A brake drum is basically a shallow cast-iron cylinder. The inside drum of the cylinder is a machined surface that the brake shoes press against when applied. Most of the reasons for replacing a brake drum have to do with the condition of that drum surface; each time the brakes are applied, they create friction and heat and wear the drum a little bit. Over time, a brake drum can become out of round or it can wear to an excessively large diameter. Rear brake shoes and brake drums wear very slowly, as compared to disc brakes, but if a brake shoe wears down to the metal, or if an emergency brake is left applied, a brake drum can be easily damaged.
Usually, during a brake job, the drum is removed and machined to provide a smooth inner surface for the new brakes to work against. They are also measured across the inside diameter to make sure they are still usable; there is a specification for the maximum inside diameter, and if a drum can’t be machined within that spec, it needs to be replaced.
Drum brakes were once the main type of brake system used, both front and rear. Disc brakes have the advantage of being more responsive as well as running cooler, so almost all vehicles since the early 70’s have used disc brakes in the front, which does the most work. When ABS brakes became the norm, drum brakes again declined in use, as they don’t respond as rapidly and don’t work as well in an ABS system.
But there are still many light trucks and economy cars that use rear drum brakes.
Cost of Brake Drum Replacement
In the great majority of cases, replacing a brake drum will occur in conjunction with a brake job. Then the cost will be for the part only, as no extra labour is involved. On average, a brake drum on a passenger car costs about £30. On average, a brake drum for a light truck costs about £60.
If a brake drum is replaced separately from a brake job, it will usually be done in conjunction with a brake adjustment, and be charged out at about an hour of labour. The average cost of replacing brake drums on a passenger vehicle would then be about £150, and for a light truck, it would be about £230.
For some specific examples of common vehicles, using £70 an hour as a labour rate:
For a 2008 Toyota Tacoma, replacing the rear brake drums and adjusting the brakes takes about an hour of labour. A factory brake drum costs about £119, and a non-OE drum costs about £55. That makes the job about £190 using OE parts, or about £125 using aftermarket parts.
For a 2006 Kia Spectra, the labour to replace the rear drums and adjust the brakes is about an hour. A factory drum costs about £70, and a non-factory drum costs about £23. That makes the job of replacing the rear drums about £140 using OE parts or about £93 using aftermarket parts.
For a 2008 Chevrolet Cobalt, replacing the rear drums and adjusting the brakes takes about an hour of labour. A factory rear drum costs about £147, or a non-OE drum costs about £26. That makes the job about £217 using OE parts, or about £96 using aftermarket parts.
How to Tell if You Might Need Brake Drums
The main indicators would have to do with how the brakes work. If there is squeaking or grinding, or if the brakes grab too hard or don’t grab hard enough, then the brakes would be inspected and measured to see if new rear drums are needed. Other symptoms might be shaking when the brake is applied, indicating the drums could be out of round. If the emergency brake doesn’t hold well, that can indicate the brakes are out of adjustment, or that they are worn out, or that the drums are worn past specification. Most of the time, an ordinary brake inspection would determine the problem.
No, rust on the outside of the drum is unavoidable, unless it’s specially coated (which is rare); rust on the outside doesn’t hurt anything. Drum brakes are usually shielded to keep moisture out of the inside, except in cases of submersion. Even then, usually the brakes dry out OK and no harm is done.
They have to be measured across their inside diameter. The specs for maximum size are usually stamped into the drum, and they should be measured with an inside calliper that goes down to a thousandth of an inch. A measuring tool would be available at machine shops and many parts stores.
Almost the life of a vehicle, unless damaged by a failed component or having brake shoes run down to the metal. They wear very slowly as compared to brake rotors.