Troubleshooting car problems of partly on brakes while braking
There are two possible cause of this kind of problem and to determine what causing it is to do the auto diagnose.
1) Inspect your car brake pedal. Check all around the pedal if there is anything that is restricting the brake pedal to move normally.
2) Try to depress the brake pedal and observed if it moves freely without any resistance from the initial travel of approximately 1 to 2 inches then it will start to have resistance as the brake is engaging.
3) If the brake is operating normally then the problem is that your car brake pedal has an incomplete retraction which causes the brake to drag. When the brake pedal is not fully retracting, it will stay down and thus the brake is always engaged.
4) However, if the brake pedal is operating normally but all of the brakes are partly engaged then a possible causes a problem on the brake master cylinder. Master cylinder provides hydraulic pressure that activates all your car bakes if the master cylinder has a problem it will not completely letting up on the hydraulic pressure thus causing the brakes to still partly engage.
Possible Cause of Problem
Incomplete retraction of brake pedal or Problem with the brake master cylinder.
How to fix brakes that partly on while braking
In any case, bring your car to a reputable auto repair shop that specialized with brake system and have a mechanic to inspect the car. Have the mechanic to check if the master cylinder push rod is out of adjustment, it has a swollen primary piston cup, or a blocked bypass port. Have this problem taken care at once to avoid a more serious accident that may arise in the future.