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A push start is a procedure for starting a car or other vehicle that has a dead or undercharged battery. The procedure generally involves pushing a vehicle until it reaches a given speed, then using the inertia of the vehicle’s movement to provide the power needed to start it. Only vehicles with internal-combustion engines and manual transmissions can benefit from a push start.
Normally, a battery starts a car. When the ignition switch is turned to start the vehicle, power passes from the battery to the starter, a small but powerful electric motor mounted at the rear of the engine. When the starter receives power from the battery, it extends a small drive shaft that meshes with the gear teeth on the starter ring gear, which is part of the engine’s flywheel. The starter then turns.
As the starter operates, it turns the engine’s flywheel. This causes the engine’s camshaft to rotate, which cycles all the internal components of the engine. It also turns the fan belts and other devices connected to the engine. Included in these devices is the vehicle’s alternator, which generates the electrical power needed by the engine to run.
Once the starter is turning the engine fast enough for the alternator to generate sufficient power, the spark plugs fire, igniting the fuel in the engine’s cylinders. At this point, the engine starts. The ignition key is then released, the starter ceases to turn, the starter drive shaft retracts, and the engine remains running under its own power.
If a car’s battery is dead, the vehicle will not start. This is because there is no power to engage and operate the starter. If the vehicle has a manual transmission, however, it can be started by executing a push start.
Accomplishing a push start on a car is a simple procedure. First, a person must be in the driver’s seat. He or she must then turn the ignition to the on rather than start position, place the transmission in neutral, release all brakes, and press and hold the clutch in.
Next, another person or people, or another vehicle, pushes the car to a speed between 5 and 10 miles per hour. Once the appropriate speed is reached, the person in the car releases the clutch, and the vehicle should start. This happens because as the vehicle moves, it rotates the wheels, which in turn, rotate the drive shaft and the components of the transmission.
Once the clutch is released, the rotational energy of the transmission is transferred to the flywheel of the engine. At this point, the energy transferred from the transmission does exactly the same work as the starter. It turns the engine, which turns the alternator, powers the spark plugs, ignites the cylinders, and starts the engine.
When I was a kid, I had no idea you could push start a car if it wouldn't start the usual way. My dad told me and my brother to get out and push the family car while he popped the clutch, and I didn't understand what was about to happen. We were scared to death the first time the engine started, so we stopped pushing and the car stalled out. The next time, we got it right.
In a way, I'm glad you can't do that with most cars these days. It was a tricky and dangerous maneuver sometimes. My dad would run out of road before the car started, or we'd slip on the ice and snow during winter months. There was no completely safe way to push start a car, either for the driver or the pushers.
I remember having to help push start a friend's 1971 Volkwagen van a few times. I never volunteered to be the driver, since I wasn't that good with manual transmissions. Three of us would get behind the van and start pushing it with everything we had. The driver would decide when it was time to pop the clutch.
When you push start a car, there's a moment when the car will lose some forward momentum, so you can't stop pushing from behind when the driver lets off the clutch. The first attempt may end in a stall, too. Our main problem was having enough free space in front of us to get the car up to speed.
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