2017 Peterbilt 579: Serpentine Belt Routing & Length

Quick Answer

• Belt Length: Varies by engine and accessory configuration. Commonly ~2120mm to ~2475mm.
• Rib Count: 8-rib
• Common Engines: PACCAR MX-13, Cummins ISX15
• OEM Belt PNs: Peterbilt does not publish a single universal PN; PNs are engine- and VIN-specific.
• **Aftermarket Cross-References (examples, verify with your VIN):
  • Gates: K080834 (2120mm), K080975 (2477mm)
  • Dayco: 5080835 (2121mm), 5080975 (2477mm)
  • Continental: 4080834 (2121mm), 4080975 (2477mm)
• **Auto-Tensioner PNs (verify with your VIN):
  • PACCAR MX-13: Gates 38550, Dayco 89255
  • Cummins ISX15: Gates 38587, Dayco 89453
• **Idler Pulley PNs (verify with your VIN):
  • PACCAR MX-13: Gates 36294, Dayco 89018
  • Cummins ISX15: Gates 36009, Dayco 89009

Belt Routing

Before you remove the old serpentine belt, always take a clear photograph of the current belt routing with your phone. This will be your best guide to ensure the new belt is installed correctly. Due to the variations between engine options (PACCAR MX-13 vs. Cummins ISX15) and accessory configurations (with or without factory A/C, different alternator options, etc.), the routing can differ slightly from truck to truck.

However, a common routing path for the primary serpentine belt on a 2017 Peterbilt 579 with the PACCAR MX-13 engine and standard accessories is as follows:

1. Starts at the main crankshaft pulley at the bottom center of the engine.
2. Wraps up and around the A/C compressor pulley.
3. Goes down and around the idler pulley.
4. Travels up to the alternator pulley.
5. Comes across to the power steering pump pulley.
6. Goes down to the water pump pulley.
7. Finally, loops around the automatic tensioner pulley, which provides the installation and removal slack.

Again, your truck's specific routing may vary. Refer to your photograph and the belt routing diagram often found on a decal in the engine bay.

How to Replace the Serpentine Belt

Replacing the serpentine belt on a 579 is a straightforward job for a technician or an experienced operator. The key tool is a long-handled serpentine belt tool or a 1/2-inch drive breaker bar or ratchet, which is used to release the tension on the belt.

1. Safety First: Ensure the engine is off, the parking brake is set, and the truck is on level ground. For added safety, disconnect the batteries.
2. Locate the Tensioner: Find the automatic belt tensioner. It's an spring-loaded arm with a pulley on the end. It will have a square hole (usually 1/2") or a hex feature on it where your tool will engage.
3. Release Tension: Insert your serpentine belt tool or breaker bar into the tensioner arm. Rotate the tensioner to release the spring pressure. This will create slack in the belt.
4. Remove the Old Belt: While holding the tensioner in the released position, carefully slip the old belt off one of the smooth, non-grooved pulleys (like the water pump or idler pulley). Once it's off one pulley, you can gently release the tensioner and remove the belt completely.
5. Inspect Pulleys: With the belt off, now is the perfect time to inspect all the pulleys. Spin each one by hand. They should spin smoothly and quietly. Any roughness, grinding noises, or wobbling indicates a failing pulley bearing that must be replaced.
6. Install the New Belt: Referring to your photograph or the engine diagram, route the new belt around all the pulleys except for one easily accessible smooth pulley (the idler is often a good choice).
7. Apply Tension: Once the belt is correctly routed, use your tool to release the tensioner again. Carefully slide the final loop of the belt over the last pulley. Double-check that the belt's ribs are correctly seated in the grooves of every ribbed pulley.
8. Final Check: Once you are certain the belt is correctly installed, slowly release the tensioner to apply pressure. Give the belt a final visual inspection to ensure it is aligned and not twisted.

Replacement Interval

For a hard-working Class 8 truck like the Peterbilt 579, there is no single, fixed mileage or time interval for serpentine belt replacement. Instead, the belt should be inspected during every routine service (e.g., every oil change or A-service).

As a general guideline, consider replacing the belt proactively every 100,000 to 150,000 miles or every 2-3 years, whichever comes first. The cost of a new belt is minor compared to the cost of a breakdown, downtime, and potential damage to other engine components if the belt fails on the road.

Signs of a Failing Belt or Tensioner

Pay close attention to these warning signs, which indicate your serpentine belt or its tensioner needs immediate attention:

• Squealing or Chirping Noises: A high-pitched squeal on startup or during operation often points to a worn, glazed, or contaminated belt.
• Visible Wear: Inspect the belt for cracks, fraying, missing ribs, or glazing (a shiny, smooth appearance in the grooves).
• Tensioner Pulley Noise: A rumbling, grinding, or rattling sound from the engine bay that changes with RPM can signal a failing bearing in the tensioner or idler pulley.
• Tensioner Arm "Flutter": Observe the tensioner arm with the engine idling. If it is vibrating or bouncing rapidly instead of holding steady, the internal spring mechanism is likely worn out, and the tensioner assembly should be replaced.
• Accessory Malfunctions: Since the serpentine belt drives everything from the alternator to the water pump, a failing belt can cause issues like a "Battery Not Charging" warning or a slowly rising coolant temperature.

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