Q: I have a 2005 Jeep Grand Cherokee with 160,000 miles on it. The problem is with the brake rotors warping. Every time I've had the brakes worked on, they start to pulsate again after a few thousand miles. Last time the dealer installed new pads and rotors but the same thing happened. Are there certain types of rotors or pads I can use to prevent this?
A: First, let's review the primary causes of brake rotor warping — excessive heat or manufacturing defect. Seems unlikely you and the many other Jeep owners who've complained about the same problem would continually get faulty replacement rotors.
Thus, focus on excess heat. If a driver consistently brakes late and hard for stops or drags the brakes while driving, the heat buildup in the rotors can eventually cause distortion, uneven wear and warpage. Always brake early and brake lightly whenever possible. And here's a little tip. Once stopped for a light, let the car roll a foot or so forward to move the pads off the "hot spot" on the rotor. During a long stop, do this a couple of times — safely, of course. This reduces "heat soak" in the rotors, where one section is significantly hotter than the rest of the rotor.
Design, manufacturing and mechanical issues can certainly contribute to warped rotors. Undersized calipers and rotors may not be able to dissipate heat fast enough during aggressive braking to prevent eventual warpage. Better-quality replacement rotors and pads may help this type of issue. If a mechanical or hydraulic issue is preventing the brake proportioning valve or rear brakes from doing their share, the front brakes can be overworked and overheated in "normal" driving.
Sticky caliper pistons and/or binding caliper slider pins are a primary cause of rotor warpage and uneven rotor wear. An often overlooked cause for warped rotors is improper or uneven torque on the wheel lug nuts. Always — every single time — make sure the wheels are tightened in a symmetrical order in stages to the proper torque specification. Similarly, rust or corrosion between the hub face and rotor can lead to uneven brake wear.
Remember, you will feel a vibration in the pedal or steering wheel when rotors have much more than two-thousandths of an inch of lateral run-out — that's .002"!
A final thought. Proper rotor and pad "bedding" or break-in when new can significantly affect brake performance and life expectancy. Here's how I do it: Find a lightly traveled 45- to 50-mph road. With no vehicles behind you, accelerate up to 45 mph, then brake very firmly down to rolling speed. Repeat this a few times until you smell the tinge of brake heat or feel the beginning of brake fade. Then just cruise along at the speed limit, allowing the brakes to cool back to normal temperature. This process "beds" the brakes, making the pad and rotor surfaces "happy" with each other. Once properly bedded, the brakes should perform well for their full service life.
Q: Need some advice for my daughter and her husband. They bought a 2006 Nissan 350Z — smart folks, 'cause they won't let me drive it. No problems with it, but a headlight quit working. The Nissan dealer wants $1,300 to replace it. Any comment or suggestions? This seems sort of excessive.
A: I'd suggest that you offer a much less expensive fix in exchange for driving privileges! According to my ALLDATA automotive database, this Nissan is fitted with xenon HID headlamps. Nissan service bulletin NTB10-061A dated June 2010 suggests that a failed headlamp bulb, about $180, or HID control unit, $400-$500, is the most likely cause of an inoperative headlight. Even with an hour or so of labor, that's a far cry from $1,300 to replace the entire headlight assembly. There's a very good chance you can solve the problem, save them money and, most important, end up with driving privileges! Remember, I'm an instructor for the Skip Barber Racing School — you'd have lots of fun learning how to properly drive that performance car!