Drive Belts: The Auxiliary Belt That Runs Everything Else

The drive belt — also called the auxiliary belt, accessory belt or serpentine belt — runs at the front of the engine and drives the alternator, water pump (on some engines), air-con compressor and power steering pump (on hydraulic-PAS cars). It’s separate from the timing belt and has its own tensioner and idler pulleys.

How the belt is designed

Most modern drive belts are multi-rib designs — typically 6 or 7 ribs running on grooved pulleys. The multi-rib design transmits high torque without slipping and stays quiet. Older designs used V-belts (single ribbed cross-section) which are still found on some applications but largely superseded.

The belt material is reinforced rubber, similar to timing belts but optimised for the lower-precision auxiliary drive duty. Service life is typically 60,000-100,000 miles.

Symptoms of belt failure

Chirping or squealing on cold start, fading as the engine warms. Whining or whistling that varies with engine speed (usually a worn idler bearing rather than the belt itself). Visible cracks across the belt teeth. Glossy rubbing patches on one belt edge (the belt is running misaligned, often due to a worn tensioner). Charging system warning light if the belt snaps and the alternator stops spinning.

Replacement

Drive belt replacement is straightforward — relax the tensioner, slip the old belt off, route the new belt around all the pulleys in the correct pattern (an engine bay sticker often shows the routing). Replace the tensioner at the same time if the old one shows wear; idler pulleys should also be replaced if their bearings whine. The whole job is usually under an hour on most cars.

Brand

Continental ContiTech, Gates, Dayco are the dominant OE belt suppliers. The aftermarket parts are identical to OE specification. Avoid no-name belts — the rubber compound and rib geometry vary more than you’d think.

Find drive belts for your engine on the Drive Belt collection. A small service item that affects most of the front-of-engine accessories.