2024 Kenworth T680 — Serpentine Belt Routing & Length

Quick answer

• Belt length: Engine- and accessory-dependent on the 2024 T680. Do not order by model/year alone. Confirm by VIN/ESN and accessory drive layout.
• Rib count: Typically 8‑rib Micro‑V on PACCAR MX‑11/MX‑13 and Cummins X15 packages; verify on your truck.
• OEM belt PN: Varies by engine (PACCAR/Kenworth for MX‑series; Cummins for X15). Use your VIN or engine serial number to pull the exact OE number.
• Aftermarket cross‑refs: Match to OE PN and belt size. Common heavy‑duty series include Gates FleetRunner Micro‑V (K08xxxx), Dayco Gold Label Poly‑V (508xxxx), and Continental/ContiTech HD (408xxxx).
• Automatic tensioner PN: Varies by engine bracket and accessory option (common suppliers: Litens, Gates DriveAlign, Dayco). Cross‑reference by OE PN or bracket casting.
• Idler pulley PN: Varies by diameter/offset; match by OE PN and physical dimensions.

Note: The T680 can be built with PACCAR MX‑11, PACCAR MX‑13, or Cummins X15. Each uses different belts/tensioners based on alternator output, A/C compressor style, and whether the A/C runs on the main belt or a separate stretch belt. Always decode by VIN/ESN before purchasing.

Belt routing

We can’t show a diagram here, so take a clear photo of your existing belt from multiple angles before removal. On most 2024 T680 configurations with a single main serpentine belt, the routing is as follows (grooved side on grooved pulleys; smooth/backside on smooth pulleys):

1. Crankshaft pulley (harmonic balancer) — starting point at the bottom.
2. Up and to the A/C compressor — belt wraps the A/C pulley with the grooved side.
3. Across a smooth idler — backside of the belt rides over the idler to change direction.
4. Over the alternator — grooved side engages alternator pulley at the top/front.
5. Down to the power steering pump — grooved side on the pump pulley.
6. Up/backside over the water pump — many HD water pumps have a smooth pulley driven on the belt’s backside for reverse rotation.
7. Around the automatic tensioner — typically a smooth pulley; route the backside and allow the tensioner to take up slack.
8. Return to the crankshaft pulley — confirm all ribs are fully seated in every grooved pulley.

Some variants place the idler and tensioner in the opposite order, or run the A/C on a separate stretch belt. If your truck has two belts, this description applies to the main accessory drive; service the A/C stretch belt separately per engine procedure.

How to replace the serpentine belt

• Tools: serpentine belt tool or a long 1/2" breaker bar for the tensioner square drive; flashlight; mirror; paint pen or phone camera.
• Preparation: Park safely, set brakes, chock wheels, and key off. If equipped, use battery disconnect. Allow engine to cool.

Steps:

1. Photograph the existing routing and sketch a quick map. Note pulley types (smooth vs grooved) and wrap directions.
2. Inspect the tensioner: identify the square drive or hex boss. Rotate the tensioner (usually clockwise on MX‑series and X15, but verify) to relieve belt tension.
3. Slip the belt off the easiest upper pulley (often the alternator) while holding the tensioner released, then ease the tensioner back to rest.
4. Remove the belt fully. Spin idlers and the tensioner pulley by hand; replace any rough/noisy units. Check alignment and clean any oil/coolant contamination.
5. Route the new belt according to your photo/map, leaving one easy‑access pulley for last. Ensure every groove is engaged and the backside rides only on smooth pulleys.
6. Rotate the tensioner again and slip the belt onto the last pulley. Release the tensioner slowly.
7. Double‑check seating on all pulleys. Bump the starter or bar the engine over one full revolution, then recheck tracking.
8. Start the engine, observe tracking for 30–60 seconds, and listen for chirps/squeal. Reinstall any shrouds/guards.

Tip: If your A/C uses a separate stretch belt, replace it now. Use the correct stretch‑belt tool; do not pry with screwdrivers.

Replacement interval

• Inspection: At every PM service (roughly 15,000–25,000 miles or monthly for severe duty). Use a rib‑wear gauge if available.
• Replacement: Common fleet practice is 100,000–150,000 miles or 2–3 years, sooner if cracks, chunking, or glazing are found. Replace the automatic tensioner and idlers with every second belt, or immediately if any bearing play, noise, or arm flutter is observed.

Environmental factors (heat, dust, oil/coolant leaks) can shorten life dramatically; address leaks before installing a new belt.

Signs of a failing belt or tensioner

• Belt: chirping at idle or on wet start, high‑pitched squeal under load, frayed edges, rib cracking or chunking, glazing/shiny ribs, black belt dust, or contamination from oil/coolant.
• Tensioner/idlers: visible arm flutter, misalignment, pulley wobble, seized or gritty bearings, belt tracking off‑center, or repeated belt noise shortly after replacement.
• Vehicle symptoms: battery/charging warnings (alternator slip), elevated coolant temps (water pump slip), heavy steering (PS pump slip), weak A/C at idle (compressor slip).

Engine‑option variation and part‑number guidance

• PACCAR MX‑11/MX‑13: Typically 8‑rib single serpentine; some builds use a separate A/C stretch belt. Order by VIN through Kenworth/PACCAR or cross‑reference with Gates/Dayco/Continental using the OE PN.
• Cummins X15: Also commonly 8‑rib; accessory placement can differ. Order by ESN through Cummins QuickServe or a dealer and then cross‑reference.

Because 2024 model‑year accessory drives vary (alternator amperage, A/C compressor type, belt count), do not rely on generic lengths. Use your VIN or ESN to retrieve the exact OE belt, tensioner, and idler part numbers, then match to aftermarket as needed (e.g., Gates FleetRunner K08 series, Dayco 508 series, Continental 408 series).

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