2000 Lexus GS 400 Constant warped rotors

Does the warpage reappear right after machining the rotors or does it take a while? One of the biggest causes of this problem if it takes a while to show up is failure to use a click-type torque wrench to tighten the lug nuts. We all laughed at a coworker in the mid '80s who started using a torque wrench until the rest of us started having comebacks for pedal pulsation on light front-wheel-drive cars. Since then, we all use them on every car. Unequal clamping forces cause the warpage when the rotors heat up and cool down numerous times.

If the warpage shows up one day but wasn't there the day before, one possible thing to look for a missing or bent splash shield behind the rotor. This is more common on Fords with plastic shields that break off.

When the rotors are machined, is someone cleaning off the round rust spots on the mounting surface? If not, warpage can be machined into the rotor if the cone rests on that spot on the lathe. If the rotor is installed in a different orientation, that rust spot will hold the rotor from sitting flush on the hub. You will see that in the wheel and tire too if you run it jacked up.

If the pedal pulses during braking, the rotor thickness has variations. That is due to a machining setup problem or rust has flaked off, then the rotor wore smooth. If the steering wheel shimmies, look for a caliper that can't slide on its mounts freely. Those caliper to mount surfaces must be cleaned and lubricated with special high temperature grease. Holler back if you've checked these things already.

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Ok, if it's always there, could it be something other than the rotors? Do you have and / or know how to set up a dial indicator to measure sideways runout of the hubs? I don't want to bore you with stuff you already know. Even before you get that far, jack the car up and spin the tires by hand or by running the engine and watch the tire tread. If it squirms back and forth sideways or there is a noticeable hump, there is a broken tire belt. If the wheel also wobbles, the wheel could be bent. Neither of these are caused by the rotors. You should feel these problems even when not braking.

If the tires and wheels are true, remove the wheels and put the lug nuts back on with washers to hold the rotors tight, then use the dial indicator to check for rotor runout. Check on the wheel contact area and on the braking surface. If you see excessive runout on the wheel contact area and about twice as much on the braking surface, it is more likely ther is rust or other debris between the rotor and hub, or the hub is bent.

If the dial indicator shows very little runout on the wheel contact area but there is runout on the braking surface, the rotor would appear to be warped. A sticking caliper would be the most likely suspect, but since you already replaced them, look closer at using a torque wrench.

One other thing to consider is to press the brake pedal while the front wheels are off, then run up front and see if you can turn the rotors by hand. (Take your foot off the pedal). If you can not, open the bleeder screw and see if it releases. That will give us a bunch more to discuss.

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