Automatic transmissions are more common these days, but for people who still enjoy the hands-on approach, a manual, or standard, transmission can present a few problems. Your car's engine transfers power to the transmission via a clutch. Sector forks in the transmission select which gear will be put into use. Although there are components to prevent gears from grinding or sticking, sometimes gears do fail to engage. If this happens, there are a number of things to look for before talking to a mechanic.
Check your transmission fluid. Transmission fluid lubricates the moving parts of your transmission. You should check your fluid every 30,000 to 60,000 miles in a manual transmission car. Failure to do so can cause your transmission fluid to become contaminated with bits of metal from the bearings, synchronisers and gears. This can make shifting difficult or impossible. Because transmissions give few signals when their fluid is low, it's important to be consistent about checking it. You may also need to upgrade to a different type of fluid if you find that your transmission problems are happening during cold weather, or if you are using a fluid not originally recommended for your vehicle.
Listen for gear clashing and grinding. Grinding gears will result in a grating sound as you shift between gears. If this is the case, the trouble may be in your synchronisers. Sychronizers are positioned between the two main drive gears and are responsible for locking the gears into the correct speed with the engine. Synchro rings that match the width and depth of the gears on the main shaft can also become worn or bent. Once this happens, your car may fail to shift.
If your transmission cannot be put into gear when the car is running but you can change gears with the engine off, the problem could be with your pressure plate or clutch disk. Your clutch disk should be checked every 15,000 miles (or less if you engage in stop and go, city driving). There is no way to determine if your pressure plate or clutch disk are bad without dismantling the bell housing of the transmission. If you suspect either are worn, it's probably best to replace them.
If your clutch engages close to the floor, or if it moves easily but does not allow you to shift, the clutch linkage may have become disconnected or the clutch cable may have snapped. Worn clutch pedal bushings will cause the same problems. Check with your mechanic to determine if you need to replace the entire clutch assembly or individual components of the clutch.