I just bought my 04 Bonneville..what last week..and dummy me didn't take it on the highway.

I've got an intermittent vibration at anything over 50mph, everything is fine at lower speeds. So I though wheel balance. Then the other day I had to hit my brakes on the highway and it felt like the rotors were warped, massive pulsing on the peddle and all kinds of noise. Now I'm thinking rotors and brakes.
The issue is I have no problems at speeds lower than 50mph. I've stomped on the brakes at 45 mph and everything works as it should, no pulling, pulsing, sqeaking, etc. I've had rotor issues on other cars before but the problem occurred at low and high speeds not just high speed.

Obviously I'm going to take it apart to see but is there anything special issue about this car I haven't seen or read about yet? I've already read as many FAQ and troubleshooting articles I could find on the car.

They could be mildly warped. I had the same thing happen before. Around town you couldn't tell, otherwise it was bad.

I'd get your balance rechecked too and see if you can get a roadforce done.

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-Car Guy Carl
"Penelope" - 2003 SLE - 247k Miles
"Sydney" - 2000 Honda S2000 - 98k miles

Get the tires balanced first. I do agree with the roadforce balance, should help you see if a tire is bad, etc.

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Bye Bye:

RIP sandrock

Thanks for the responses, I'm gonna try to get this done this week if I don't get called into work again on my day off...

Just wanted to give an update for those who were interested.

Found out I have 3 tires the same size and 1 a different size. After getting them all balanced the vibration is all but gone. I'm gonna put 4 new tires, and all the same size, on later this year.

My braking issue broke before I could get to it. The caliper locked up on my way to work and that was that... A little smoke coming from the tire kinda gave it away..
1 replaced caliper, 2 new front rotors and pads..