How to check manual transmission
First, check for oil leaks. There should be no leaks.
Manual transmission test drive:
Now, (with caution – safety first!), shift the transmission lever into neutral. Apply the parking brake. With the engine idling, press the clutch pedal all the way, hold it down, and listen for noises. Then release the pedal and listen for noises again. There should be no loud noises at either positions.
The next step is the test drive.
Try to drive the vehicle at different speeds in all gears, one by one. Every gear should shift smoothly and easily without any noises or jerks. While driving at the second or third gear, try to press down sharply on the accelerator pedal for an instance. The clutch should not slip.
If you feel any slipping (e.g. the engine rpm increases but the speed remains the same), the clutch most likely has to be replaced.
Try to drive with acceleration and deceleration – there should be no grinding, whining or humming noise under any condition. All the gears should shift easily and noiselessly.