2019 Peterbilt 579 Serpentine Belt Guide

Quick Answer

• Engine Options: PACCAR MX-13 or Cummins X15
• Belt Length & Rib Count (PACCAR MX-13): ~2475mm (97.4"), 8-rib (Note: Always verify with your VIN as multiple lengths exist)
• OEM Belt Part Number (PACCAR MX-13): Peterbilt 08-08574
• Aftermarket Cross-References (PACCAR MX-13): Gates K080975, Dayco 5080975, Continental 4080975
• Auto-Tensioner Part Number (PACCAR MX-13): Peterbilt 2093593PE
• Idler Pulley Part Number (PACCAR MX-13): Peterbilt 2093594PE
• Belt Length & Rib Count (Cummins X15): ~2195mm (86.4"), 8-rib (Note: Verify with your ESN - Engine Serial Number)
• Aftermarket Cross-References (Cummins X15): Gates K080864, Dayco 5080865
• Auto-Tensioner Part Number (Cummins X15): Cummins 3691282, 5287589
• Idler Pulley Part Number (Cummins X15): Cummins 3691283

Belt Routing

Properly routing the serpentine belt is critical for the function of your engine's accessories. An incorrectly routed belt can cause component damage or slip off the pulleys. Before you remove the old belt, we strongly recommend taking a clear photograph of the existing belt's path for reference.

The typical belt routing for a 2019 Peterbilt 579 with the PACCAR MX-13 engine, without a secondary alternator, is as follows:

1. Starts at the main Crankshaft Pulley (the largest pulley at the bottom).
2. Wraps up and around the Air Conditioning (A/C) Compressor.
3. Goes down and under the smooth Idler Pulley.
4. Travels up to the Alternator.
5. Comes across to the Power Steering Pump.
6. Goes down to the Water Pump.
7. Finally, loops around the Auto-Tensioner arm, which maintains the belt's pressure.

This path ensures each component is driven in the correct direction and with the proper tension.

How to Replace the Serpentine Belt

Replacing the serpentine belt is a manageable task with the right tool. You will need a serpentine belt tool, which is essentially a long, thin breaker bar with various socket and crowfoot attachments. For most tensioners on the Peterbilt 579, a standard 1/2" square drive on a breaker bar is sufficient.

1. Locate the Auto-Tensioner: Find the automatic tensioner pulley, which is mounted on a spring-loaded arm.
2. Release Tension: Fit the 1/2" square drive of your breaker bar or serpentine belt tool into the corresponding square hole on the tensioner arm. Rotate the tensioner arm away from the belt to release the tension. This requires a significant amount of force.
3. Remove Old Belt: While holding the tensioner in the released position, carefully slip the old belt off one of the smooth, non-lipped pulleys, like the idler or water pump pulley.
4. Install New Belt: Following the routing diagram or the photo you took earlier, thread the new belt around the pulleys. Start with the crankshaft pulley and work your way through the path, saving a smooth, easily accessible pulley for last.
5. Finalize Installation: Double-check that the belt is perfectly seated in the ribbed grooves of each grooved pulley. Once confirmed, slowly release the tensioner arm back into position, applying tension to the new belt. The tensioner's indicator mark should fall within the "good" range specified by the manufacturer.

Replacement Interval

For a Class 8 truck like the Peterbilt 579 operating under heavy-duty conditions, a proactive approach to maintenance is key. While there is no universal replacement interval, a general guideline is to inspect the serpentine belt and tensioner at every major service interval (e.g., every 25,000-50,000 miles).

It is recommended to replace the belt every 100,000 to 150,000 miles, or approximately every 2-3 years, regardless of its visual condition, to prevent unexpected failures on the road. It is also best practice to replace the tensioner and idler pulley at the same time as the belt, as their internal bearings wear out over time.

Signs of a Failing Belt or Tensioner

Be alert to the warning signs of a worn-out belt or failing tensioner to avoid a breakdown that could leave you stranded.

• Squealing or Chirping Noises: This is often the first sign, indicating the belt is slipping. The noise may be more prominent during startup, acceleration, or when the A/C is running.
• Visible Wear: Inspect the belt for cracks, fraying, glazing (shiny spots), or missing chunks of the ribs. Any visible damage means the belt needs immediate replacement.
• Tensioner Pulley Misalignment or Wobble: Observe the tensioner and idler pulleys while the engine is running (from a safe distance). If you see any wobble, it indicates a failing bearing.
• Loss of Accessory Function: If your power steering becomes heavy, the battery warning light comes on (alternator not charging), or the engine temperature starts to rise (water pump not circulating coolant), the belt may have failed or is slipping severely.

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