If the brake rotors had any detectable ridging on them they need to be turned or replaced. That ridging will cause the pads to migrate a little so as to possibly cause a slight angular misalignment of the pad to rotor as the pad adheres to the rotors form of ridges. Will cause a pulling to left or right and excessive brake pad wear along with less braking grip. Bedding the brakes could help, but all those issues will pop up if that is is the case of a rotor in need of service. If the rotor is out of true (warped), you might also have similar issues.
If the rotor is not an issue the next place to look is bleeding of the brake fluid. Brake fluid will 'absorb' water over time and become less efficient. Always use a new unopened (seal not broken) brake fluid can to bleed the brakes. Preferably you would do this to all four brakes in one session as it is plausible that the low pad condition was allowing air into the brake lines.
Speaking of air in brake lines, all four of the flexible rubber hoses near the brake assembly could also be deteriorated, micro pin holes allowing air into brake system lines, if they have not been replaced in the last 4-6 years. On occasion the bleeder valve could also be problematic if ball bearing in it is stuck slightly open (or rusted so as to cause it to crack open from running in water).
Driving on the beach or through water (street flooding, or creeks) can also cause brake performance issues after a period of time. Particularly brake line corrosion and brake components getting stuck.
If all the above is replaced and or check out as good, then it would likely be the brake master cylinder, the brake vacuum booster or the hose or check valve to the manifold failing. However if brakes worked good (did not go halfway down) prior to the pad swap, these things are less likely- unless you have done other work in that area of the engine compartment.
Additional Brake info:
The Rear brake parking break should be reset every once in a while by driving > 20 mph in reverse, then stopping hard several times. If pads and components were replaced here, and that does not improve the parking hold, then the parking brake lever needs to be adjusted, if still not holding, then the parking brake cable is known to stretch over time and may need replacing also.
If the rotor is not an issue the next place to look is bleeding of the brake fluid. Brake fluid will 'absorb' water over time and become less efficient. Always use a new unopened (seal not broken) brake fluid can to bleed the brakes. Preferably you would do this to all four brakes in one session as it is plausible that the low pad condition was allowing air into the brake lines.
Speaking of air in brake lines, all four of the flexible rubber hoses near the brake assembly could also be deteriorated, micro pin holes allowing air into brake system lines, if they have not been replaced in the last 4-6 years. On occasion the bleeder valve could also be problematic if ball bearing in it is stuck slightly open (or rusted so as to cause it to crack open from running in water).
Driving on the beach or through water (street flooding, or creeks) can also cause brake performance issues after a period of time. Particularly brake line corrosion and brake components getting stuck.
If all the above is replaced and or check out as good, then it would likely be the brake master cylinder, the brake vacuum booster or the hose or check valve to the manifold failing. However if brakes worked good (did not go halfway down) prior to the pad swap, these things are less likely- unless you have done other work in that area of the engine compartment.
Additional Brake info:
The Rear brake parking break should be reset every once in a while by driving > 20 mph in reverse, then stopping hard several times. If pads and components were replaced here, and that does not improve the parking hold, then the parking brake lever needs to be adjusted, if still not holding, then the parking brake cable is known to stretch over time and may need replacing also.
