2020 Kenworth T680 Serpentine Belt Routing, Length & Part Numbers

As an ASE-certified master technician, I know firsthand that heavy-duty trucks like the 2020 Kenworth T680 demand rigorous maintenance. A snapped serpentine belt on the highway doesn't just mean a loss of power steering or air conditioning—it means catastrophic overheating, disabled air compressors, and expensive downtime.

Because the 2020 Kenworth T680 is typically equipped with either the Cummins X15 or the Paccar MX-13 engine, accessory layouts can vary. The information below focuses on the highly common Cummins X15 accessory drive belt setup. Always verify against your specific VIN before purchasing parts, as high-output alternators or specific A/C compressors change the required belt length.

Quick answer: Belt Specifications & Part Numbers

• Engine Configuration: Cummins X15 (Accessory Drive)
• Belt Length: 82.0 inches (varies by specific accessory package)
• Rib Count: 8-rib (Heavy-Duty)
• OEM Belt PN: Cummins 3103212 (or Paccar equivalent)
• Aftermarket Cross-References: Gates K080820HD (FleetRunner Micro-V), Dayco 5080820, Continental 4080820
• Auto-Tensioner PN: Cummins 3691280 / Gates 38667
• Idler Pulley PN: Cummins 3691283 / Gates 36000

Belt routing

Pro Tip: Always take a clear photograph of your existing belt routing with your smartphone before you remove the old belt. It is the best reference you can have.

For the Cummins X15 accessory drive setup in the T680, follow this text-based step-by-step routing path. Start at the bottom and work your way up and around:

1. Start by looping the ribbed side of the belt around the bottom of the Crankshaft Pulley.
2. Route the belt straight up to the A/C Compressor.
3. From the A/C compressor, the smooth back of the belt routes over the smooth Idler Pulley.
4. Pull the belt across and wrap the ribbed side around the Alternator Pulley.
5. Route down to the Power Steering Pump (if belt-driven on your specific accessory configuration).
6. Wrap around the Water Pump Pulley.
7. Finally, pull the slack over the smooth roller of the Auto-Tensioner before joining back at the crankshaft.

How to replace the serpentine belt

Replacing the serpentine belt on a Class 8 truck like the T680 requires basic hand tools but a fair bit of leverage due to the heavy-duty tensioner springs.

1. Locate the tensioner: Identify the automatic belt tensioner on the front of the engine block.
2. Release the tension: Insert a 1/2-inch drive breaker bar (or a specialized heavy-duty serpentine belt tool) into the square receptacle on the tensioner arm. Rotate the tensioner arm away from the belt (usually clockwise, but verify based on the tensioner orientation) to relieve tension.
3. Remove the old belt: While holding the tensioner open, slip the belt off the easiest to reach smooth pulley (usually the idler or water pump). Slowly release the tensioner arm back to its resting position.
4. Inspect pulleys: Spin the idler, alternator, A/C, and water pump pulleys by hand. Listen for grinding bearings and feel for excessive play.
5. Install the new belt: Route the new belt following your reference photo or the routing guide above. Leave the tensioner pulley for last.
6. Apply tension: Crank the tensioner open again, slip the belt over the tensioner pulley, and carefully release the breaker bar. Double-check that all ribs are perfectly seated in the grooves of the ribbed pulleys.

Replacement interval

For heavy-duty applications, do not wait for the belt to break. Replace the serpentine belt every 100,000 miles or every 3 to 4 years, whichever comes first. Heavy-duty tensioners undergo millions of cycles; it is highly recommended to replace the automatic tensioner and idler pulleys at the same time as the belt to prevent premature bearing failure.

Signs of a failing belt or tensioner

Keep an eye (and ear) out for these warning signs:

• Squealing or Chirping: Especially upon startup or when the A/C compressor engages. This indicates a stretched belt or a weak tensioner spring.
• Cracking or Missing Chunks: Inspect the ribbed side of the belt. If you see more than 3 cracks per inch, or chunks of rubber missing, replace it immediately.
• Glazing: A shiny, hard surface on the belt means it has been slipping and overheating.
• Tensioner Bounce: With the engine running, observe the tensioner arm. A slight vibration is normal, but excessive bouncing or jumping indicates the internal dampener has failed.
• Uneven Wear: If the edge of the belt is fraying, a pulley is out of alignment or a bearing is collapsing.

If you don't have the tools, the time, or the space to tackle this job on your rig, leave it to the professionals. Find a trusted shop on Repairius.