Please help...brake pedal vibration

[90sabre]

I have a 98 Lumina LTZ Sedan that my wife mainly drives. Since we purchased it about 2 years ago, there has always been a fairly heavy vibration felt when the brakes are applied. The vibration is only felt by the driver but to me seems excessive. We've taken it to a couple shops and have been told that it's normal for an ABS car. Any thoughts on this? How much vibration is normal? Also, when it is raining heavily the brakes sometimes take a second to "kick in" before slowing the car.Is this normal?
Thanks in advance for any help.

Leo
1990 Buick LeSabre Limited
1998 Chevy Lumina LTZ Sedan(3800)

[Manny_boy]

Whatever shop told you that it was normal, don't go there anymore...

The only time ABS makes your pedal pulsate should be during a panic stop. If your pedal is pulsating under normal braking, it means that more than likely, your brake rotors are out of parallel (warped). Either have them turned at a reputable shop (some mechanics will advise against it though), or depending on the price of your rotors, sometimes it's just better to buy new ones.

What kind of pads do you use? If you are using ceramic pads, when it is cold and wet outside, yes, they do take a second before they grab hold. If you are using regular old organic type autozone pads, stop. Try fitting your car with some performance friction pads, you will notice the difference.

[jeffcoslacker]

Originally Posted by Manny_boy

Whatever shop told you that it was normal, don't go there anymore...

The only time ABS makes your pedal pulsate should be during a panic stop. If your pedal is pulsating under normal braking, it means that more than likely, your brake rotors are out of parallel (warped). Either have them turned at a reputable shop (some mechanics will advise against it though), or depending on the price of your rotors, sometimes it's just better to buy new ones.

What kind of pads do you use? If you are using ceramic pads, when it is cold and wet outside, yes, they do take a second before they grab hold. If you are using regular old organic type autozone pads, stop. Try fitting your car with some performance friction pads, you will notice the difference.

My LS with alloy wheels does that if the lugnuts aren't properly torqued. It's fairly common on these. I was having the same problem, and realized that I didn't go over them with a torque wrench after the tire shop put the new tires on. I loosened them all and torqued them properly to 100 ft lbs, the pulsation is now gone.

The alloy wheels, being softer and less rigid than the steel wheel, don't spread out the clamping force of the lugnuts as evenly as steel wheels do, causing the brake rotor to be unevenly clamped if the lug torque is not uniform, which causes distortion of the rotor.

Try this first before you change any parts.

P.S. Tire shops will tell you the torque sticks that they use on their impact guns torques the lugs evenly, my experience says otherwise.

The guy that put my tires on used one, and when I loosened them to re-torque them properly, I found as much as 40 ft lbs variation from lug to lug. Do it with a good torque wrench. If you don't have one, rent one free from Autozone.