As with most situations when dealing with fresh components, common sense goes a long way when breaking in a brand-new transmission. With new gears, blocker rings, and synchronizers, a new transmission will feel a bit tight at first, but Jeff Mortenson of Hurst says this is completely normal, and the trans will loosen up after 50-60 miles. "For the first 500 miles, you want to take it easy. As tempting as it may be, hold off on dumping the clutch or power shifting," he says. "The TKOs need to be filled with 2.65 quarts of a quality trans fluid like GM Synchromesh before you put any street miles on them. The fluid is designed to last the life of the transmission, so you don't have to drain it after the break-in period."