Many older cars still rely on drum brakes in the rear for stopping. Just like disc brakes, drum brakes also have worn parts that require replacement over time.
Drum brake shoes utilize friction material that pushes against a brake drum to generate enough force to slow or stop a car, creating the force necessary for slowing or stopping. Each brake drum has a minimum thickness specification that should be checked prior to replacing them by a mechanic.
A drum braking system uses brake shoes that press against a rotating drum to slow and stop your vehicle, similar to disc brakes on vehicles, to slow and stop. Over time, they wear out due to friction material deterioration just like disc brake pads do; each shoe also contains wear indicators which emit audible sounds when they come close to being worn out – an audible warning when they contact with their drum counterparts.
When the brake pedal is depressed, hydraulic pressure from the wheel cylinder forces pistons against each of the brake shoes. Each shoe features both leading and trailing shoes; when in its leading shoe position its friction material faces toward the brake drum while its trailing shoe’s friction material faces toward a stationary backing plate of the drum brake assembly.
Return springs and pin or anchors hold the shoes against a backing plate, while shoe-disk combinations generate heat during braking force that generates thermal energy that needs to be dissipated through brake drum and backing plate systems. Once brakes are released, return springs pull back the shoes back to their rest positions for easy retrieval by return springs.
Brake drums typically last 200,000 miles before needing replacement due to regular usage or environmental conditions, such as weather changes. Also included within rear drums is an integrated parking brake which may need servicing at some point during their lifespan.
Due to being less complex than disc braking systems, drum brakes do not perform as effectively at managing heat. This can lead to grab, whereby brake shoes remain stuck to the drum after release of brakes causing loss in efficiency and necessitating special lubricants in order to prevent hard to release brakes from occurring.
Brake linings on drum brakes tend to wear out faster than those found on disc brakes due to constant shoe-on-drum contact, so drivers who frequently commute may need to replace their linings more frequently than those who rarely utilize them; certain forms of driving such as repeated rapid braking could hasten this process further.
Drum brakes employ a brake shoe attached to one or more cylindrical brake cylinders (wheel cylinders). When hydraulic pressure from the master cylinder actuates the brake pedal, this squeezes pistons in each wheel cylinder which then push the shoes against a rotating drum, creating enough frictional force to stop your car.
Brake drums are typically constructed of cast iron or steel and covered in dark colors such as black to reflect heat away and help the brake fluid disperse more freely. As such, they tend to be less vulnerable to corrosion than disc brake drums – however this doesn’t protect it against its natural wear and tear.
As any brake system eventually wears down and requires replacement, so too must its drum. One way to determine when this needs replacing is listening out for any audible noise indicating when brake shoes have reached their wear indicator strip (a strip of friction material which contacts the drum when fully worn shoes reach it).
If you hear this sound, it may be time to replace your brake shoes. While the drum itself shouldn’t require replacement, brake shoes typically only last up to a certain point before needing replacing due to excess friction which causes overheating and premature wear and tear of your brakes.
As a general guideline, brake shoes should be replaced every 30,000 miles or two years depending on your driving habits and vehicle maintenance schedule. Furthermore, it is wise to inspect the brake drums regularly for signs of wear-and-tear as well as taking steps to protect them against road debris damage.
Before undertaking a change of drum brakes, it’s wise to consult your vehicle’s repair manual. Since each car differs in how they disassemble and reassemble their brake assembly, knowing how best to disassemble and reassemble is crucial for successful results. In addition, taking pictures before beginning can serve as a useful reminder for how the assembly should look when completed.
Brake Return Springs
Modern cars typically use disc brakes on the front wheels and drum brakes on the rear wheels. Manufacturers don’t usually set specific replacement intervals for drum brakes, but do recommend having them regularly inspected and replacing as necessary. Many car mechanics include brake inspection as part of regular oil change services for drum brakes requiring removal of drums to access system components.
Hydraulic pressure moves pistons in a wheel cylinder to force brake shoes outward, slowing or stopping the vehicle and reduce wear on their shoes by creating friction against their surface. In turn, these pistons also help prevent wear-and-tear.
Brake shoes feature wear indicators that rubbed against the brake drum to notify of their impending wear-and-tear, alerting you it is time for replacement. Brake pads may also become worn over time and create friction against the drum, though this usually only occurs with hard braking applications.
Your vehicle’s drum brakes feature two springs connected to its hydraulic cylinder that are used to keep brake shoes against the drum when not being applied – these springs are known as return springs and are essential in holding them against it during non-braking conditions. As soon as brakes are applied, however, these return springs pull them back away so they do not directly contact with it again.
Your drum brake assembly features springs with specific alignment relative to the “M”-shaped braking axis created by ears on backing plates of the drum. An angular relationship between engagement legs 25 induces a twisting force upon spring members that keeps brake shoes against drum in their appropriate positions; this prevents sliding downward too far against drum which would contact rotor and wear quickly, and maintains proper positioning of shoes against drum.
Brake Self-Adjusting System
Drum brakes differ from disc brakes by having more parts that wear down over time, necessitating replacement and additional attention and maintenance to remain functional. Their complex assembly requires extra care when running properly – including two pairs of brake shoes which produce force necessary to slow or stop your vehicle; their friction material wears down over time and must be replaced – brake cylinders, return springs, etc. make up this internal assembly that must also be taken care of carefully.
At rest, the self-adjust mechanism keeps the gap between brake shoe linings and the drum within an acceptable range. The mechanism uses two brake shoes with shorter lining segments: one primary shoe is shorter than its counterpart secondary shoe; during braking hydraulic pressure from a master cylinder applies hydraulic force to both wheel cylinder pistons, forcing both primary brake shoes into contact with the drum, then wrapping around anchor pin to push secondary shoes against friction surface of drum.
When the brakes are released, return springs pull away the primary brake shoe from its place on the drum and move up, moving the adjusting lever upwards. This causes it to move closer toward its anchor pin again and tightens up the cable tightening the cable tightening shifting of adjustment wheel which has notches that correspond with distance from brake pedal to heel/toe of primary brake shoe which move plate accordingly thereby altering gap between shoes/drum.
If the self-adjusting mechanism or brakes are out of balance, causing the pedal to feel low or spongy, this indicates that brake shoes are no longer making contact with friction surface of drum properly and need adjusting accordingly. Adjusting can be a complex process involving raising car at jack points while safely supporting frame, crawling underneath for access behind wheels and using special tools to make adjustments on self-adjustment mechanisms.