"The simplest procedure can be done in your garage in a few seconds. It assumes that the brakes are working, that the clutch hydraulics are working, the starter motor works, and that the battery is charged. (I suppose it also rashly assumes that you have two feet and at least one hand). Sit in the driver's seat. Pump the brake pedal a couple of times and hold the brakes on firmly with your right foot. Depress the clutch pedal fully with your left foot. Put the transmission in 4th gear (least likely to drive the car away), and engage the starter for about one second. If you're lucky the torque from the starter motor may break the flywheel free from the clutch disk, and the engine will crank over normally. If that doesn't work in the first try or two, move on to Plan B.
The rest of these procedures require some open running space on a totally vacant street or empty parking lot. Put the transmission in neutral, start the engine and allow it to run up to normal running temperature. Give it a tune up if necessary so it runs reasonably well. Switch engine off, and take the car to a safe open space (preferably paved). You may expect the car to lurch forward during this operation, so be sure there is no one and nothing around the car. In fact for this procedure you will actually be driving the car.
With car stationary, engine off and parking brake off, depress the clutch and select 1st gear. Hold the throttle down slightly (1/2" or so), and start the engine. The car should jerk lurch forward and gradually pick up speed until the engine is running at or above idle speed. Run it up to about 2500 rpm, which will be about 10 mph in 1st gear. This engine speed is the speed at which a stock engine will develop near maximum torque. With the clutch pedal still fully depressed, and running at around 2500 rpm, alternate the throttle pedal between full down and full up position. This will alternately apply full engine driving torque and full engine braking torque (coasting down with no throttle) to the clutch, and with a little luck this may be sufficient to break the bond to free the clutch disk. Assuming that it will work, you should be prepared to get your foot off the throttle before you over-rev the engine, and get on the brakes to bring the car to a stop. If this does not work then take the car to a convenient open work space, kill the engine, and proceed to Plan C.
With the engine and parking brake off and the vehicle pointed in a safe direction, use a hydraulic floor jack with a long handle (not a bottle jack). Place the jack under the center differential housing of the rear axle to lift both rear wheels so they are clear of the ground by about two inches. Get into the car and confirm that there are no obstacles or people in front of the vehicle. With engine and parking brake still off, shift the transmission into 4th gear (least driving torque at rear wheels when full engine torque is applied up font). Start the engine and throttled up to a constant tachometer reading of about 1500 rpm. This puts a substantial amount of energy into the rotating engine and flywheel. Depresses the clutch pedal and keep it depressed, then apply the brakes firmly and suddenly. The inertia of the engine and flywheel will apply a very large torque to the stuck clutch, limited only by how fast and how hard you can apply the brakes. If this works the clutch will disengage and the engine will continue running when the brakes are applied. Then set the parking brake, remove the jack, and you can drive the car normally. If this doesn't work it will kill the engine. If it still doesn't work after a few tries, proceed to Plan D.
This procedure is a little more dramatic, and it requires an assistant. As in the prior method, raise the rear wheels a couple inches off the ground with a hydraulic floor jack. Leave the jack handle extending to the rear, and very close to the ground. The driver gets in the car, selects 4th gear (least torque at rear wheels), and starts the engine. This time run the engine up to about 2500 RPM, so it may develop good flywheel energy and maximum torque (if you hit full throttle). On pre-arranged signal, the assistant then snaps the jack hydraulic valve full open to drop the car suddenly to the ground. If all goes well the tires will suddenly stop turning while the engine keeps running, and the clutch bond will have been broken. If it doesn't work, the tires will squeak once, the car will lurch forward a bit, and it will kill the engine.
The functional difference between this method and simple application of the brakes is that the full weight of the car is brought to bear on the tires to provide sudden resistance on the driveshaft, which may allow more applied torque than you get by using the brakes. This is not guaranteed, as with well functioning brakes you should be able to lock it up and skid the tires when the car is moving. However, dropping the running car onto the rear tires may apply the torque more suddenly than you might do with the brakes, so the resulting shock to the clutch might be greater. Also, in addition to the torque you get from inertia of the engine and flywheel, if the partners in this venture can time things right, you might hit full throttle just at the same time that the tires come into contact with the ground. This will apply full engine torque to the clutch in addition to the torque resulting from sudden deceleration of the flywheel. As with the prior method you should assume that it will work, and be ready to get your foot off the throttle before over-revving the engine when it breaks loose.
If that doesn't work, take the car back to the garage and proceed with Plan E. Remove engine from car, remove clutch pressure plate and clutch disk from flywheel. Use large pry bar if necessary to pull pressure plate free. Use a solid punch (or chisel) and heavy hammer on the edge of the clutch disk if necessary to separate it from the flywheel. This would of course be the most extreme and least convenient of all, so lets hope one of the prior plans works first so you don't have to pull the engine."
