Manager Forum

We have a 2007 Chevy Malibu LTZ w/o stability control, the brakes will apply on their own without the pedal being pushed.

The pads, calipers, and rotors were shot so we replaced them. After doing so, we drove it for 10 miles no issues. Customer picked the vehicle up and it did it again. Put the car on the hoist and let idle and after some time we couldn't turn the left front and right rear, pulled the vacuum hose on the booster and it released. Installed a booster and still does it.

Looking for some ideas.

I have seen a master cylinder do this. Not saying that's what's wrong but I have seen it. I have also seen a brake hose do this but the fact it's doing it at 2 wheels the master cylinder seems more likely than a hose.

In theory, a booster would not act on only one channel of the brakes. I'd go with a master cyl.

Master cylinder would do this but before I started tossing more at it I would want a complete history. Have you been exclusively working on this or has it been somewhere else? If the customer had been complaining about a low pedal at another shop and they thought of "adjusting" the booster push rod that could be your issue. I think something mechanical is applying pressure to pedal just enough to slowly activate the booster. I don't want to sound like the Farmers Insurance Ad but been there, seen it, fought through it. I was there (long long time ago) I would spend time looking for any "technical issues" caused by a technician. These are the most difficult to find but it does sound like a rod adjustment or pedal being held down issue. Good Luck.