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When To Replace Semi Truck Brake Drums? (Explained & Solved)

The brakes on a semi-truck take a lot of strain due to the amount of weight and momentum that needs to be stopped.

It can be difficult to judge when your brakes need to be replaced. If there’s anything you need to know about worn-out brakes, read on to find out.

Here’s a quick answer to When to Replace Semi Truck Brake Drums:

Semi-truck brake drums usually last 100,000 miles on average; however, it often depends on how they are used, and they might go longer or shorter. It would help if you replaced them when the brake pedal goes soft or begins to vibrate when you press the pedal down.

How Long do Semi Truck Brake Drums Last?

The answers to how long the drum brakes on a semi-truck last vary a lot. There are several factors that influence how long the brakes will last.

Some brakes will only last 70,000 miles. On the other hand, drivers have reported their brakes to last as much as 250,000 miles.

The range between these two is massive, so it can be difficult to judge how long the drum brakes will last on your semi-truck.

A good ballpark for the mileage on the drum brakes is around 120,000 miles. However, it all depends on how the semi-truck is driven.

If the driver uses the brakes often or brakes hard, then the brakes will wear out faster. Maintenance is also crucial to keeping your brake drums’ lifespan as long as possible.

When to Replace Semi Truck Brake Drums?

It can be difficult to judge when you need to replace the brake drums on your semi-truck. However, there are a few important things to look out for.

The best way to determine if the brake drums need to be replaced is by doing a visual inspection. You can do this yourself or send the semi-truck to a mechanic.

The brake drums should be replaced if there are visible cracks on them. We will cover this in further detail later on.

You can also measure the inner diameter of the drum. If the brake surface diameter exceeds the allowable limits, the drum must be replaced. The diameter should not exceed.

120 inches over the original diameter.

A good idea is to also check the heat distribution on the brakes. You can do this by analyzing the discoloring on the brake drum.

Normal heat discoloring will show up on the surface of the drum, but you need to look for heat discoloring that is focused in one area or not evenly distributed.

This can show that the brake drum has a specific weak point when it becomes too hot. Over time this could lead to cracks and fractures.

What are the Signs of a Bad Semi Truck Brake Drum?

When your brakes begin to wear out, the brake pedal will begin to feel inconsistent. The pedal might have a lot of pressure sometimes, and other times it might have less pressure.

Another sign that you need to get your brakes checked or even replaced is if you can hear a metallic scraping sound while braking.

You might also feel that you need to press the brakes harder than usual to get your semi-truck to slow down. This could be down to worn-out brake drums.

In some cases, you might feel vibrations through the brake pedal, or in some more severe cases, you will feel vibrations through the steering wheel of your semi-truck while braking.

Semi Truck Brake Drum Wear Limit

All brake drums have a wear limit. This is the maximum allowed amount of wear on the brake drum. Any wear beyond this point is deemed to be unsafe and would be illegal.

All brake drums will have the wear limit engraved on the outer surface of the brake drum. To measure the wear, you need to measure the diameter of the inside of the brake drum.

This is because brake drums wear from the inside. Brake drums work by pushing the brake shoes outward against the inside of the drum.

The majority of brake drums have a wear limit of 16.620 inches. A new brake drum has a diameter of 16.5 inches.

How do You Measure The Wear of a Semi Truck Brake Drum?

If you take your semi-truck into a workshop, they will use complex and expensive tools like a drum micrometer to measure the inner diameter of the brake drum.

This will give them an extremely accurate representation of how worn out your brake drums are; however, they can sometimes charge a lot for this process.

You could also do it yourself, even if you don’t have the expensive equipment. The first step is to remove the brake disc from your semi-truck.

You can then take a few pieces of wood or PVC and cut one piece at the maximum diameter, which is 16.620 inches, and cut another piece at the halfway worn point, which would be 16.560 inches.

By placing these inside the drum, you can quickly tell approximately how worn your drum is. Be sure to place them straight and not at an angle.

How Can You Tell if a Brake Drum is Out of Round?

Out of round drums have different measurements at different points in their diameter. In other words, they are not perfectly circular.

While no drum is likely to be a completely perfect circle, they should not be excessively out of round. This can cause severe braking problems.

Brake drums can go out of round when they become too hot due to being used too often or too aggressively.

They can also be out of round if they are not stored correctly or are not handled with care. They can easily be damaged if they are dropped, for example.

You can check if a brake drum is out of round by using the same technique as above.

Using the PVC pipe that has been cut to the right length, you can spin it around to ensure that all areas are the same measurement.

Brake Drum Cracks CDL

The CDL or commercial driver’s license has several requirements that you need to know. One of these is the cracks on brake drums.

This is because cracked brake drums can be extremely dangerous. If the cracks are too large, it could fracture the entire brake drum resulting in a loss of stopping power.

Brake Drums Must Not Have Cracks Longer Than

“Brake drums or discs must not have cracks longer than one-half the width of the friction area.”

It is unsafe to drive if any vehicle with a brake drum has a crack more than one-half of the width of the friction area.

Should Brake Drums Have Grooves?

Brake drums should be smooth without any grooves on the inside. The grooves can cause excessive wear to the shoes and the drum itself, which will reduce the performance and lifespan of the brakes.

It is often caused by a foreign object that has been caught in the drum or a broken brake shoe inside the drum.

Can You Drive With a Bad Semi Truck Brake Drum?

Technically you can drive with a bad brake drum. However, it is not recommended. You should have it replaced as soon as you can.

When driving with bad brakes, it is important to drive with extra care as you do not want to put more strain on the already fragile brakes.

In the majority of cases, it is not worth driving with bad brake drums. It is always best to replace them before they start giving your problems.

Can You Repair a Bad Semi Truck Brake Drum?

In the majority of cases, it is best to replace the entire brake drum. It is difficult to repair brake drums, especially since they are built for heavy-duty operation.

A brake drum that is too out of round, too worn, or is rough on the inner diameter is better off being replaced.

The effort to refurbish a brake drum is not worth the trouble when you can easily have it replaced.

How Can You Prolong the Life of a Semi Truck Brake Drum?

There are several ways that you can extend the lifespan of the brake drums on your semi-truck. These may seem obvious. However, they are often overlooked.

The first is not to drive too fast. The faster you drive, the more often you need to use your brakes. If the brakes are used too much, they begin to wear out faster.

It would help if you also avoided braking sharply. Sharp and hard braking will put more heat and stress into the brakes, which can take time off their lifespan.

Regular maintenance is also great for extending the mileage on your brake drums. You should inspect the brake shoes regularly, as they can cause damage to the drums when they begin to wear out.

Brake shoes have a metal plate beneath their friction pads. When the friction pads are worn out, you will have metal scraping against metal inside the brake drum. It’s an easy way to ruin your brake drums quickly.

How Much does it Cost to Replace a Semi Truck Brake Drum?

Brake drums can vary in price depending on the type and the manufacturer that you choose from. Standard and lower-quality drums are cheaper than heavy-duty drums.

The average price for semi-truck brake drums is around $100. You can find some as expensive as $300 and some that are as low as $50.

The labor costs are usually high when it comes to replacing the brake drums. This is because it can be a big job, especially on a semi-truck.

It is also important to keep in mind that brake drums need to be replaced in pairs. This is to keep the wear levels even, similar to how you would with tires and brake discs.

What is the Best Semi Truck Brake Drum?

There are tons of brands to choose from when it comes to brake drums. However, it can be difficult to pinpoint exactly which one is best.

A good best is to go with some of the more reputable manufacturers. These are well known for building the best braking systems on the market.

Here’s our top 5:

  1. Brembo – brake experts who have been in the industry for decades. They do all kinds of brakes, from semi-trucks to racing cars, definitely the go-to trusted brand.
  2. Continental – The German company is well known for its great quality in tires. However, they also build great quality brake drums.
  3. Meritor – With headquarters in Troy, Michigan, Meritor focuses their efforts on building braking systems for all types of commercial vehicles while focusing on reducing maintenance.
  4. WEBB – Webb is a company that specializes in building heavy duty brake drums. These are perfect for semi-trucks.
  5. BWP – This company is one of the most trusted when it comes to brake drums. They have sold over 11 million units worldwide and continue to forge their path as a global leader for commercial braking systems.