I have been having some trouble with my car lately. Its a 2005 chevy cobalt ss which has the 2.0l ecotec supercharged engine. I did a brake job about two weeks ago because the car had 60xxx miles and I wasn't sure if they had been replaced or not. The car seemed like it wasnt braking as well as it used to and it was squeaking so I figured I needed to replace them. I replaced the brake pads and rotors, I wire brushed the calipers and brakets and I lubed the slides as well. Exactly one week after the brake job I have been having what I think are brake problems. Now before I describe this I want to say that this problem only occurs at freeway speed while IM NOT applying the brake. What happens is I will be cruising along at about 80mph and my car will suddenly begin to slow down. I literally have tried flooring the gas in a lower gear (I have a manual) and I still cant make it accelerate. My gas mileage goes from about 28mpg to 9mpg. When I pull off the road my car will stop suddenly as if the brakes are applied. I can smell burning brakes however its usually windy and I cant tell from touch or smell where the heat or smell is coming from. Once get it off the highway it drives fine. I have also noticed that when the car starts to slow down to brake pedal gets rock hard however the performance of the brakes are not affected, they stop the car just as good as they usually do except I just dont have to push the pedal as far. If I pump the brakes a few times the pedal seems to soften up and I get my acceleration and normal mpg rating back.

With that being said here is what I have done so far
-I put the car on jack stands to spin the wheels to check for resistence. All wheels spin the same but like I said this problem only occurs at about 70+mph

- I tested the booster by pumping the braked with the car off until they are hard. When I start the car the pedal softens right up again.

-I tried bleeding the system but the bleeder broke off in the hole so I gave up on that shortly after

-I removed the wheels and calipers to insure the calipers turned in easily and there were no obstructions for the brakes to return. Everything seemed to be in order.

-I removed my fuses for the abs module this morning. The pedal got a little stiff on the freeway but the car didnt slow down, however this problem doesnt happen all of the time so I have not driven the car long enough to say the problem has gone away.

-if it was a caliper sticking wouldnt this problem occur only when pressing the brakes? when this problem happens to me I honestly havent touched the brakes for about 5-10 minutes.

-I have toyed with the idea of brake fluid contamination because when I added brake fluid I over filled it and used a suction gun to remove the excess. The suction gun was used last year to remove rear end lube from my other car but my dad said he thouroughly cleaned it and if any got in there it would have been so tiny it shouldnt hurt anything.

So at this point im spent on ideas and I have been searching forums like crazy for people with similar issues but have not had luck thus far. Does anyone have any ideas or knowledge on this issue? I would appreciate any input on this and I thank you for your time.

 

I haven't had tis specific problem, however, when I bought my car (at 84000 miles) the dealer said that the brakes were brand new. whenever I got to highway speeds, they would violently rub like the rotor was out of round. Long story short, the new rotors that were put on don't fit as snug as I feel they should, usually it takes a little effort to get a rotor on, and these seem to go on with a gap. My problem was fixed by making sure the rotor was pushed on all the way, and tried not to hit it with the wheel when I installed it until I tightened the lug nuts. I hope this helps some, even though it was a different problem, it's something to check.