While people are often told not to try and reinvent the wheel, the same can’t be said for the devices used to stop the wheel: the brakes. While old-fashioned drum brakes have been around, in some form, since the days of the covered wagon, a new-and-improved disc brake system started becoming popular in the late 1960s. That’s when auto manufacturers started adopting this new style of brakes.
Why do 4×4’s have drum brakes? Some off-road, 4×4 vehicles still have drum brakes in their rear wheels as a cost-saving mechanism, as drum brakes are considerably cheaper to produce than disc brakes.
Still, the presence of drum brakes in your rear wheels shouldn’t be cause for alarm. All vehicles made in the 1970s and later will use disc brakes in the front wheels. As the front brakes are responsible for 90 percent of the stopping force, drum brakes in your rear cylinder really aren’t going to make a significant difference in your braking performance.
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Understanding Drum vs. Disc Brakes
To get an understanding of why your 4×4 may still have drum brakes, it is essential to understand the mechanics of how each braking system works.
How Drum Brakes Work
The drum brake gets its name because when fully assembled, it looks like a small bongo drum.
However, the drum brake is actually made of two separate pieces. There is an outer shell that has a metal machine facing on its interior. This outer shell spins with the wheel as your vehicle is in motion.
This outer “drum” component rotates around a backing plate that always stays stationary, even when the wheels are spinning. This backing plate contains a series of components known as “shoes,” and when you step on your brake pedal, these shoes force the backing out against the machine facing of the outer drum, creating the friction necessary to slow your vehicle.
While this is an effective means of slowing your vehicle, the major drawback is that the friction created by the shoes pressing against the machine creates significant heat. The outer drum covering then traps this heat inside the brake system, similarly to how a closed pizza box traps the heat coming off a pizza.
Additional heat is created every time the brake pedal is pressed, and once too much heat is trapped within the drum, the brake shoes begin to fade, and performance deteriorates. Because of this, drum brakes are an inferior option to disc brakes in vehicles that stop and start frequently. For example, race cars altogether abandoned drum brakes as disc systems became available.
How Disc Brakes Work
Disc brakes still use friction to slow the spinning wheel, but they have an open-air format that allows the heat to dissipate, significantly reducing the risk of any fading that may occur as the result of frequent braking.
There are three main components of a disc brake system:
- Rotor – This is the “disc” that spins with the wheel while your vehicle is in motion. Made of metal, it will provide the surface area on which the brake pads will create the necessary friction for stopping. Rotors are often manufactured with small slits or holes to further increase heat dissipation.
- Caliper – This houses the brake pads. It does not move while the wheel is spinning and is mounted with a groove to allow the rotor to spin through it freely when the brakes are not needed.
- Brake Pads – These serve the same function as the “shoes” in the inner backing of the drum brake. When the brake pedal is pressed, the calipers squeeze together, and the brake pads press against the metal surface of the rotor. The harder you press on the pedal, the tighter the calipers squeeze, creating more friction and higher stopping power.
Disc brakes quickly cool between applications, meaning that they rarely fade due to heavy use and have become the preferred braking system for all vehicles.
Why Do Drum Brakes Still Exist in Some Vehicles?
If the benefits of disc brakes are so widely known, then why are there still some drum brakes out there?
Cost—that pretty much sums it up.
The process for making disc brakes is a bit more intricate, and the means for designing a rotor, caliper, and brake pads are more costly and involved than just manufacturing the inner backing and outer shell of a drum brake.
The good news is that all vehicles, even those 4×4’s that use drum brakes in the rear, feature disc brakes in the front. As the purpose of a braking system is to stop forward momentum, roughly 90 percent of the braking burden will fall on the front brakes. When it comes down to offroading, it’s good to know that the better brakes are located in the area of heaviest use.
For normal use, rear brakes generally only function to prevent back end fishtailing. Because of this some manufacturers feel like they can save money without affecting performance by implementing drum brakes on the rear cylinder.
What About Dirt and Debris from Off-Roading?
Some manufacturers, like Toyota and Honda, that continue to use drum brakes in the rear of some 4×4’s argue that it is not a cost-saving technique.
Instead, they claim drum brakes do a better job of preventing dirt and debris from affecting performance. That would make drum brakes preferable for off-roading activities where 4×4’s are likely to be in contact with dirt, mud, and debris.
In theory, there is some merit to this claim. The outer drum-like shell does make it very difficult for dirt and mud to enter a drum brake system. While debris could easily be introduced to the rotors of disc brakes, since the disc is open-air.
The argument falls apart on a couple of points, though:
- The constant spinning of wheels creates a centripetal force that sloughs debris off the rotor almost as soon as it is introduced. So even if you drive through a bog or water crossing, any foreign particles that may affect your disc brakes are quickly shed.
- Drum brakes do an adequate job of keeping debris away from the drum shoes, but water can easily get inside the drum, rendering the drum shoes ineffective, as they slip and slide along the metal facing of the drum. As such, it is dangerous to drive a vehicle that relies on drum brakes through water. They may need time to drain or dry.
While some manufacturers may argue that drum brakes are better for off-road purposes, it really doesn’tt hold any weight. Disc brakes are going to be the better option for all types of driving conditions.
What if My 4×4 Has Drum Brakes?
If your vehicle has drum brakes in the rear, you really shouldn’t worry about it. The disc brakes in the front will do the majority of the work, and the drum brakes in the rear offering added support to prevent fishtailing. So even if the drum brakes fail in the rear, you are still going to have plenty of braking capacity.
Drum brakes are still an effective braking system. They have a long history of successful use in motorized vehicles. Today, almost all vehicles will have disc brakes in the front where 90% of your stopping power is.
The only time you are likely to get in trouble with drum brakes is in conditions of overheating or water saturation. So if you don’t plan on making frequent stops and starts or driving through a bunch of water crossing, drum brakes are going to be fine. Even then, if you have disc brakes on in the front, I wouldn’t worry about water.
That said, if you really do not like the idea of having drum brakes in the rear of your 4×4, then there are several brake conversion kits available that will allow you to switch out your drum brakes for discs.
I’ve seen brake conversions happen in the Overlanding community and it may help stopping when you’re carrying all your gear.