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When To Replace Semi Truck Brake Shoes? (For Beginners)

The brakes on any vehicle are an extremely important part. However, they are even more important on semi-trucks because of their weight and the momentum they carry.

Driving with bad brakes can be extremely dangerous, and it’s always important to understand how your brake shoes work and how they wear out.

Read on to find out more about the brake shoes on semi-trucks.

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

The brake shoes on a semi-truck last 100,000 miles on average. This depends on how the semi-truck is driven. If you experience a metallic grinding sound, soft brake pedal, loss of brake pressure, or vibrations through the brake pedal it can be a sign that you need to replace your brake shoes.

How Long do Semi Truck Brake Shoes Last?

There is no set mileage on brake shoes. The truth is that it depends on several different factors. However, brake shoes will last around 100,000 miles on average.

There have been reports of them lasting shorter than that, and drivers claim that their brake shoes have lasted much longer than 100,000 miles.

The main influence on how long a set of brake shoes will last is how the semi-truck is driven. The driving style of the driver is crucial to helping to extend the lifespan of the brakes.

For example, if the driver drives too fast, they will need to brake more often and usually brake sharper, putting more strain on the brakes than there should be.

Another factor that influences the lifespan of the brake shoes is a clean semi-truck. Brake shoes are often damaged by foreign objects in the brake drums, such as rocks or dirt.

Over time the brake shoes on your semi-truck can also begin to fracture and break. This is because of the amount of heat that they need to withstand.

What are The Signs of a Bad Semi Truck Brake Shoe?

It can be difficult to tell what the true condition of your brake shoes is without inspecting them close up.

However, there are some tell-tale signs that you can look out for when the brake shoes begin to wear out.

The first is a metallic scraping or grinding noise while braking. This happens when the friction contact patch wears down, and the sound is caused by metal-to-metal contact.

You may also find that the brake pedal or even the steering wheel will vibrate when you press the brakes. This is down to the brake shoes struggling to grip against the brake drum.

Another sign to look out for is a change in your brake pedal pressure. You might find that the pedal feels softer than it usually does. This is known as brake fade.

While there may be other causes for this, bad brake shoes are one of the causes.

In some cases, you may notice that you need to push the brake pedal down harder to get the brakes to engage to slow you down.

When to Replace Semi Truck Brake Shoes?

It is always best to replace a semi-truck’s brake shoes before they are completely worn out.

It might be tempting to get the most life you can out of a set of brake shoes. However, it’s not always the best thing to do.

When brake shoes wear out, the contact patch between them and the brake drums will be nothing but metal. Metal scraping against metal causes serious damage to the brake drums.

This could result in you having to replace the brake shoes and the brake drums, which will cost you significantly more.

If you leave the replacement of your brake shoes too late, they might wear out at an inconvenient time, such as when you’re on a long trip or a tight schedule.

How to Measure Semi Truck Brake Shoes?

Luckily you can measure your brake shoes to ensure that they still have enough of their friction pad left.

You should do this regularly, especially if you know that they are close to the legally allowed limits for brake shoe wear.

Semi Truck Brake Shoe Wear Indicator

Some brands of brake shoes will have a visual wear indicator. In the majority of cases, this is a painted line on the limit of allowable brake wear.

This makes brake inspections easy as you can check to see how much of the friction pad remains above the wear indicator line.

The minimum allowable brake lining thickness on brake shoes is .25 inches. The indicator line is painted slightly above this limit to give you some leeway.

Other Means to Measure Brake Shoe Wear

You can measure the thickness of your brake shoes by using a tire depth gauge. You simply need to push the depth gauge into the rivets on the brake shoes.

There can be more than eight rivets on a brake shoe. Measure each one to ensure that your brake shoes are wearing evenly all around.

It is important to clean the rivets before using this method, as any dirt or dust caught up inside them can affect your overall measurement.

You can also use a Vernier caliper tool to measure the thickness of your semi-trucks brake shoes. However, you will need to take this measurement from the side of the brake shoes.

Brake Shoe Thickness Chart

Minimum Allowed by DOT (unless wear indicator shows otherwise) ¼ Inch/0.250 inches

Time to Schedule Replacement 0.280 – 0.310 inches

Brand New ½ inch/0.500 inches

Minimum Brake Pad Thickness on a Semi According to DOT

The Department of Transport has some strict regulations, especially when it comes to semi-trucks and their brakes.

“The thickness of the brake lining and pads of non-steering axle brakes on an air-braked commercial motor vehicle shall not be less than 6.4 mm (1/4 inch).

If disc brakes are used, the minimum thickness is 3.2 mm (1/8 inch). If hydraulic or electric brakes are used, the minimum thickness is 1.6 mm (1/16 inch).”

While technically you could still use ¼ inch brake shoes for a couple thousand more miles, DOT sets this as the limit to prevent drivers from leaving worn-out brake shoes on their semi-trucks.

The thickness of your brake shoes can be checked at DOT inspections, and you should always ensure that your brake shoes have a decent amount of life left when you have an inspection coming up.

Can You Drive a Semi With Bad Brake Shoes?

It’s not recommended to drive a semi-truck with bad brake shoes. However, you technically could. If you do drive a semi with bad brake shoes, always drive with extra caution.

Driving with bad brake shoes brings a whole set of risks with it. This could damage not only your semi truck but also endanger your life and the lives of other motorists.

Bad brake shoes can cause extra damage to the brake drums, which means that you will need to replace the shoes and the drums.

This is mainly due to the metal-to-metal friction that happens when brake shoes wear down.

Bad brake shoes will also reduce your semi-truck’s stopping power. This could catch you off guard when you urgently need your brakes.

You might be in a situation where a car cuts in front of you and begins to slow down. However, when you press your brakes, they might not react or be as strong as they used to be.

Do All Semi Truck Brake Shoes have to be Replaced at the Same Time?

Usually, you will replace the brake shoes for two wheels on the same axle at a time. This is to keep track of the wear levels easily.

It also helps to keep the wear levels even on both sides of the semi-truck. This is the same concept as replacing tires.

You will also find that all semi-truck brake shoes are sold in sets for two wheels. This makes it much easier to replace two sets of shoes in one go.

How Often do Semi Truck Brake Shoes Need to be Replaced?

In most cases, a good guideline to replacing the brake shoes in your semi-truck is between 70,000 and 100,000 miles.

It is important to replace them at a convenient time before they reach their allowable wear limit. This will prevent you from being put in a situation where your brakes may suddenly fail.

However, it does depend on how often the semi-truck is driven. If it drives a lot and drives long distances, the brake shoes may wear out quicker.

The driving style of the driver also influences how long the brake shoes will last in your semi-truck. If the driver drives fast and uses the brakes often and brakes sharply, the brake shoes will wear quicker.

Semi Truck Brake Shoe Replacement Cost

The cost of brake shoes varied between different manufacturers depending on their quality and expected lifespan. However, the average cost for one unit is around $50.

Some brake shoes may be cheaper, while others may be much more expensive. Some companies will also sell the brake shoes in sets for two wheels.

The labor costs can be quite high for replacing the brake shoes. On average, it is between $150 and $250 to have them replaced on your semi-truck.

It is highly recommended to use the help of a professional since this is a very important job. Replacing the brake shoes properly is crucial.

If the job is not done correctly, you could risk brake failure or the brakes not working at all.