There are a few different ways to adjust the drive belt or V-belt tension in a vehicle. The most popular used nowadays is a serpentine belt that connects to and activates every pulley in the engine. These serpentine belts require no tension adjustment as they incorporate an automatic belt tensioner. This type of tensioner has an internal preset spring and applies the correct amount of tension to the belt. Some older vehicles and some imports may use a combination of V-belts and serpentine belts in offset pulleys still controlled by the crankshaft pulley. Most often, there are belt tensioners on these vehicles that allow proper tension to be adjusted.
Open the bonnet and locate the drive belt system. Different types of vehicles use different methods to adjust the tension on the drive belts and the belt tension adjustment mechanism may be located in different areas. For example, some imports may require the removal of a front tire and wheel well splashguard to access the tensioner for the drive belts.
Determine where the tensioners are located for the individual belts and do what is necessary to access them. For example, lift the vehicle, remove the tire and splash shield (use the car lift, impact gun and a socket for the wheel) or locate the upper tensioner and determine what tools you need to adjust the tension.
Loosen the slotted alternator bracket if the vehicle is set up with this design. Some older vehicles would allow you to loosen the bolts on the alternator, including the bracket-retaining bolt. This would allow the alternator to move back and forth along the slot inside the bracket. To remove the belt or lessen the tension, the alternator would cock in a position to relieve the tension. To tighten the amount of tension, the alternator could be pried against the opposite pulleys and then be tightened down to increase the tension on the drive belt.
Locate the adjusters with adjuster bolts located near or on the alternator. This is a more common set up for vehicles that still use manual belt tensioners. A single bolt will be loosened counterclockwise (with a wrench or ratchet and socket). To remove the belt, a pulley or pulley would be loosened so the pulley would wobble enough to remove the belt once the bolt was loosened enough. To adjust the tension, turn the bolt clockwise to apply tension to the belt until the proper tension is achieved.
Test the proper tension on the belts. A general rule of thumb for the correct tightness is being able to twist a belt with a thumb and finger a 1/2 turn and feel resistance. If you can turn it more than a 1/2 turn, you do not have enough tension on the belt. If you cannot turn it a 1/2 turn, you have too much tension on the belt. Loose belts will result in premature belt wear caused by the belt slipping along the pulleys. This can also cause an alternator to be unable to replace a charge to the battery fully. There may also be a pronounced squeal from the belt during operation from the belt slipping. Over-tightened belts can cause internal damage to the bearings inside the pulleys. It can also cause overheating of the belts and premature wear.
Put the vehicle back together by replacing the components required to access the belt tensioners. To test, operate the vehicle for several minutes and shut it off. Touch the belts with your hand to check for proper tension and to see if the belts are hot.