Frequently Asked Questions About Kenworth T680 Drivetrain Parts
Will these drivetrain parts fit my specific year model T680, and are there differences between the standard and high-torque versions?
Most drivetrain components for the T680 are compatible across model years 2013-present, but there are important distinctions. Standard T680 models typically use the DT12 automated transmission, while high-torque and heavy-haul configurations may have the Fuller 13 or 18-speed manual transmissions. Always verify your specific transmission model (found on the transmission tag) before ordering clutch kits, yokes, or driveshaft components. Pre-2017 models may require different U-joint sizes, particularly for the rear driveshaft assembly.
What are the most common signs that my T680 driveshaft or U-joints need replacement?
Watch for vibration that increases with speed, clunking sounds during gear changes, or visible rust streaks from the U-joint caps indicating seal failure. For T680s with over 300,000 miles, inspect the carrier bearing for play and check driveshaft balance weights haven't shifted. Many drivers report that aftermarket heavy-duty U-joints last 50-75% longer than OEM parts in severe service applications. Replace U-joints in pairs on the same driveshaft to maintain balance.
Can I upgrade my T680 differential to a different gear ratio, and what ratios work best for my application?
Yes, the T680 rear differentials can be regeared, but it requires matching the ratio to your transmission and intended use. Highway trucks typically run 2.64-2.79 ratios for fuel economy, while vocational applications benefit from 3.55-4.11 ratios. Remember that changing ratios affects your speedometer calibration and may require ECM programming. Most T680s use the Meritor RT-40-145 or RT-46-160 rear differentials, which accept standard Meritor gear sets.
What's involved in replacing clutch components on my T680, and can I do it without dropping the transmission?
Manual transmission T680s require transmission removal for clutch replacement, which typically takes 6-8 hours in a properly equipped shop. You'll need a transmission jack, clutch alignment tool, and proper torque specifications. Common mistakes include not checking the flywheel for heat cracks or failing to replace the pilot bearing. For DT12 automated transmissions, clutch actuator issues are more common than actual clutch wear and can often be diagnosed with diagnostic software before committing to a full clutch replacement.
Which aftermarket drivetrain parts offer the best value without sacrificing reliability?
For U-joints and driveshaft components, Spicer Life Series (SPL) parts consistently outlast standard replacements by 2-3 times in long-haul applications. Eaton Advantage clutches provide excellent heat dissipation for heavy-haul T680s and typically last 400,000-500,000 miles with proper adjustment. For differential rebuilds, Timken bearing sets and Meritor genuine gear sets offer the best balance of longevity and cost. Avoid economy U-joints under 1810 series size for any T680 application, as they fail prematurely under the truck's torque output.
