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How to Tell when an Idler or Tensioner Pulley Needs to be Replaced

Top Eight Pulley Warning Signs

Did you know that one of the most common causes of serpentine belt failure is a pulley with worn bearings? That’s because a pulley’s job is to maintain proper tension and alignment on the drive belt. So, how can you tell if a pulley has gone bad? Read on.

The Difference Between Idler Pulleys and Tensioner Pulleys

There are two basic pulley types – the idler pulley and the tensioner pulley – but their role and design are similar.

Tensioner Pulley

A tensioner pulley uses a spring loaded arm or a hydraulic actuator to apply the proper pressure and help keep the belt tensioned and aligned. On a drive belt system, the tensioner pulley is spring loaded to maintain proper tension and alignment of the serpentine belt.

Idler Pulley

The idler pulley is bolted on the engine and serves as a guide to wrap the timing belt in the correct direction.

Eight Bad Pulley Symptoms

We suggest technicians change a pulley whenever a timing belt or serpentine belt is changed and vice versa, but there are eight key warning signs to look out for when a pulley goes bad:

  1. Rock – Rock the pulley back and forth. There should be no movement or play from side to side.
  2. Misalignment – Misaligned pulleys will cause belt chirp noise problems and are caused by worn bearings.
  3. Cracked or Broken Pulley – Check for obvious physical damage.
  4. Free Spinning Pulley – Spin the pulley with your fingers. Does it spin more than 1-2 revolutions? If it does, the cause is a lack of grease in the bearing, a sign it will fail soon.
  5. Seized Bearings – An indication that the pulley will lock up.
  6. Discoloration – This can be caused by intermittent seizure of the pulley bearing or a bad tensioner, causing belt slip.
  7. Surface Build Up – A key indication of a worn out tensioner causing belt slip.
  8. Excessive Wear – Common on vehicles operated in dusty environments.

Dayco Idler and Tensioner Pulleys

Dayco’s idler and tensioner pulleys come in different materials – from stamped and forged steel to plastic and powdered metal. Ultimately each one is designed based on the OE recommendations. We include premium pre-lubricated bearings and high temperature seals to ensure peak performance, which is the most critical element of a pulley’s service life.

For more on pulleys and their role in the front end drive system, watch this video.