Drive Belts

Many of the accessory systems in a car are driven by nothing more than a pulley and one or more car engine drive belts. Before the introduction of the single serpentine belt by Ford in 1979, multiple belts were commonly used. A serpentine belt has many advantages over multiple belts, including reduced slippage and longer service life. Belts should be replaced regularly to avoid failures that can result in damage to the engine and accessory systems. Installing new belts is a quick and simple task that can be done at home by most people.

Car engine drive belts power most of the accessory systems from the crankshaft pulley. They turn the alternator to provide electrical power for charging the battery, and they turn the pump that generates pressure for the power steering system. They may also turn the water pump for the cooling system, but in many cars this is done by the timing belt or chain. Another part of the cooling system that is turned by the belts is the radiator fan. The belts also power non-essential systems, such as the compressor pump for the air conditioner.

The old method of powering accessory systems relied on multiple car engine drive belts. These v-belts were long and narrow, with a triangular cross-section that gave them their name. They were made from natural rubber and had minimal reinforcement, which made them prone to stretching and slipping. It also meant that they had a short service life and would frequently break. One advantage of using multiple belts is that other systems would keep working if one belt broke. But this was also a disadvantage because it was hard to tell if a belt had broken without opening the hood.

The modern system replaced all those car engine drive belts with a single serpentine belt. It is called a serpentine belt because of the way it snakes around the many pulleys of the accessory systems. The belt is made from synthetic rubber and has many strands running through it for reinforcement. This allows the belt to support a higher tension loading than the old v-belts, reducing slippage and improving efficiency. One side of the serpentine belt has many groves on it for driving the pulleys while the other side is flat.

A serpentine belt also passes over other pulleys that are not connected to accessory systems. The crankshaft pulley is located at the base of the engine and is the only pulley that provides torque for driving the belt. A spring-loaded tension pulley stops the belt from jumping off the other pulleys as the engine speed increases and decreases. There may also be one or two idler pulleys to change the direction of the belt so that it can grip more of the pulley ahead of it. The flat surface of the belt passes over the idler and tensioner pulleys, while the grooved surface passes over the rest.

It makes sense to replace many car engine drive belts with one serpentine belt. Along with the greater efficiency and reduced slippage from using one belt with a higher tension, there is also less loading on the engine. It is easier to adjust one belt instead of many belts and it does not need to be adjusted as much because it is less prone to stretching. The longer service life of the serpentine belt means it is less likely to fail and cause damage to the engine and accessory systems. It is also easier to spot a serpentine belt failure because all the system stops working at once.

Replacing a serpentine belt is a simple task that takes about one hour and can be done at home. The tensioner pulley needs to be moved away so that the belt is slack enough to be removed from the other pulleys. The tensioner can either be held back with string, or it can be moved away by loosening the bolts holding the bracket. Before removing the belt, it might be wise to make a diagram of the path it takes. Place the new belt around the pulleys and adjust the tensioner so that the belt has the correct amount of slackness, as noted in the service manual.

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