Is it normal to rev in neutral but not in gear?
4 Answers
Revving in neutral is normal while revving in gear is not, here are the specific details: 1. Reason: When revving in neutral, the vehicle load is very small, whereas revving in gear puts a large load on the vehicle, causing severe exhaust pipe resonance. 2. Revving in neutral: Although the gear is in neutral, the engine's power keeps the transmission input shaft rotating through the clutch. When you rev in this state, except for the output shaft and the synchronizers of each gear not rotating, components like the input shaft, countershaft (also known as primary and secondary shafts, though transmission structures may vary), and the constant-mesh gears on the shafts will change speed according to the engine RPM. Revving in neutral or coasting in neutral over long distances can damage the transmission, potentially leading to wear, burning, or noise in the input shaft bearings, synchronizer gears, and synchronizers.
When the engine revs high in neutral but the car won't move when in gear, it's most likely a slipping clutch. I had the same issue with my old manual Passat—it would just roar without moving when I shifted and accelerated. Later, upon inspection, the clutch disc was worn down to the rivets. This usually happens with older cars or vehicles frequently driven with partial clutch engagement. Besides clutch issues, it could also be worn synchronizers in the transmission preventing gear engagement, or excessive engine carbon buildup causing insufficient torque after shifting. If you notice intermittent power loss along with a burning smell, stop immediately and call a tow truck. Forcing it to drive could damage the flywheel.
Lack of power when shifting gears is quite common, and I've encountered several cases while repairing cars myself. The main reasons lie in the power transmission system: either the clutch plate is severely worn and slipping, causing the engine RPM to rise but the wheels not to move; or the torque converter or valve body in an automatic transmission model is malfunctioning. It could also be due to insufficient fuel supply from the fuel pump, which is adequate at idle but can't keep up when shifting gears. If there's a metallic grinding noise when shifting, there might be an issue with the transmission gears. A simple test is to find a slope, shift into first gear, release the clutch without pressing the accelerator—if the car doesn't stall, it indicates the clutch is indeed slipping. In such cases, repair it as soon as possible; driving like this is too dangerous.
Neutral gear works fine but shifting is abnormal, which is basically a clutch issue. For manual transmission cars, this happens when the clutch disc wears thin - you step on the gas and the engine roars but the speed doesn't increase. For automatic transmissions, it could be a failed torque converter lock-up clutch or insufficient transmission fluid pressure. I remember once helping a neighbor check his 120,000 km Corolla - it revved smoothly to 4000 RPM in neutral, but felt like being dragged when in D gear. Changing the transmission fluid immediately solved the problem. Remember not to ride the clutch for long periods, avoid coasting in neutral with automatics, and change transmission fluid regularly.
