When attempting to move off, you keep stalling your car due to one, or a combination of the following reasons:
- You bring the clutch pedal up too quickly
- You’re not pressing the accelerator pedal enough
To better understand why you keep stalling your car, it helps if you know a little bit about the car’s clutch. When you know what the clutch does and why it causes the car to stall, you’ll know how to prevent it. Let’s take a look at the basics of a car’s clutch and following that, the reasons why you keep stalling your car.
1. Clutch Discs
Your car’s clutch essentially comprises of two circular discs that are made from friction material. The two clutch discs either press together or separate.
2. Clutch Location
The clutch sits between the engine and the gearbox. So you have the engine which then connects to the clutch, the clutch which connects to the gearbox, then on from the gearbox to the road wheels.
3. Clutch Discs Separating
When the driver presses the clutch pedal down to the floor, the clutch discs come apart from each other.
4. Clutch Discs Joining
When the driver releases the clutch pedal, the clutch discs come back together.
5. Mechanical Energy
The internal combustion engine burns fuel and converts the energy produced from from heat into mechanical energy. This mechanical energy rotates a shaft which then connects to one of the clutch discs.
The clutch disc that’s connected to the engine is always rotating, but when the driver presses down the clutch pedal, the clutch disc connected to the gearbox separates and stops rotating.
6. Mechanical Energy to the Wheels
When the clutch pedal is lifted and the clutch discs are joined, it forms a complete connection from the engine, then through the clutch, through the gears and ends up rotating the road wheels.
7. The Clutch is a Switch
The clutch is effectively a switch, so when the driver presses down the clutch pedal, the connection between the engine and the gearbox is broken, stopping the power from the engine from going to the gearbox and road wheels.
8. Why the Clutch is Necessary
The gearbox is a series of gears, or ‘cogs’ that rotate when connected to the engine. A car usually has 5 or 6 forward gears and 1 reverse gear. When selected, these gears need to be meshed with a shaft that leads to the road wheels.
It’s necessary that the clutch breaks the connection between the gearbox and the engine so that the gears (cogs) can slow down to match the speed of the cogs on the shaft that leads to the wheels. If they do this without slowing down, they will grind because of the different speeds that they’re rotating.
The break between the engine and gearbox is also necessary for stopping the car. If the break didn’t occur, the continuous connection from the engine to the road wheels means the wheels would try to rotate when the driver tries to stop the car. By forcing the car to stop with the footbrake and by not breaking the connection of power from the engine to the wheels (pressing the clutch down), the engine will stall.
9. Moving Off
Other than forgetting to press the clutch down just before stopping the car, another common reason for stalling is when trying to move off from a stationary position.
Remember that the clutch disc connected to the engine is always rotating and when the clutch pedal is pressed down, the clutch disc connected to the gears is stationary. The faster you bring up the clutch pedal, the faster the clutch discs join. As the clutch discs begin to join together, they need to do this slowly so that the engine has time to start pulling the weight of the car and gain momentum.
If you raise the clutch pedal too quickly, the discs also join quickly, not leaving enough time for the engine to pull the weight of the car. This is why you stall when moving off.
10. Clutch Bite Point
The clutch bite point is the moment when the two discs begin to join. As the rotating friction clutch disc connected to the engine begins to connect with the disc connected to the gearbox, the rotating disc begins to rotate the other.
The bite point is the critical point where you must raise the clutch pedal slowly. You can bring the clutch pedal up as quickly as you like before the bite point and when the car has momentum after moving off, you can then release the pedal all the way up. It’s just at the bite point are you need to be careful.
Hopefully with the use of these diagrams and the simple explanation of the clutch, you’ll have a basic understanding of what the clutch does and more importantly, why you keep stalling your car. We’ll now move onto some techniques to help prevent you from stalling.