Dayco® No Slack™ Automatic Belt Tensioner is designed to maintain constant tension on serpentine belt drives. The serpentine belt drives consist of a single belt that powers most, if not all, of the engine's accessories. To maintain the proper tension throughout the drive, an automatic, spring-loaded tensioner is incorporated into the drive system geometry.

Dayco's Automatic Belt Tensioner features a patented "flat spring" design that's engineered to provide less operating range variations in tension. This reduces the risk of premature accessory bearing failure due to high tension when a new belt is installed. It also lessens the risk of belt squeal and slippage, or poor accessory performance caused by low tension after the belt begins to stretch and wear. A Teflon® strip wound within the spring resists abrasion. The flat spring itself is coated to resist rust.

Other superior design features include a steel locator pin (where the application demands). A heavy-duty cast aluminium spring case resists cracking and fatigue. The heavy-duty cast aluminium arm offers additional strength and less distortion. An aluminium retainer ring locks the spring case and arm together, and seals against corrosion. A steel pivot tube (where the application demands) provides additional strength for critical torque requirements. A thermoplastic rubber spring slot plug keeps out harmful contaminants. The lubricated nylon pivot tube bushing and spring bushing promote quieter performance. A rubber O ring seals against dust and grime. The zinc-coated mounting bolt resists rust, and is concentric for a more even degree of constant tension.

In order to meet OEM performance standards, Dayco Automatic Tensioners come with either a glass-filled polymer (plastic) or steel pulley that features a dust cover to protect against contaminants.