No one knows your vehicle better than you do. If you're wondering if the performance of the vehicle is different to you or you just never noticed it before, chances are it's the vehicle. Knowing when a clutch needs to be replaced is one such diagnosis that can begin by giving off subtle hints and changes in the performance of the vehicle. While there's nothing you can do to prevent or fix it from inevitably going, having it checked soon could likely save other components that could be damaged by ignoring the problem or prolonging the inevitable repair needed.
Look at the tachometer of your vehicle when you're shifting normally. Most standard transmissions have a tachometer gauge on the dashboard to tell the driver when to shift to the next gear. A slipping or worn-out clutch will begin to shift sloppily and you will notice the tachometer indicator moving up and down erratically. This is an excellent visual indication that the clutch needs to be replaced.
Feel the vehicle. Again, no one knows your vehicle better than you. Feeling how the stick shift engages and how the engine reacts to normal shifting is another good test to see how your clutch is performing. If it jerks or jumps abnormally and frequently when upshifting or downshifting, it could also be an indication the clutch is on its way out.
Listen to the engine as you engage the stick shift into gear. This test combines Step 1 and Step 2, but instead of looking at the tachometer or feeling the jerkiness motion of the vehicle, you can listen to how the engine reacts to the normal shifting pattern. If it revs irregularly when the stick shift is engaged in normal shifting, up or down, this would make the tachometer bounce erratically and the vehicle jerk.
Smell the vehicle. When the clutch is going in a vehicle, most often it will omit a pungent burning rubber smell. You may well smell it in the passenger compartment, but you'd also smell it once you parked the vehicle and got out of it. Although the friction material of the clutch is much like the material of a brake shoe, when it is worn and contacts the flywheel improperly, it creates this bad smell that is almost unmistakable and a clear indication the clutch needs to be replaced.
