Front drum brakes, or any brakes, pull to one side because there is something wrong with the brakes on one side of the car, and the good brakes pull the car in their direction.
Front drum brakes can pull to one size because the caliper piston or caliper slides are seizing up. If this happens on one side, the brakes on the good side will pull the car in that direction. In this case, you need to replace the caliper piston and brake pads. It's also possible that you have a blockage in the brake line leading to one of your calipers in front.
If brake fluid leaks from your master cylinder, it will cause a loss of friction in the brake shoes. This problem can progress if uncorrected with air being drawn into the master cylinder, which will also cause the brake pedal to become soft. Get the leaky seal fixed as soon as possible.
Front drum brakes can also pull to one side because there is oil or grease on one of the brake pads, or because wheel bearings are loose. Front brake pull can even be caused by different types or thicknesses of brake pads on either side of you car. All brake pulling problems should be inspected and fixed immediately.
