A brake drum is basically a shallow cast-iron cylinder. The inside drum of the cylinder has a machined surface that the brake shoes press against when applied. Most of the reasons to replace a brake drum have to do with the condition of the 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 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 used to be the main type of automotive brake system, 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 1970s use 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 labor is involved. A brake drum on a passenger car costs, on average, about $40. A brake drum for a light truck costs, on average, about $120.
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 labor. The average cost to replace brake drums on a passenger vehicle would then be about $250, and for a light truck, it would be about $400.
For some specific examples on common vehicles, using $150 an hour as a labor rate:
For a 2008 Toyota Tacoma, replacing the rear brake drums and adjusting the brakes takes about an hour of labor. A factory brake drum costs about $127, and a Wagner premium drum costs about $120. That makes the job about $404 using OE parts, or about $390 using aftermarket parts.
For a 2006 Kia Spectra, the labor to replace the rear drums and adjust the brakes is about an hour. A factory drum costs about $80, and a Raybestos drum costs about $54. That makes the job to replace the rear drums about $310 using OE parts, or about $254 using aftermarket parts.
For a 2008 Chevrolet Cobalt, replacing the rear drums and adjusting the brakes takes about an hour of labor. A factory rear drum costs about $157, and a Bendix drum costs about $60. That makes the job about $464 using OE parts, or about $270 using aftermarket parts.
How to Tell if You Might Need Brake Drums
The main indicator 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 were needed. Other symptoms might be shaking when the brake is applied, indicating the drums could be out of round. Of course, the front disc brakes do most of the work, wear fastest, and are more likely to be a source of any of the above problems, but any brake check looks at both front and rear. If the emergency brake doesn’t hold well, that can indicate the brakes are out of adjustment, that the shoes 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 okay, 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 caliper that goes down to thousandths of an inch. Machine shops and many parts stores would have a measuring tool.
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.
Yes, drums are almost always replaced in pairs, in order to keep the braking forces equal and even on both wheels
No, unless they need it based on wear or condition. Rear drum brakes usually last two or three times as long as front disc brakes, at least.
Taking it easy on the brakes is the normal advice; brakes wear depending on how hard they are used. Not driving with the e-brake on is basic. One bit of advice that used to be common was to not apply the e-brake after the vehicle had been driven hard, as the pressure could warp hot brake drums. Whether that’s something to actually worry about or not, this writer is not sure.