I had an alternator decoupler pulley (ADP) failure, a product I had never heard of until today. I did not locate a thread addressing these pulleys; so, I thought I'd start one to inform/help others. Most of the info below is from the Gates/Napa website. I found their website and youtube videos very informative.
There are currently two types of ADP pulleys: Alternator Decoupler (OAD) Pulleys and One-Way Clutch (OWC) Pulleys. Toyota products use the OAD type.
Essentially, these pulleys have a clutch-type mechanism inside the pulley that allows the pulley to free-spin when de-accelerating. It's suppose to smooth out engine vibration and "improve the performance and efficiency of car and light truck engines." Sounds hokey to me; it's just another auto part susceptible to failure and a profit maker for the stealerships, but that's just my
It's fairly easy to identify ADP pulleys. The end of the pulley will have a cap or similar cover to protect the innards. Under the cap, it will look like the one on the right:
Diagnosing ADP pulley Failure
--If you hear a buzzing noise immediately following engine shutdown, the bearings in the pulley have failed and it will need to be replaced. In this situation, if you turn the pulley by hand, you may feel grinding or roughness.
--When you hold the alternator still and the pulley spins in both directions, it should be replaced. The pulley should spin freely in only one direction and engage the alternator in the other.
--If the pulley won't spin freely in either direction you’ll need to replace it. You'll experience increased tensioner movement or belt slap when the engine is operating with a seized pulley. [The tensioner may have to be replaced, for a seized bearing puts excessive strain on the tensioner.]
--There are metal shavings inside the pulley.
My pulley failed the second and forth test. When I removed the cap, the innards were full of a fine rusty dust.
Removing the Pulley
Needless to say, removing these special pulleys require the purchase of new tools. They range in price from $40-$120.
When to Replace?
As preventive maintenance replace the pulley when rebuilding the alternator and/or when replacing the serpentine belt.
Some Toyota models with these pulleys:
4Runner 2.7L, 4.0L
Avalon, Camry, Highlander, RAV4, Sienna, Venza 3.5
Celica, Corolla, Matrix 1.8
Lexus ES350, GS350, IS250, RX350 2.5 & 3.5
Scion XB, XD 2.4