Manual transmissions are still common in heavy trucks and in plenty of older diesel pickups, and automated manuals use a clutch too. A clutch that slips, chatters or will not release cleanly wears fast and takes the flywheel and transmission with it if ignored. RDI Power repairs clutches in Brooksville on diesel pickups, medium-duty trucks and Class 8 tractors.
Signs of clutch trouble
- Slipping: rpm climbs but road speed does not, especially loaded or uphill.
- Chatter or shudder: a shake on takeoff as the clutch engages.
- Hard shifting or grinding: the clutch is not fully releasing.
- Engagement point changed: the pedal grabs very high or very low.
- Noise with the pedal down: a release bearing on its way out.
- Burning smell after a hard pull.
Heavy truck clutches
Most manual tractors run Eaton Fuller transmissions with a pull-type clutch. Manual-adjust clutches need their free travel set as the linings wear; self-adjusting designs handle it on their own but still need inspection. The clutch brake, engaged when the pedal goes to the floor, stops the countershaft so the driver can shift into first or reverse at a stop. A worn clutch brake is behind many complaints of grinding at a stop. Pedal free play, release bearing clearance and clutch brake squeeze all get measured during service.
Diesel pickup clutches
Diesel pickups with manuals deliver a lot of torque through a relatively small clutch:
- Ram: NV4500 and NV5600 manuals on older trucks, then the G56 6-speed.
- Ford: the ZF 6-speed behind 7.3 and 6.0 Power Stroke engines.
- GM: a ZF 6-speed was offered behind early Duramax engines.
Ram’s G56 and Ford’s ZF6 trucks used dual-mass flywheels, which absorb vibration but wear out and can rattle or fail. When replacing a clutch on those trucks, the flywheel needs inspection, and sometimes replacement. Hydraulic clutch systems, the master and slave cylinders and their lines, cause release problems of their own. More platform detail is on our Ram and Dodge page.
Automated manual clutches
Detroit DT12, Volvo I-Shift and Mack mDRIVE transmissions use a dry clutch worked by an actuator. Clutch wear shows up as slow or harsh engagement, fault codes or a truck that struggles to launch. After a clutch replacement, these transmissions need a calibration with diagnostic software. Air supply problems can mimic clutch faults on air-actuated units, so we check that too.
Clutch diagnosis
We road test to confirm slipping, chatter or release problems, then measure pedal height, free play and engagement. Hydraulic systems get checked for leaks and air. On heavy trucks, we inspect clutch brake operation and adjustment. When the transmission comes out, we look for oil on the clutch from a leaking rear main seal or transmission input seal, check flywheel condition and inspect the pilot bearing. If a clutch failed early, we want to know why.
Clutch repair work
- Clutch adjustment on manual-adjust heavy-duty clutches
- Clutch brake replacement
- Clutch kit replacement: disc, pressure plate, release bearing and pilot bearing
- Flywheel resurfacing or replacement, including dual-mass flywheels
- Hydraulic master and slave cylinder repair
- Rear main or input seal repair if oil caused the failure
- Calibration on automated manuals
Added power and clutches
A clutch is sized for the engine’s factory torque. A truck that has been tuned for more power, or that tows near its limit every day, may need a heavier-duty clutch to hold. See our notes on engine tuning before adding power to a manual truck. Transmission work beyond the clutch is on our transmission repair and rebuild page.
If your clutch is slipping, grabbing or making shifts harder, bring the truck in before it damages the flywheel.