Drive Train Systems
Power flow and driveline geometry
Follow power from the flywheel to the road: clutch or torque converter, transmission, driveshaft, differential, axles. Clutch questions turn on release-bearing contact, free play, and the difference between a clutch that slips under load (worn disc or weak pressure plate) and one that drags (does not release fully, causing hard shifting and gear clash). Automatic and automated manual transmissions add converter stall, clutch and valve-body adaptation, and relearn procedures after repair.
Driveshafts test your understanding of phasing and angles. Universal joint yokes must be in phase - the joints at each end aligned - or vibration results. Working angles at each joint should be equal and opposite within a small tolerance; too much angle causes vibration and shortened joint life. Check runout with a dial indicator and look for missing balance weights. Slip yokes and splines need the specified lubricant, and carrier bearings must be preloaded correctly.
Differentials: ring-and-pinion backlash measured with a dial indicator, pinion preload with an inch-pound torque wrench, correct hypoid lubricant, and the correct axle ratio, which sets cruise rpm and speedometer accuracy. Tandem axles use an interaxle differential or power divider; locking differentials must never be engaged on dry pavement.
Worked example - ratio by revolution count. Raise one wheel, rotate the tire exactly 20 turns and count driveshaft turns. With one wheel held, ratio ≈ 2 × driveshaft turns ÷ tire turns. So 41 driveshaft turns for 20 tire turns gives 2 × 41 ÷ 20 ≈ 4.10:1.