The hardest part of working on a transmission is preventing the flywheel from turning while connecting or disconnecting it from the engine block. Each manufacturer makes its own custom flywheel lock tool, but they can be very expensive. Every home mechanic can lock the flywheel on a car without special tools by understanding one basic fact about the flywheel. The bolts that hold the flywheel in place will also turn with the flywheel. If you grab the bolt and hold it in one place, the flywheel cannot turn.
Disconnect the negative cable from the battery using a socket wrench to loosen the locknut. Pull the cable off the terminal post.
Disconnect the wire from the positive terminal on the battery from the starter by removing the locknut with a box wrench from the starter post and pulling the wire off.
Remove the bolts holding the flywheel cover in place with a socket wrench and lift the flywheel cover off to expose the flywheel and engine studs.
Shift the car into neutral.
Turn the flywheel by putting a box wrench on one of the bolt heads holding the flywheel in place and pushing or pulling on it until the opposite end of the wrench can reach one of the engine studs protruding from the engine block.
Fit a double ended wrench onto the flywheel so one end is locked onto a flywheel bolt and the other end is over the engine stud.
Turn the flywheel (using a box wrench on a free bolt) until it cannot move any further because it has reached the full length of the wrench locking it to the stud.
Slip rubber o-rings over the ends of both bolts to prevent the heads from stripping when the flywheel strains against the wrench.
Do not work on the flywheel with the starter connected or the engine could turn over and cause serious injury.