2024 Peterbilt 389 Transmission Fluid & Service

Quick Answer

• Transmission Make/Model: Eaton Fuller Advantage Series Automated Manual Transmission (AMT) or Eaton Fuller UltraShift PLUS AMT (depending on configuration)
• OEM Fluid Spec: Eaton PS-386 (or equivalent synthetic 50/75W GL-4 fluid). Always verify with your specific transmission model and owner's manual.
• Drain & Fill Capacity: Varies significantly by transmission model. Typically between 13-17 quarts.
• Full Overhaul Capacity: Varies significantly by transmission model. Typically between 16-22 quarts.
• Filter OEM Part Number: No external filter for Eaton Fuller AMTs. Internal screen/magnet maintenance is typically part of major services, not a routine fluid change.
• Recommended Service Interval:
  • Normal Duty: 400,000 miles or 4 years
  • Severe Duty / Vocational: 250,000 miles or 2 years (e.g., long-haul, heavy-haul, stop-and-go)

Fluid Type Explained

For the 2024 Peterbilt 389, you'll most commonly find an Eaton Fuller Automated Manual Transmission (AMT). These transmissions typically utilize Eaton's proprietary PS-386 fluid specification. This is a high-performance synthetic lubricant designed to provide superior wear protection, thermal stability, and fuel efficiency.

The PS-386 spec is crucial. It ensures the correct viscosity and additive package for the specialized components within these complex automated manual transmissions. Using a fluid that does not meet the PS-386 specification can lead to premature wear, poor shifting performance, increased operating temperatures, and potentially costly transmission damage. While some manufacturers offer equivalent fluids, always ensure they explicitly state compliance with Eaton PS-386. Check your owner's manual or the transmission's data tag for the precise fluid requirement for your specific Eaton Fuller model.

Why Synthetic?

Modern heavy-duty transmissions, especially AMTs, operate under extreme conditions with tight tolerances. Synthetic fluids, like those meeting the PS-386 spec, offer several advantages:

• Extended Drain Intervals: Synthetics maintain their properties longer, allowing for longer service intervals, which translates to reduced downtime and maintenance costs.
• Superior Thermal Stability: They resist breakdown under high temperatures, preventing sludge and varnish formation.
• Improved Cold Weather Performance: Synthetics flow better at low temperatures, ensuring proper lubrication during cold starts.
• Enhanced Wear Protection: They provide a stronger lubricating film, reducing friction and wear on gears, bearings, and synchronizers.

Service Procedure

Servicing an Eaton Fuller AMT involves more than just draining and refilling. While a drain and fill is the most common procedure, it only replaces a portion of the total fluid. For a full fluid exchange, especially during a complete overhaul or significant repair, the entire system would be drained. There is no external filter to replace; instead, some transmissions have an internal magnetic drain plug that should be inspected for metal partículas.

Drain & Fill

This procedure involves draining the fluid from the transmission case and refilling it to the correct level.

1. Preparation: Ensure the truck is on a level surface and the transmission is at operating temperature (for proper drainage). Gather your tools, new fluid, a drain pan, and a torque wrench.
2. Drain: Locate the drain plug on the bottom of the transmission. Place a large drain pan underneath and carefully remove the plug. Allow ample time for the fluid to drain completely. Inspect the drain plug, especially if it