My wife has been driving to work her '99 Bonneville SE.
She told me today that when she occassionaly has to brake hard (say coming down from fifty to sixty miles per hour when the freeway backs up) the Bonneville shimmy'* and shudders.
Anybody have an idea on what may be wrong here?
**front brake pads look fine, brake fluid is also fine.

Depends on how hard she'* clamping the binders. Could it be ABS? They'll feel like they're pulsing. Try pulling the ABS fuse and see if the problem goes away. On my 93, the fuse (BIG one) is under the hood in the relay center just forward of the passenger.

Jr,
This '99 has 44K miles.
We just recently bought the car.
The brake pads look new however maybe the dealer where we bought the car installed new pads without first treating the rotors, turning them?
Do you think that could be the problem?
Driving-wise my wife is just doing a standard 40 mile freeway commute.
Occassionally traffic backs up to a standstill or slow crawl and drivers need to shut it down quickly from 60 mph to prepare for a stop.
This happens, car should not shudder and shimmy.
My '96 Caprice, a heavy,, full-size sedan, does not do this.
We got a 3,000K-3-month GM warranty on this car and I am fishing here for some possible guidance to give a dealer.
Thanks for your help.

Jr.,
I went ahead and ordered some brand new rotors and pads.
My guess is the dealer (where we bought the car) had taken it in trade, put on some new pads without turning the rotors.
At 45K miles brand new ones are not a bad idea so that'* what I am going to do.
I doubt a GM dealer would cover this under the warranty however when my local mechanic does the tune-up and rotor installation next week I am going to have him look for possible problems that my be covered under the dealer warranty.
Thanks for your input here.

I have a 99 Bonneville SE with 95k miles now. I had the same problem, I fixed it by buying Powerslot rotors which have not warped even from me going from 105 to 0 stops and me cooling them off with water. They are a worthwhile buy. I think the stock OEM dics have a tendency to warp more but they are cheaper. Just depends on your application.

99,
I paid $100 per rotor for stock GM.
Is that a reasonable price?

I paid $200 shipped for my Powerslot slotted rotors.

$200 each? :?:

Uh... no.. a pair of slotted rotors from Powerslot for $200 shipped. IF each rotor cost $200 , noone would really buy it, would you?