Manual transmissions have clutches that transfer energy to selected gear ratios via the driver's shift lever. The energy is transferred through the clutch and pressure plate to the gears. By following the gear patterns, the driver can select any gear for forward momentum or backing up. While an automatic transmission shifts gears by using fluid and pressure, the manual transmission must be shifted by hand. Clutches have their own peculiarities and warning signs when something breaks inside them, gets hung up or slips.
Drive your vehicle on an uphill grade, preferably a slope that has at least a 30-degree incline. Accelerate up the hill as you would normally, starting off in first gear then into second. Keep it in second gear, increasing your speed gradually until you reach just under maximum RPM. Look for any clutch slippage--the engine "revving" higher than normal. This indicates a worn clutch disc.
Drive on the freeway and shift as you normally would from the lowest gear to the highest. Just as you let the clutch out to engage the next gear, check for a slight shimmy or even a heavy shudder when you engage the clutch. A pressure plate with worn springs will not provide solid contact with the clutch disc and cause a noticeable vibration that will travel throughout the vehicle's frame. The vibration may disappear as the vehicle picks up speed in gear. This symptom, known as "clutch chatter," must be remedied by replacing the clutch, pressure plate and throw-out bearing.
Listen for noises coming from the vicinity of the transmission gearbox. The throw-out bearing uses spring force to shove the clutch disc against the pressure plate. The throw-out bearing revolves on bearings; once the bearing dries up and deteriorates, the symptoms can result in a rattling sound in neutral. Most times, the noise goes away while shifting through the gears. A broken throw-out bearing will keep the clutch disc from properly mating with the pressure plate, resulting in no clutch engagement. Sometimes the throw-out bearing will make a rattling sound similar to pebbles in a can.
Place the vehicle on jack stands, either lifting the front two wheels or all four. Look for any gear oil seeping from the clutch housing, located between the block and the gearbox. Any leakage indicates worn seals, and worn seals can allow oil to contaminate the clutch and pressure plate, causing major slippage. A burnt oily odour will accompany this condition.
Sniff the air for the odour of a burnt clutch after a full day of driving. The smell will resemble a hot, stale odour, caused by the burning of asbestos material in the clutch disc. Burnt clutch discs will chatter and slip, sometimes doing both.