Semi-trucks are massive machines. Sometimes they also carry huge amounts of cargo in their trailers.
Have you ever wondered about how they are able to stop all of that weight? Trucks have very impressive braking systems.
In this article, we’re talking about drum brakes in semi-trucks. If you’ve ever wondered about the stopping power on a semi-truck, read on to find out…
Here’s a short summary of why Semi Trucks use Drum Brakes:
Semi-trucks use drum brakes as they are designed for heavy-duty use. They are much cheaper to manufacture and maintain, which saves some costs. They are also much lighter than disc brakes which helps to keep the overall weight of the truck down. Drum brakes are stronger and therefore longer lasting.
What are Drum Brakes in a Semi Truck?
Drum brakes are unique in their design when compared to disc brakes. They are an older design, first appearing in 1902.
These days they’re often only found in heavy-duty vehicles such as semi trucks. Smaller vehicles such as cars and SUVs have moved on to make use of disc brakes.
Brake discs generally have more stopping power than drum brakes. It’s estimated that disc brakes are between 20 and 40 percent more effective in stopping a vehicle.
Drum brakes are cylindrical in their shape, hence the name. However, the difference is that the brake shoes are on the inside of the drum, and they push outward to produce friction.
The friction is used to slow the vehicle down. This is unique to semi-trucks in modern times, and there are several reasons why they have not moved on to brake discs.
Why Do Semi Trucks Use Drum Brakes?
You might be wondering why heavy-duty semi trucks are still using a brake design that is over 100 years old to stop themselves.
There are some very good reasons for semi trucks to use drum brakes as opposed to disc brakes though.
Despite disc brakes having better stopping power, there are some advantages that drum brakes have over them.
The first is that they are cheaper and easier to manufacture. Drum brakes go through a lot of strain, so using the more affordable option is better for business.
Another advantage that drum brakes have over disc brakes is that they are lighter. Surprisingly, the older design is actually not heavier.
In a vehicle that is already extremely heavy, saving as much weight as possible is critical. Drum brakes will help to bring the overall weight of the semi-truck down.
Drum brakes are also stronger. Since trucks are heavy and they put a ton of strain into their brakes, having heavy-duty brakes is essential.
Are Drum Brakes Air Brakes in a Semi Truck?
The drum brakes on a semi-truck make use of compressed air to push the shoes into the drum and cause friction to slow the vehicle down.
The air brakes on a semi truck require an engine-mounted compressor. The compressor shoots out high pressured air into the brake line which activates the brakes.
Air brakes are useful in semi-trucks because they are much stronger than hydraulic brakes. It also makes it easier to connect the brakes on multiple trailers behind the tractor.
The air brake system is also much more reliable than hydraulic brakes, and they can still function even if there is a leak in one of the brake lines.
An air brake system is also significantly cheaper and easier to maintain. Coupled with the drum brakes, you have the most inexpensive combination to maintain for your semi truck’s braking system.
How many Brake Drums do Semi Trucks have?
Semi-trucks are normally heavily loaded. This means they need a ton of stopping power to slow themselves down efficiently.
Semi-trucks have brakes on each axle. The average 18-wheeler has 5 axles, which means it has 10 brakes in total.
However, it depends on how many trailers it is towing. For example, the tractor itself only has two axles, and therefore it has four drum brakes.
Extra brakes are put on the trailers, which are connected to the brake system on the tractor using airlines. All the brakes will then be operated in sync with compressed air.
How do Drum Brakes Work in a Semi Truck?
Drum brakes work differently from disc brakes that we find on our everyday road cars. They are pretty unique in their design too.
Drum brakes are composed of an enclosed cylinder. The name drum brakes come from this design since it resembles a drum.
The brake shoes are found inside the drum. On the other hand, on brake discs, the shoes can be found on the inside of the clamps that hold onto the brake disc.
When the brake pedal is pressed, compressed air is released into the brake lines. The air pushes the brake shoes outward against the drum.
The friction caused by the shoes being pushed against the drum is what slows the vehicle down.
With brake discs, hydraulic pressure is used to clamp the brake shoes onto the disc, which causes friction that slows it down.
Do Semi Trucks use Disc Brakes?
It is extremely rare to find semi-trucks that make use of disc brakes. Disc brakes might have more stopping power, however, they aren’t useful to trucks.
This is because disc brakes require hydraulic pressure. Semi-trucks need to use air brakes to be able to connect the trailer’s brakes and allow them to work.
Semi trucks are also extremely heavy. Disc brakes will only add to the weight they are already burdened with.
Are Disc Brakes better than Drum Brakes on a Semi Truck?
Drum brakes are the better option for semi trucks. There are several reasons for this, despite disc brakes being more powerful.
Firstly, drum brakes are cheaper and easier to manufacture and maintain. This eases some of the strained budgets that semi-trucks are under.
Drum brakes are also capable of handling more strain and can last longer. In a semi-truck, heavy-duty parts are needed, and drum brakes are essential for this.
Are there any Advantages to Drum Brakes?
Despite being based on a much older design, there are several advantages to using drum brakes on a semi-truck.
It’s rare to find drum brakes on modern cars, however, on semi trucks they are still a very common sight.
Drum brakes are used as heavy-duty brakes in the modern automotive industry. They are stronger and more durable than disc brakes.
Drum brakes are also much cheaper to build and to keep maintained. This makes them the better option for semi-trucks that will be driving hundreds of miles.
How often should Drum Brakes be Serviced?
It can be difficult to judge the time between having drum brakes serviced. It is best to measure services in miles.
Generally, it varies how often drum brakes need to be serviced. There are several factors to consider.
If a truck is driving many miles, its brakes will need to be serviced more regularly. However, if those miles are predominantly spent on the highway, the brakes can last longer since they are used less often.
The general number of miles that you should be checking your drum brakes in is every 6000 miles. They might not need to be replaced, but it’s best to keep checking them regularly.
This amount can also vary greatly depending on how the truck is driven. If the driver is smooth and easy on the brakes then they will last longer.
It is best to take the semi truck into a brake expert to have them checked when they have run between the advised number of miles.
Semi truck brakes take a lot of strain because of the amount of weight they need to slow down. This can cause them to wear out quicker.
When should Semi Truck Brake Drums be Replaced?
Drum brakes can give some signals off when they are wearing out. It’s important to look out for these to know when to replace the brakes.
The first signal will be felt by the driver. The brake pedal will begin to feel softer and spongier. The driver will need to push the pedal harder and farther back to stop the truck.
This is the first sign of drum brakes that are wearing out. This is often also accompanied by a grinding or squeaking noise while the brakes are applied.
You can also inspect the drum brakes yourself. You need to take a close look at the brake shoes inside the drum.
When they become too worn, these begin to show cracks. Brake shoes can be replaced easily, and if one is cracked it’s best to have it replaced.
How much do Semi Truck Drum Brakes Cost?
The cost of drum brakes varies depending on where you are. However, generally, it costs between $275 and $400 to have them replaced.
You can save money by replacing the brakes yourself. This will cut out the labor cost involved in the process.
However, it is often recommended to use a mechanic or brake expert to assist you with changing the brakes.
This is because brakes are extremely important, especially on a vehicle as heavy as a semi-truck.
How can you Extend the Life of your Drum Brake in a Semi Truck?
There are several ways that you can save your drum brakes in a semi-truck. Most of it comes down to the way that the truck is driven.
If the driver uses the brake pedal smoothly and slowly when stopping the semi-truck, less strain is put on the drum brakes.
When drum brakes work too hard, they produce a massive amount of heat. The heat can cause the drum to expand, which will make the brakes less effective.
Regularly servicing and replacing the drum brakes and the brake shoes will also help to extend their lifespan.