What Causes Drum Brake Lock-Up?

[Leonard]

The reasons for drum brake lock-up are as follows: Brake Caliper Not Retracting: Even when the brake pedal is not pressed, there is a noticeable resistance felt in the vehicle. In severe cases, abnormal noises may occur, or the wheel may even lock up. If the brake fluid has not been replaced for a long time, causing internal corrosion of the brake caliper, it can be repaired by sanding and applying grease. If the caliper itself is faulty, it may need to be replaced directly. Brake Master Cylinder Cup Jamming: This is usually caused by water or other contaminants entering the brake system, or failure to clean the system before switching to a different brand of brake fluid, leading to swelling of the brake master cylinder cup and causing lock-up. This issue is not a design flaw but rather a result of incorrect operation. The solution is to clean the entire brake system and replace the brake master cylinder cup.

[LeRuth]

I remember back in the day when dealing with drum brake lock-up on vehicles, the most common cause was uneven wear on the brake shoes, leading to uneven pressure during braking and causing them to jam. Another frequent issue was out-of-round brake drums, often caused by high temperatures or vibrations—like from frequent braking in city driving over time, which can make the drums lose their roundness and cause sticking. Problems with the hydraulic system aren’t uncommon either, such as rusted pistons or contaminated brake fluid preventing the shoes from retracting properly. A broken or weakened return spring can also fail to pull the shoes back into place. Additionally, if you drive through water and don’t dry the brakes by driving a bit afterward, moisture can accumulate inside the drum and cause the shoes to stick. It’s recommended to inspect them every six months, resurface the drums or replace the shoes, and avoid cheap, low-quality parts—otherwise, a locked-up wheel can be extremely dangerous. These issues are more common on older cars, and neglecting them can damage the wheel hubs over time.