Mercedes Automatic Belt Tensioner Assembly - Febi 40446

Product Information

Accessories such as alternators, power steering pumps, water pumps, and A/C compressors are commonly powered by an accessory drive belt, also sometimes called a serpentine belt. For these to all function correctly, an accessory drive belt tensioner applies the proper amount of tension on the belt to keep it from slipping and ensure the entire system is running smoothly.

There are three main styles of accessory belt tensioners, the most popular being the “Automatic” tensioner. An automatic accessory drive belt tensioner is spring-loaded to maintain constant tension on the belt. Some European cars use a hydraulic-style tensioner, which is slightly more complicated but less prone to bouncing or vibrations if one of the accessories is not in top shape. Finally, a manual accessory drive belt tensioner uses a screw and an arm that needs to be manually adjusted. These are usually found on classic cars and need to be checked as part of regular maintenance.

When an automatic tensioner is failing, you will notice an abnormal amount of bouncing or vibration, usually in conjunction with a bad pulley bearing. Hydraulic tensioners will fail similarly, by losing their ability to damp the vibrations in the system and begin to bounce. Sometimes they can also leak, although the amount of fluid in a hydraulic tensioner is small, so it would be hard to detect. If your belt system is bouncing or wobbling due to slack in the tensioner, replace the tensioner and associated components to do a full belt service.

• Slack in the belt: If the accessory drive belt tensioner is going bad, you will notice the belt bounce and hop due to the inability of the tensioner to apply even constant pressure.
• Pulley Bearing Failure: Many accessory drive belt tensioners have a pulley integrated into the assembly. If the pulley bearing goes bad, it will cause inconsistent or excess resistance on the belt which will inhibit the ability of the tensioner to apply constant tension on the accessory drive belt
• False positives: Occasionally if another component is going bad within the accessory drive belt system, such as a power steering pump or A/C compressor, it can cause intermittent drag on the system that will appear as a faulty belt tensioner. If your belt is not running smoothly, check all the other accessories and idler pulleys to make sure they are smooth.

About Febi Bilstein

Ferdinand Bilstein’s febi brand is a global leader in the replacement parts market, known for offering high-quality alternatives to original equipment (OE) parts. With a range of over 50,000 technical replacement parts for passenger cars, light commercial vehicles, and trucks, febi ensures that consumers and professionals have access to reliable solutions for maintaining and repairing vehicles. The brand is committed to staying at the forefront of automotive technology, providing parts for hybrid, electric, and hydrogen-powered vehicles, and continuously expanding its product offerings to meet the demands of the evolving aftermarket. febi’s global presence spans over 170 countries, supported by advanced logistics centers that ensure fast delivery and product availability worldwide.

A strong focus on quality sets febi apart, as their products match or exceed OE standards, backed by rigorous quality control and in-house manufacturing capabilities. febi offers comprehensive repair solutions for all major vehicle brands and models, ensuring that critical parts are readily available for professional workshops. With a deep-rooted tradition in mobility and a future-oriented approach, febi is a trusted partner in keeping vehicles performing optimally, regardless of their powertrain or application.