Months after a new installation of brake pads
and brake rotors
a pulsation in the pedal has slowly developed. There is very little wear, and there are no visual indicators of a problem. The brake pads
are worn evenly, brake rotors
look clean with no corrosion.
Measuring the lateral runout and disc thickness variation will give you a better idea of what is really happening. This runout can originate from improper brake hardware
maintenance, corrosion and debris on the hub mounting flange, or even improperly tightening the lug nuts. The average maximum allowable runout is between 0.001" and 0.003" with some manufacturers specifying 0.000" of allowed runout. Runout can create thickness variations in the brake rotors
which will lead to problems with uneven wear and pulsation. This type of problem is not to be confused with warping caused by heat distortion.
If a brake rotor
has a high-spot of lateral runout, that point will circle past the calipers
hundreds of times within just one mile, multiply this over thousands of miles, and that point will have scraped the brake pad
millions of times. This seemingly small problem can cause enough of the rotor
to be removed over time that a variation in thickness can be felt by the driver.