Why does the car not move when in gear?
2 Answers
When a car is in gear but does not move, it is a functional comprehensive fault involving the clutch, transmission, and drive axle. Diagnosis should first determine the fault location, starting with checking the condition of both wheels. The diagnostic sequence generally proceeds from the drive wheels forward through the rear axle to the driveshaft, then to the transmission, and finally to the clutch. Below are the relevant details: Inspect the half-shaft: If the driveshaft rotates but the car does not move forward, the fault lies in the rear axle. Lift the rear axle and rotate one rear wheel. If the other rear wheel rotates in the opposite direction but the driveshaft does not follow, it indicates that all the rivets of the differential bevel gear are sheared. If the other rear wheel does not rotate, inspect the half-shaft for breakage. Check the transmission: If the car is started in a certain gear and the driveshaft does not rotate, the fault is in the transmission. Remove the transmission cover and inspect whether the transmission shift fork is broken or if the guide block fixing screws are loose. If the above checks are normal, conduct a gear engagement test. If the second shaft does not rotate in a certain gear, it indicates that the half-moon key of that gear is sheared. If the second shaft rotates in direct drive but does not rotate in other gears, it means the intermediate shaft support bearings at both ends are disassembled, causing the intermediate shaft to drop. If the driveshaft does not rotate in any gear, the fault lies in the clutch. Check whether the clutch is severely slipping, whether all the spline teeth of the driven plate hub and steel plate rivets are sheared, or whether the steel plate is fractured.
Yesterday my car did the same thing - stepped on the gas in D gear but it wouldn't move! The most common cause is burnt clutch plates, especially in older cars. Last time I towed it to the repair shop, the mechanic said the pressure plate springs had weakened causing slippage, and the whole set needed replacement. If the driveshaft snaps with a crack sound, the wheels won't turn at all. For automatic transmissions, check if the transmission fluid has turned black and smelly, or if the valve body is stuck causing low oil pressure. Oh, and for cars with electronic shifters, remember to check if the gear position sensor got waterlogged - my neighbor's flood-damaged car had exactly this issue. If the engine revs loudly when shifting but the car doesn't move, nine times out of ten there's a drivetrain problem.
