Spongy brakes are generally the result of air, gas or water inside the hydraulic system. Car brakes use a hydraulic fluid that transfers force through high-pressure brake lines. If you’ve got something other than brake fluid inside those lines, the brake fluid is less efficient in transferring force. That leads to a spongy feel at the brake pedal.
The most common causes of this trouble stem from the brake fluid itself. If there’s any water in the brake line, heat from the brakes can vaporize the water, resulting in that spongy feeling. Or in some cases, the brake fluid can actually boil if the brakes get too hot.
The easiest thing to do about spongy brakes is to change the fluid. In most cases, that will get the brakes back to operating normally, unless there’s another problem with the brakes. In general, it is wise to have your brake fluid changed periodically. Besides causing spongy brakes, water in the brake fluid causes corrosion that can ruin calipers and brake cylinders. Brake fluid changes are relatively cheap, so you should have it done every year or two. That’s all part of proper maintenance for your car, as covered in Top 10 Car Care Tips.
Many older vehicles use drum brakes on all four wheels, or just the rear wheels. The drum brake uses brake shoes instead of brake pads to slow or stop the vehicle, and have been replaced on most modern passenger vehicles by the disc brake system.
A brake drum is shaped like a bowl, and brake shoes are installed inside the drum. When the brake pedal is pressed, the wheel cylinder presses the brake shoes outward, against the sides of the drum to create braking force. The brake drum is indirectly attached to the wheel, so when the brake shoes are forced against it, the wheel must stop as well.
Customers with drum brake systems often specify they have lost braking power, or that the vehicle's brakes are making noise. This is because brake drums do not dissipate heat very well, so the heat from hard braking will cause stress fractures. These fractures make can make noise on the brake shoes as the drum revolves around the shoes. Lastly, the brake shoes may not be problematic, but may cause a grinding noise while stopping. This would indicate the shoes have no braking material left, and the brake shoes must be changed before the vehicle can be safely driven. Learn more about brake shoe symptoms
It is not safe to operate any vehicle with any braking problem. If there is any sign that the brakes are not performing as originally intended, the vehicle should immediately be placed out of service, and repaired. If the brakes are being replaced as part of routine maintenance, with no symptoms noticed, the vehicle can be safely driven to a repair shop.
Brake shoes are typically replaced as part of a standard brake service, so the average serviceable lifespan depends on driving style, and operating conditions. The manufacturer recommended maintenance schedule for each vehicle may be different, and the owner's manual will contain this information. The brake shoes are considered “normal wear and tear” items, and are understood to require replacement multiple times within the useful life of a vehicle.
Diagnosis for brake shoe replacement requires removal of the wheel and brake drum, and physically inspecting the brakes. If the brake shoes have passed their wear limit, or show signs of uneven wear, replacement will be recommended.
The brake shoes must be unadjusted to be released from the brake drum. Then, the wheel must be removed, and then the drum can slide off the wheel lug studs and brake shoes. Once the drum is removed, several retaining springs and clips must be removed to free the brake shoes from the backing plate. All springs and clips must be replaced with new hardware, and the replacement drum is installed by sliding onto the wheel studs and brake shoes. The brake shoes can be readjusted before the vehicle is placed on the ground.
When replacing brakes of any kind, it is important to replace the corresponding brakes on the other side of the vehicle. This will ensure braking power is even and predictable.
Brake drums are notorious for being difficult to remove after a long period without regular service. To remove the brake drum in this situation, the brake shoes must be completely unadjusted, and the drum pried off, hammered off, or a combination of the two. Regular cleaning and adjustment services should be performed on all drum brake systems to ensure proper function, and estimate remaining service life of the brake shoes. New brake shoes should be installed anytime the brake drum is machined or replaced. Likewise, the brake drum should be machined or replaced any time new brake shoes are installed. Failure to replace these as a set will result in unpredictable braking performance, lack of stopping power, and brake noise.
The braking system can be maintained by a DIYer with a complete knowledge of hydraulically actuated systems. This is important as testing brake operation, and safe installation of braking components rely on this knowledge. If the complete braking system is not understood, damage to the expensive braking components, or injury is likely. Trusting a professional technician with the replacement of any braking component is normally the best course of action.