The GM vehicles that come equipped with 4.8-liter engines are the GMC Sierra pickup and the GMC Yukon SUV. Both vehicles have the same belt replacement procedure. The belt operates all of the accessories on the front of the engine. These accessories include the alternator, the power steering pump, the air conditioner pump and the water pump. The belt routes around all of the accessory pulleys so that it can operate all of the accessories at the same time from one belt. Replace the belt if there is chafing or excessive cracking on the belt.
Open the hood and locate the belt routing diagram. This diagram is stamped to either the top of the fan shroud or the underside of the hood. You'll use the belt routing diagram to install the new belt around the accessory pulleys.
Locate the spring-loaded automatic belt tensioner on the front of the engine. The tensioner location on the GM 4.8-liter motors is located near the front center of the engine. The tensioner has a small pulley attached to one end. Use the bolt head in the center of the pulley to rotate the tensioner.
Remove the tension from the belt by rotating the tensioner pulley counterclockwise with the breaker bar and a metric socket. Then remove the belt from the underside of the pulley. Release the tensioner pulley and remove the breaker bar and socket.
Pull the belt out of each accessory pulley. Then pull the belt around each fan blade and out of the engine bay. Discard the old belt.
Route the new belt around the fan blades and around the accessory pulleys. Always start the routing process with the crankshaft pulley and end the routing process with the tensioner pulley. Use the belt routing diagram to route the belt around the other pulleys.
Rotate the tensioner with the breaker bar and socket again. Then slide the belt under the pulley and release the tensioner. The tensioner pulley will tighten the belt as it retracts. Look over the belt thoroughly to ensure that it is properly routed around the pulleys and that the belt is completely seated within all of the pulleys.
Crank the GM vehicle and let the motor run for about 15 seconds to completely seat the new belt into the grooves on each accessory pulley. Then turn the motor off and shut the hood.
