So, I'm desperate! I'm a motorcycle guy myself, and I know far less about cars even though I've had a few. I've owned an M3, a WRX, and currently a 350Z- I'm afraid to post this here on a Cobalt forum, but I've never been an American car guy. I've always thought reliability and quality was significantly lower, and always stick to buying foreign. I'm sorry! Anyway, my girlfriend has an 07 Cobalt LT with exactly 50k. There are a couple problems with it.

Firstly, when you brake the car will shake really violently. If you're going about 5 miles an hour, it sort of wallops every second or so if that makes sense. Pretty much the telltale signs of a warped rotor. I took off the wheels and inspected the rotors a best as I could, and didnt see any sort of indication of warping. My next guess was that possible some of the bolts had been overtorqued on the last tire change, but that wasn't it either. Anybody have suggestions or similar problems?

My second question is more recent. The car has a gradual humming sound from about 35mph+. The faster you go, the louder the humming. It isn't RPM related and it's definitely coming from the front left side of the car. I'm not sure if they're the bearings, the tires, or what. Like I said, I know really little about cars! I do know that I've never had to change a bearing in 50k.

I really appreciate the help you guys might have, from my experience the forum guys are usually the best people to ask. Thanks!

 

the shaking could be rotors, inspecting them by eye isnt enough as the smallest amount of runout can make a huge different at high speeds, improperly torquing the wheels can warp the rotors,

the gradual humming sound could possibly be a wheel bearing.

 

^ I second that.
As for the shaking while stopping, does the steering wheel shake a lo? If not it would be the rear brakes.

 

As far as the brakes go you're definitley on the right track with the rotors being warped. I would take them to a shop and have them machined down as a starting point.

And as for the humming noise. It's most likely going to either be a wheel bearing or just tire noise. Turn the car left and right while driving to see if the sound gets worse or goes away. Generally if the sound changes it will be a wheel bearing. If not it may just be an excessively noisy tire.

 

Yep, the steering wheel shakes a ton. I'm pretty set its the rotors, I'll have to get those looked at. Wouldnt it be cheaper just to buy new rotors?

Secondly, the humming doesnt seem to change pitch, but it's sort of hard to experiment with on one lane roads around the area. How much does it usually run to replace the wheel bearings? (I really am a noob with cars)

 

the wheel bearing is easyto do on you own. especially if you have to replace rotors anyways. its a hub assembly so no press is needed. take wheel off take caliper off take rotor off. take axel nut off, push axel thru, remove abs sensor, undo 3 or 4 bolts and take off hub, put on new.

 

The shaking could also be a problem with the steering column. I have the same problem with mine.

 

Even when it occurs solely when you brake? See I just assumed it had to be rotors since it only happened on braking.