While most motorcycle manufacturers opt to house the engine and transmission together, Harley-Davidson uses a two-part engine and transmission system to power their motorcycles. The engine’s power output is transferred to the transmission through the primary chain, housed behind an oil-filled cover on the left side of the motorcycle. Just as the engine’s oil supply works to reduce internal friction, the fluid within the primary chaincase reduces wear on the chain and the transmission’s clutch plates. The primary fluid must be changed every 5,000 miles to ensure that your Harley-Davidson is ready to ride when you are.
Take your Softail for a brief, 10-minute ride. Shift through all five gears, six for newer Softail models, while riding at a moderate pace. Park the motorcycle on its side stand, once you return, and let it cool for 10 minutes.