If a manual car will not go into gear while the engine is running but shifts fine with the engine off, the clutch is not fully disengaging. The usual causes are low or leaking clutch hydraulic fluid, air in the hydraulic system, a failing master or slave cylinder, a stretched clutch cable, or a warped or sticking clutch disc. Worn synchros and shift linkage problems cause grinding or difficulty in specific gears. On automatics, a car that will not go into gear points to the shifter, the interlock or the transmission itself.
Manual: diagnose by symptom
| Symptom | Likely cause |
|---|---|
| Won’t go into any gear while running, fine with engine off | Clutch not releasing: hydraulics, cable or disc |
| Clutch pedal goes to the floor or feels soft | Low fluid, a leak, air, or a failing master or slave cylinder |
| Grinds going into one gear | Worn synchro for that gear |
| Shifter feels loose or vague | Worn shift linkage bushings or cables |
| Hard to shift when cold only | Gear oil too thick, or the wrong type |
Check the clutch hydraulics
Most modern manuals use a hydraulic clutch. Check the clutch fluid reservoir, which often shares fluid with the brakes, and look for leaks at the slave cylinder and inside the cabin under the pedal. Bleeding the system removes air; a cylinder that leaks needs replacing.
Won’t go into gear after replacing the clutch
After a clutch job, the common causes are air in the hydraulics, a slave cylinder not seated correctly, the wrong disc orientation, a pilot bearing that binds, or a disc that does not slide freely on the input shaft splines. Re-bleed first, then check the installation.
Automatic won’t go into gear
On an automatic, a shifter that will not leave park is usually the brake-shift interlock; see shifter stuck in park. If the shifter moves but the car will not drive, see car won’t move in drive.
Intermittent problems
A clutch that sometimes releases and sometimes does not suggests a slowly failing master cylinder that loses pressure, or air that moves around in the system. A shift problem that comes and goes with temperature often points to fluid or gear oil.
Clutch wear
A worn clutch usually slips rather than refusing to release, but a damaged disc can do both; see signs of a bad clutch, clutch slipping and clutch chatter. If the gearbox itself is worn, compare a rebuild with our transmissions.
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