On a 1992 Pontiac Bonneville, the rear brake adjuster is
not externally accessible. Unlike some older vehicles, the 1992 Bonneville uses a self-adjusting system for the rear brakes. There's no manual adjuster that you can turn with a screwdriver or other tool. If you need to adjust the rear brakes, it's likely due to a problem that requires professional attention. Simply attempting to adjust something that isn't there will be futile.
If you're experiencing issues with your rear brakes (like a parking brake that doesn't hold, or a spongy brake pedal), you should have a mechanic inspect the system to diagnose the problem. The problem is likely not a simple adjustment.
