Why does my car vibrate when I apply the brakes?

I have a '06 Chevy Cobalt LS and I recently put after-market wheels on the car. The stock tires fit the wheels and I picked the wheels because they are made to fit a '06 Chevy Cobalt (with 4-lug, 15" x 6.5" wheels). Now when I apply the brakes at speeds above 30 MPH, the front of the car shakes as though the ABS system is kicking in. It quits after the car has slowed to speeds under 30 MPH.





The wheels do not appear to be rubbing on the calipers. The wheels were electronically spin balanced at Discount Tire Co. where I purchased them.|||Your wheels are improperly torqued. They must be torqued to the proper amount in the proper sequence. This is true for all wheels and vehicles but is much more critical with disc brakes.When torqued improperly, the rotors will flex and warp. If they warp more than a few thousandths of an inch you can get an immediate pulsation in your brakes. If you properly retorque them before measurable wear occours you can get rid of the pulsing that way. But, if you have driven enough the rotor will wear unvenly making tiny variations in thickness. Disc brakes cannot have more than .0005" thickness variation. If this has happened and you have this all you can do is replace or machine the rotors. I would suggest replacement on such a new vehicle because rotors are not made like they used to be and they wear more because of the harder metal pads.|||Probably it's loose and that in fact is causing it to vibrate. Generally speaking things that are tight will not rattle.|||Brake rotors (look like an "old" 33 rpm record) are discs. When they heat up they sometimes warp (like that old record did)..when you step on the brake to stop the car the rotyation of that warp makes your foot and pedal feel like it goes up and down...replace or "resurface" the rotors and you should be ok. You might have to replace the brake pads as well.





You may also feel it in the steering wheel, too.|||you might have a bent wheel or you got a disc out of round.|||MAYBE YOU LOST A WHEEL WEIGHT. GET THEM CHECKED. I WOULD ALSO CHECK YOUR BREAKS AND ROTORS.|||SOUNDS LIKE THE FRONEND IS OUT OF LINE|||The car did not have this problem until you put after market wheels and Stock tires on, so therefore I believe your problem lies with the wheels and tires, not the brakes, although if brakes did become part of the problem then it was due to having a incompatible wheel and tires that affected the brakes.|||Most likely when the new tires and wheels were put on they used an air wrench unfortunately. This will unevenly torque the lug nuts and lead to very rapir warpage of the rotors. Once they are warped the brake pads ride up and down on the hills and valleys as the rotors turn with the wheels. At low speed it is not terribly noticable when you are braking as the transition between the high and low points on the rotor is slower. Braking from high speeds, however, the transition is much faster as the rotor is turning faster, and it feels like a vibration, sometimes quite a violent one.





I am afraid that at the very least you will need to have the rotors turned (machined back to flat), or if they are too badly warped you will have to replace them. In either case, when they remount the tires insist on having the mechanic use a torque wrench to tighten the lugs to spec and to do the job by hand, not with air wrenches to avoid this problem in the future.





This happens quite often I am sorry to say at shops that try to save time by using air wrenches on wheel mounting.|||When you apply the brakes and have a brake shake, rotors are warped, usually caused by excessive heat and hitting water when they are hot.|||I would have to say that they overtightened the lug nuts and warped the rotors.