Drum Brakes’ Main Disadvantage: Heat-Induced Brake Fade

The main disadvantage of drum brakes is their susceptibility to heat-related brake fade during repeated or sustained braking, because the enclosed drum traps heat and gases, reducing friction and stopping power. While drum brakes remain common on the rear axles of many budget cars and some EVs, their thermal limitations make them less consistent than disc brakes under heavy use.

How Drum Brakes Work

Drum brakes use a circular drum attached to the wheel and a set of brake shoes that press outward against the drum’s inner surface to create friction. Hydraulic pressure from the wheel cylinder pushes the shoes outward; return springs retract them when the pedal is released. A design trait called “self-energizing” means the rotation of the drum can pull the leading shoe into tighter contact, boosting braking force with less pedal effort—but also concentrating heat in specific areas.

Why They Fade Under Heat

All brakes convert kinetic energy into heat, but drum assemblies shed heat poorly. The friction surfaces sit inside a closed drum with limited airflow, so temperature rises quickly under repeated stops or long descents. As temperatures climb, the friction coefficient of the lining can drop, the drum expands away from the shoes, gases and dust can accumulate, and the driver experiences a noticeable loss of braking effectiveness.

The following points outline the main technical reasons drum brakes are prone to fade under demanding conditions.

• Enclosed design: The drum traps heat and outgassed resins, limiting cooling and allowing a boundary layer that reduces friction.
• Thermal expansion: The drum grows with heat, increasing the shoe-to-drum clearance and pedal travel, which can reduce effective contact pressure.
• Self-energizing hotspots: The leading shoe can overwork and overheat, creating localized fade and glazing of the lining.
• Gas and dust buildup: Outgassing and wear debris can temporarily “lubricate” the interface, lowering friction until conditions cool or clear.
• Wet performance lag: Water can be slow to evacuate from inside the drum, initially reducing friction before heat dries the surfaces.

Taken together, these factors mean that even if initial stops feel strong, sustained braking pushes drums past their thermal comfort zone faster than discs, leading to inconsistent and lengthening stopping distances.

What Drivers Notice

In real-world driving, drum brake fade tends to appear progressively as temperatures rise during repeated or prolonged braking, especially on steep downhill grades or when towing.

1. Longer stopping distances despite steady or increasing pedal effort.
2. Pedal feel changes—either more travel (due to drum expansion) or a firmer pedal with less effect.
3. Odor or smoke from overheated linings; possible wheel-end discoloration.
4. Initial “grabby” response followed by rapid fade as heat builds.

These symptoms are warnings that the brakes are outside their optimal operating range and need time to cool before they regain consistent performance.

How Disc Brakes Compare

Disc brakes expose the rotor to open airflow, which sheds heat far more effectively. Their pad-rotor interface is self-cleaning, less prone to gas buildup, and maintains a more stable friction coefficient at elevated temperatures. This is why most modern vehicles use discs on the front axle, where braking loads are highest. Drums still appeal for rear axles on cost-sensitive models and some EVs—where regenerative braking reduces friction-brake workload—and for integrated parking-brake mechanisms and corrosion resistance in salted climates.

Mitigations and Use Cases

Manufacturers can improve drum performance with finned drums, larger diameters, better friction materials, and proper adjustment mechanisms. For typical urban and suburban driving, especially with lighter loads, rear drum brakes can perform adequately and economically. However, for frequent mountain driving, towing, spirited driving, or repeated high-speed stops, disc brakes offer superior heat management and consistency.

Summary

The principal drawback of drum brakes is heat-induced fade: their enclosed design traps heat and gases, causing a drop in friction and longer stopping distances under repeated or sustained braking. While drums can be cost-effective and adequate for lighter-duty rear applications—particularly when supplemented by regenerative braking—discs remain the preferred choice where consistent, high-thermal-load performance is required.

Why did we stop using drum brakes?

Drum brakes are not used on most cars anymore because disc brakes offer better cooling, shorter stopping distances, and more consistent performance, especially under heavy use or in wet conditions. The enclosed design of drum brakes traps heat, leading to brake fade (reduced effectiveness), and can be more complicated to service and are less efficient than modern disc brake systems. However, their ability to dissipate heat less efficiently and their tendency to lose effectiveness in wet conditions made them unsuitable for the increased demands of modern driving and highway speeds.
 
This video explains why disc brakes are better than drum brakes: 15sSummit RacingYouTube · Apr 12, 2021
Key Reasons Drum Brakes Are Less Used:

• Overheating and Brake Fade The enclosed design of drum brakes prevents heat from escaping, leading to overheating and brake fade during heavy or sustained braking, which significantly reduces stopping power. 
• Poor Performance in Wet Conditions Water and moisture can become trapped inside the drum, severely impacting the brakes’ performance until they dry out. 
• Longer Stopping Distances Disc brakes generally provide shorter stopping distances compared to drum brakes, a crucial safety factor for modern vehicles and highway speeds. 
• Complex and Less Efficient Servicing Drum brakes have a more complex design with numerous parts, making them more difficult to service than disc brakes. 
• Outdated Technology for High Demands The technology behind drum brakes wasn’t designed for the high speeds and frequent hard braking of modern cars. 

Why Disc Brakes Are Preferred:

• Better Heat Dissipation: The open design of disc brakes allows heat to escape more efficiently, preventing brake fade and maintaining consistent performance. 
• Self-Adjusting Capabilities: Disc brakes offer a more self-adjusting design, ensuring more consistent braking. 
• Improved Performance in Wet Conditions: They perform more reliably in wet weather than drum brakes. 

Where Drum Brakes Are Still Used:
Despite their drawbacks, drum brakes still have niche applications, such as for the parking brake on some modern vehicles. They are also used in certain types of long-haul trucks where the operational conditions and braking demands are different from those of a standard car. 
Note: For electric vehicles, there is some discussion of a comeback for drum brakes due to their benefits in low-usage, low-dust environments.

Can I spray WD-40 on drum brakes?

But for metal clutch components as well the powerful cleaner will rinse off grease oil brake dust brake fluid or oily handprints. And all manner of contaminants.

What is the greatest disadvantage of drum brakes?

Cons. Overheating – One of the biggest downsides to drum brakes is their tendency to overheat quickly in conditions where a driver has to brake frequently. This occurs because the components are housed within the metal drum with limited air circulation.

Which is safer, drum or disc brakes?

Safety First: Regardless of cost considerations, safety should always be your priority. The superior stopping power of disc brakes can make a significant difference in emergency situations, potentially outweighing any cost savings from choosing drum brakes.