AMT Clutch Judder When Hot

Clutch replacement is not yet justified. A wear figure of 68% indicates the clutch is part-way through its life, not that it has failed. The key symptom is judder that appears only when hot and under load. That pattern can come from the clutch, but it can also come from engine or gearbox mounts, a contaminated friction surface, a sticking release bearing or actuator, a worn flywheel, a propshaft or driveline fault, or an adaptation/control problem in the AMT system.

The recent actuator calibration is relevant: if the calibration was not completed correctly, or if the actuator air supply or sensor is faulty, the clutch take-up can be uneven. A hot-only judder also suggests a friction or thermal issue, such as oil contamination reaching the clutch when warm, or a flywheel surface problem.

Before authorising a clutch, I would want a road test that reproduces the fault, live clutch and actuator data, a check for oil contamination at the bell housing, mount inspection, and confirmation that the adaptation values are plausible. Replacing the clutch without this could leave the judder unchanged and waste the operator's money.

• Road test: reproduce the judder hot, on a slight incline and loaded if safe. Note whether it occurs in first and reverse, whether it changes with engine speed, and whether it disappears when the clutch is fully engaged.
• Live data: compare clutch position, actuator pressure, engine speed, input shaft speed and torque during take-up. A control fault often shows an inconsistent actuator stroke or a mismatch between requested and actual position.
• Adaptation check: confirm the clutch adaptation values are within the manufacturer's range and that the calibration procedure was completed with the correct air pressure and temperature.
• Air supply: check actuator air pressure, filter condition and leaks. Low or fluctuating pressure can cause uneven engagement.
• Mechanical inspection: check bell-housing area for oil or coolant contamination, inspect engine and gearbox mounts, propshaft joints and centre bearing, and check for excessive flywheel runout or hot spots if the gearbox is removed.
• Cold versus hot comparison: if the judder is absent cold and appears only when hot, friction contamination or thermal distortion is more likely than a simple wear-out.

Only after these checks would I decide whether the fault is in the clutch assembly, the actuation system, the driveline, or the adaptation.

The vehicle should not be presented for test with an unresolved judder that affects pulling away under load. Even if the fault is not a test item in itself, it can affect control, clutch slip, and safe operation, and it may worsen.

I would record the customer complaint, the road-test conditions, the clutch wear value, actuator calibration status, live-data findings, contamination checks, mount and driveline inspection, and the final decision. If the evidence points to contamination or a mechanical clutch fault, I would authorise a clutch inspection and quote for repair with the gearbox removed, but only after confirming the flywheel and actuation system. If the evidence points to adaptation or air supply, I would correct that first and re-test.

If repair cannot be completed before the test, I would advise the operator not to book the test until the vehicle is repaired and road-tested. Releasing it as 'monitor' would not be acceptable for a loaded 18-tonne vehicle with a driver complaint of judder.