Freightliner MT45 Serpentine Belt Replacement Guide (2009-2017)
Keep your MT45 work truck on the road by understanding the signs of a failing serpentine belt and how to choose the right replacement.
- A failing serpentine belt will disable your MT45; symptoms include squealing, visible cracks, and accessory failure.
- For the Cummins 6.7L engine, always replace the belt tensioner and idler pulleys when you replace the belt to prevent repeat failures.
- High-quality aftermarket brands like Gates (especially the FleetRunner heavy-duty line) and Dayco offer OEM-level or better performance for this commercial application.
- If the belt breaks, you cannot drive the truck. The engine will overheat and you will lose power steering and charging capabilities.
Symptoms of a Failing Serpentine Belt
A failing serpentine belt on your MT45 will give you clear warning signs. Ignoring them can leave you stranded. Look and listen for these symptoms:
- Squealing or Chirping Noises: This is the most common sign. You'll hear a high-pitched squeal from the engine bay, especially when you first start the truck or when the engine is under load (like when the A/C kicks on). This noise is caused by the belt slipping on the pulleys.
- Visible Damage: Pop the hood and look at the belt. Signs of trouble include cracks, fraying, missing ribs, or a glazed, shiny appearance on the belt's surface. 🎬 Watch: See these visual signs of a failing belt
- Accessory Malfunctions: Since the belt powers everything, you may notice dimming headlights (failing alternator), a loss of power steering assist (making turning difficult), or an A/C that no longer blows cold.
- Engine Overheating: The serpentine belt drives the water pump. If the belt slips or breaks, the water pump stops circulating coolant, and the engine will quickly overheat. This can cause catastrophic engine damage.
Check the Tensioner and Pulleys
On the Cummins 6.7L engine, the belt tensioner is a very common point of failure. A weak or seized tensioner is often the root cause of belt failure. When you replace the belt, it is critical to also replace the belt tensioner and idler pulleys. Failure to do so often results in the new belt failing prematurely, sometimes within a few thousand miles.
🎬 Watch: Cummins tensioner replacement and things to watch forChoosing the Right Aftermarket Serpentine Belt
For a work vehicle like the MT45, you don't want to compromise on quality. Fortunately, top-tier aftermarket brands offer parts that meet or exceed OEM specifications.
- OEM vs. Aftermarket: The original Freightliner belt provides reliable performance, but high-quality aftermarket options from brands like Gates and Dayco offer the same or better quality, often at a lower price. In fact, Dayco is believed to be the manufacturer for the original Cummins tensioner.
- Brand Tiers (Good, Better, Best):
- Good: A standard replacement belt from a known brand like Dayco or Gates will serve you well. These are made from durable EPDM rubber and meet OEM standards.
- Better/Best: For a commercial vehicle that sees heavy use, long idle times, and high mileage, upgrading to a heavy-duty belt is highly recommended. Look for products like the Gates FleetRunner line. These belts are built with superior materials like aramid reinforcement to better resist heat and stretching, providing a longer service life in demanding applications.
Typical Replacement Costs
Costs can vary by region and shop, but here are some estimates for replacing the serpentine belt on a 2009-2017 Freightliner MT45.
| Part/Service | Estimated Cost |
|---|---|
| New Aftermarket Serpentine Belt | $21 - $95 |
| New Aftermarket Tensioner & Idler Pulley Kit | $60 - $150 |
| Shop Labor | $100 - $200 |
| Total (DIY) | $81 - $245 |
| Total (Installed at Shop) | $181 - $445 |
Frequently Asked Questions
How often should I replace the serpentine belt on my MT45?
A good rule of thumb is to inspect the belt at every oil change and plan for replacement between 60,000 and 100,000 miles. However, for a commercial vehicle, replacing it proactively around the 60,000-mile mark, along with the tensioner, is cheap insurance against a breakdown.
Do I really need to replace the tensioner with the belt?
Yes. On the Cummins 6.7L engine, the tensioner is a known weak point. A failing tensioner pulley or a weak spring will destroy a new belt quickly. Replacing the belt, tensioner, and idler pulleys as a set is the correct way to do the job and ensure long-term reliability.
What is the difference between a standard and a heavy-duty belt?
Heavy-duty belts, like the Gates FleetRunner series, use stronger internal cords (often aramid) and more robust rubber compounds. This makes them more resistant to stretching, heat, and contamination from oil or coolant, which is ideal for the high-heat, high-mileage life of a commercial truck engine.
What tools do I need to change the serpentine belt?
The primary tool needed is a long-handled 1/2-inch drive ratchet or breaker bar to release the spring pressure on the belt tensioner. You will also need a socket (typically 13mm) to unbolt the tensioner itself for replacement. Always make sure to draw a diagram or take a picture of the belt routing before you remove the old one.
🎬 See this walkthrough for replacing the belt without removing the fanHelpful Videos
Technical Specifications
OEM Part Numbers: 5264021
Belt material is typically EPDM (Ethylene Propylene Diene Monomer) rubber. Reinforcement cord material is polyester or aramid for heavy-duty versions. The belt for the main drive on the 6.7L engine is an 8-rib K-section belt.
We Have This Part in Stock
The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- Freightliner MT45: