I have a 1997 Pontiac Sunfire. When I step on the brakes the back brakes grab way too quick and want to lock up. What could this be?
I have seen drum brakes grab under light braking if there is a fluid leak. In my case, the initial grab transitioned to very poor braking as the brakes heated up.
Did someone recently work on the rear brakes? If they adjusted them too tight, that might cause them to actuate early. Another thought is a problem with the parking brake adjustment that causes the self-adjusters on the rear to over-tighten the brakes when you back up and stop.
The other possibility is that the front brakes are not working so all your foot force is going to actuate the rears. Does the brake pedal feel normal? If you slam on the brake, can you make all four wheels lock up?