Frequently Asked Questions About Mack CH/CHN/CHU Truck Drivetrain Parts

What drivetrain components are compatible with my specific Mack CH, CHN, or CHU model year?

Mack CH series trucks (1988-2009) share many drivetrain components, but there are important differences. CH models typically use Eaton Fuller transmissions (13-speed and 18-speed), while CHN and CHU models may have different driveline angles and lengths. Always verify compatibility using your VIN number, especially for driveshafts, U-joints, and carrier bearings. Model years 2000-2009 often require different clutch specifications than earlier models due to engine upgrades.

How difficult is it to replace a clutch assembly on these trucks, and what special tools are needed?

Clutch replacement on CH series trucks requires transmission removal, which typically takes 6-8 hours for experienced mechanics. You'll need a transmission jack rated for at least 350 lbs, clutch alignment tool specific to your flywheel (usually 1.75" or 2"), and torque wrenches capable of 100-150 ft-lbs. The biggest challenge is accessing the top bell housing bolts - many techs recommend removing the shifter tower for better access. Budget for new pilot bearing, throw-out bearing, and input shaft inspection during the job.

What are the signs my driveshaft U-joints or carrier bearing need replacement?

Common symptoms include vibration at specific speeds (usually 45-65 mph for U-joints, 25-35 mph for carrier bearings), clunking during gear changes, or visible rust streaks from the U-joint caps. CH series trucks with tandem axles are particularly hard on rear driveshaft U-joints. Check for play by grabbing the driveshaft and attempting to move it - any movement indicates worn components. Replace U-joints in pairs and always check driveshaft balance after installation.

Which transmission fluid should I use, and how often should I change it?

Most Eaton Fuller transmissions in CH series trucks require SAE 50 weight transmission fluid (not engine oil). Synthetic formulations like Eaton PS-386 provide better shift quality in cold weather. Change intervals depend on application: highway use every 250,000 miles, vocational/heavy hauling every 100,000-150,000 miles. Always check the transmission tag for specific requirements - some Autoshift models require different fluids. Capacity is typically 12-16 quarts depending on auxiliary sections.

What aftermarket drivetrain upgrades provide the best reliability improvements?

The most beneficial upgrades include heavy-duty clutch kits rated 50-100 lb-ft above your engine torque, sealed U-joints (like Spicer Life Series) that extend service intervals to 500,000+ miles, and upgraded carrier bearing assemblies with improved sealing. For trucks with frequent shifting or stop-and-go operation, consider ceramic clutch facings for longer life. Many operators also upgrade to larger diameter driveshafts (5" vs 4.5") when replacing worn components for reduced vibration and increased strength.