loose, and so a 90-pound woman can change a flat tire.
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Thursday, October 23rd, 2014 AT 11:09 PM
