2017 Kenworth T680 Transmission Fluid Capacity, Type & Service Info

The 2017 Kenworth T680 is a flagship Class 8 truck renowned for its aerodynamics and driver comfort. Whether you are running linehaul across the country or managing regional distribution, the transmission in your T680 is the beating heart of your driveline. Because these trucks are highly customizable, they can be spec’d with a variety of transmissions, including Eaton Fuller manuals, Eaton UltraShift Plus automated manual transmissions (AMTs), and Allison heavy-duty automatics. Maintaining these gearboxes with the correct fluid and service intervals is critical to maximizing uptime and protecting your investment.

As an ASE-certified master technician, I have compiled this comprehensive guide to help you service the transmission in your 2017 Kenworth T680.

Quick answer: 2017 Kenworth T680 Transmission Specifications

• Transmission Make/Model: Eaton Fuller Manual (e.g., 10-speed, 13-speed, 18-speed RTLO series), Eaton UltraShift Plus (AMT), or Allison 3000/4000 Series Automatic.
• OEM Fluid Spec:
  • Eaton Transmissions: Eaton PS-386 Synthetic Transmission Fluid.
  • Allison Transmissions: Castrol TranSynd or any TES 295 / TES 668 approved synthetic ATF.
• Drain & Fill Capacity:
  • Eaton Manual/AMT: 22 to 28 pints (11 to 14 quarts), depending on the exact model (e.g., RTLO-18918B takes approx. 28 pints).
  • Allison 4000 Series: Approximately 39 to 43 quarts (verify pan depth).
• Full Overhaul Capacity: Typically 1 to 2 quarts more than the standard drain and fill capacity (dry fill).
• Filter OEM Part Number:
  • Eaton: No internal fluid filter for standard manual/AMT gearboxes.
  • Allison: Allison high-capacity spin-on filter kit (OEM Part # 29558118 for 4000 Series). Always verify with your dealer or service manual based on your exact VIN.
• Recommended Service Interval:
  • Eaton PS-386 (Linehaul): 500,000 miles.
  • Severe Duty/Vocational: 180,000 miles or 3 years.

Fluid type explained

For the 2017 Kenworth T680 equipped with an Eaton Fuller transmission (both manual and the UltraShift Plus AMT), the absolute gold standard is Eaton PS-386 synthetic transmission fluid. This fluid replaced the older PS-164 rev 7 specification. PS-386 is specifically engineered to improve fuel economy, reduce operating temperatures, and provide superior gear wear protection under immense torque loads. Do not use standard gear oil or API GL-5 in these transmissions, as the sulfur-phosphorus additives can destroy the synchronizers and internal components.

If your T680 is equipped with an Allison automatic (often spec'd for vocational or specific regional haul applications), you must use a fluid that meets the TES 295 or the newer TES 668 specification. These synthetic fluids offer exceptional thermal stability, preventing varnish and sludge buildup during heavy towing and constant stop-and-go operation.

Service procedure

Servicing an Eaton transmission is relatively straightforward but requires attention to detail. Because these gearboxes do not have torque converters, the drain and fill capacity is virtually identical to the overhaul capacity.

1. Preparation: Drive the truck to bring the transmission fluid up to normal operating temperature. This helps suspend any contaminants and allows the thick synthetic fluid to drain quickly.
2. Draining: Locate the drain plug at the lowest point of the transmission case. Remove the fill plug on the side first (to prevent a vacuum lock and ensure you can refill it), then remove the drain plug. Inspect the magnetic drain plug for large metal shavings—a small amount of fine "fuzz" is normal, but chunks indicate internal bearing or gear failure.
3. Refilling: Clean and reinstall the drain plug. Fill the transmission through the side fill hole using a fluid pump until the fluid is level with the bottom of the fill hole.
4. Allison procedures: If servicing an Allison automatic, the procedure involves draining the pan, replacing the external spin-on filters (or internal cartridge filters depending on the exact configuration), and carefully measuring the fluid level using the push-button shift selector's oil life monitor or a physical dipstick once the fluid reaches operating temperature.

Service interval

Heavy-duty commercial vehicles operate under vastly different conditions, which dictates the maintenance schedule:

• Normal / Linehaul Duty: For a Kenworth T680 pulling legal weight (80,000 lbs gross) on highway routes, Eaton recommends a fluid change every 500,000 miles when using PS-386 fluid. Allison TES 295 intervals typically stretch to 300,000 miles for linehaul operations.
• Severe Duty / Vocational / Heavy Haul: If your T680 is running overweight permits, frequent mountain grades, or primarily stop-and-go regional routes, the interval drops drastically. Eaton recommends fluid changes every 180,000 miles or 3 years (whichever comes first).

Common transmission problems

The 2017 Kenworth T680 is a highly reliable machine, but its transmissions are not immune to wear and tear.

For the Eaton UltraShift Plus AMT, the most common issues are related to the electronic and pneumatic controls rather than the mechanical gears. The XY Shifter (the mechanism that physically moves the shift rails) is a known weak point and can fail, leaving the truck stuck in gear or unable to select a gear. Similarly, the electric clutch actuator (ECA) can bind or fail, causing harsh engagements or "clutch fault" codes on the dash. Wiring harness chafing along the transmission housing is another common electrical gremlin that can cause intermittent shifting issues.

For standard Eaton Manuals, the most frequent problems stem from driver abuse or poor air supply. A leaking range valve or splitter valve (due to contaminated air from a failing air dryer) can cause slow or grinding range shifts.

If you are experiencing hard shifting, grinding, or flashing dash codes, don't wait for a total breakdown on the side of the highway.

Find a trusted shop on Repairius.