2015 Peterbilt 579 Serpentine Belt Guide

Quick Answer

• Belt Length: 2415mm (95.1 inches)
• Rib Count: 8
• OEM Belt Part Number: Peterbilt 07-08085
• Aftermarket Cross-References:
  • Gates K080951
  • Dayco 5080950
  • Continental 4080951
• Auto-Tensioner Part Number: Peterbilt 07-08082 (cross-refs to Gates 38584, Dayco 89470)
• Idler Pulley Part Number: Peterbilt 07-08081 (cross-refs to Gates 36298, Dayco 89138)

Belt Routing

Before you remove the old belt, always take a clear photograph of the routing path with your phone. This can be a lifesaver if you get interrupted or second-guess the routing. On a 2015 Peterbilt 579 with the PACCAR MX-13 engine, the serpentine belt follows this path:

1. Starts at the main crankshaft pulley at the bottom.
2. Wraps up and around the A/C compressor pulley.
3. Goes down and under the smooth 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, wraps around the auto-tensioner pulley, which applies pressure to the system.

How to Replace the Serpentine Belt

Replacing the serpentine belt is a common maintenance item. You'll need a serpentine belt tool or a long-handled 3/8" or 1/2" breaker bar.

1. Safety First: Make sure the engine is off and cool. Disconnect the batteries to prevent accidental starting.
2. Locate the Tensioner: The auto-tensioner is typically located near the water pump. It has a square hole (usually 3/8" or 1/2") or a hex-shaped lug cast into its body.
3. Release Tension: Insert your breaker bar or serpentine belt tool into the designated spot on the tensioner arm. Rotate the tensioner arm to release the tension on the belt. This can require a good amount of force.
4. Remove Old Belt: While holding the tensioner, slip the old belt off one of the smooth, non-lipped pulleys like the idler or water pump.
5. Inspect Pulleys: With the belt off, spin each pulley by hand (except the crank, of course). They should spin smoothly and quietly. If you feel any roughness, grinding, or wobble, the pulley bearing is failing and it should be replaced. Check the tensioner for smooth movement and adequate resistance.
6. Install New Belt: Following the routing path you photographed earlier, carefully thread the new belt around all the pulleys, saving a smooth, easily accessible pulley for last.
7. Apply Tension: Release the tensioner arm again and slip the belt over the final pulley. Double-check that the belt is centered in the grooves of every ribbed pulley. An incorrectly seated belt will shred itself almost immediately upon engine start.
8. Final Check: Once you're certain the belt is correctly routed and seated, reconnect the batteries, start the engine, and let it run for a minute to ensure everything is operating smoothly.

Replacement Interval

For a heavy-duty application like the Peterbilt 579, a comprehensive belt and tensioner inspection is recommended every 100,000 miles or annually. While modern EPDM belts are durable, they often fail without the visible cracking of older neoprene belts. A general rule of thumb is to replace the serpentine belt, tensioner, and idler(s) proactively every 250,000 to 300,000 miles to prevent a breakdown on the road.

Signs of a Failing Belt or Tensioner

• Squealing Noise: A high-pitched squeal, especially on startup or when the engine is under load (like when the A/C kicks on), is a classic sign of a slipping belt.
• Visible Wear: Look for fraying, glazing (a shiny, smooth appearance on the belt's underside), or missing ribs.
• Tensioner Noise: A rattling or grinding sound from the engine bay at idle can point to a failing bearing inside the tensioner or idler pulley.
• "Belt Flutter": Watch the long spans of the belt with the engine running. Excessive vibration or flutter indicates the tensioner is weak and no longer able to properly dampen belt vibrations.
• Accessory Malfunctions: If your power steering feels heavy or the battery light flickers, it could mean the belt is slipping and not properly driving the accessories.

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