Continued: Brake-rotor wear may lead to vibration

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Q I have a 2000 Saab 9-3 with the 2.3-liter turbo motor and 84,000 miles. When I brake from a higher speed, say above 50 miles per hour, the steering wheel vibrates. The vibration will settle down as I slow down, and it stops when I get below about 30 mph.

I don't feel any pulsating on the brake pedal, which I thought would indicate warped rotors. Brake pads are good. I checked the front of the car for any ball-joint play; everything seems tight. I also checked for a bent rim by rotating the wheels while the car was lifted, and they look straight. Tires show no strange wear patterns, are in good condition, and were recently balanced.

Maybe this is a worn-out front strut causing a bouncing of the front tires? Or maybe the ball joints should be checked more closely? I've felt warped rotors before, and this vibration does not have the same feel.

A The rotors may not be warped, but I'll bet they're worn. Check for a ridge or groove at the outside edge and inside hub of the rotor. Modern brake pads are more aggressive and actually wear the surface of the rotor. No problem -- until the brake pad steps up on the ridge as you brake and doesn't seat properly on the rotor surface.

I discovered this issue years ago on a 5-Series BMW. To confirm the vibration, I had my wife hold the steering wheel while I leaned out the driver's window far enough to see the left front wheel as I braked firmly. Then I had her drive and I leaned out the passenger window far enough to see the right front wheel as she braked firmly. The right front wobbled noticeably, and upon inspection, I found significant wear on the inner and outer surfaces of the front rotors. New rotors resolved the vibration.

Other possible sources for the vibration include rotor thickness variation -- again, from wear -- and corrosion on the mating surface between the rotor and hub.

Q I have a 2000 Dodge Dakota. It has a noise in the steering column that can best be described as a moan-and-groan sound. It has been there for quite a while, and I have taken it to several mechanics, but no one seems to know what to do about it. A few years ago, a very minor amount of fluid came out of the column where the gearshift is.

A I have no idea what that fluid may have been. Power steering fluid doesn't enter the steering column, but the power steering pump is often the source of a moaning sound as you turn the steering wheel. Try a power-steering fluid additive to see if this quiets the noise.

Chrysler issued a service bulletin, 19-04-00, dated June 2000, suggesting replacement of five screws in the steering column to address a "squeaking/creaking sound" in the steering column as you turn the wheel.

Q Before leaving for a trip, I usually check the tire pressure and make sure the tires have 32 pounds per square inch (psi) of pressure. I am wondering what the tire pressure might go up to after being on the highway for 30 minutes.

A Depending on the vehicle, load, speed, road surface, ambient temperature and other factors, you might find that the tire pressure has climbed 4 to 8 psi after sustained highway driving.

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