Overrunning alternator pulleys are becoming increasingly popular on many late model passenger cars and light commercial vehicles due to increased alternator loads. As opposed to traditional solid pulleys, they allow the alternator to “free-wheel” or “overrun” every time the engine decelerates and, at the same time, dampen vibrations at the alternator.
They come in two types: one-way clutches (OWCs)
and overrunning alternator decouplers (OADs)
. While solving a similar problem, OWCs and OADs are quite different in how they function. OWCs rotate freely in one direction and lock immediately in the other direction; overrunning alternator decouplers (OADs) rotate freely in one direction and allow a small angular rotation in the other direction.
Like any other part, overrunning alternator pulleys don’t last forever, and technicians will be replacing more and more of them. As none of the pulley types are interchangeable, it is very important only to use the pulley type that the vehicle was originally equipped with
. So if a vehicle calls for a solid pulley, OWC or OAD, the same category of pulley must be installed. Also, proper tools need to be used to remove and install these pulleys
Furthermore, when an overrunning alternator pulley has reached the end of its service life Gates recommends that all wear parts are replaced at the same time to ensure the best long-term solution. It is also important to replace the overrunning alternator pulley when installing a new alternator.
HOW TO TEST IF AN OVERRUNNING ALTERNATOR PULLEY NEEDS REPLACEMENT?
Overrunning alternator pulleys do wear out, but this is not always visible to the naked eye. Follow these simple tests to identify an overrunning alternator pulley that is near failure:
If one of these tests fails, the overrunning alternator pulley should be replaced immediately:
Test 1 (left)
Hold the inner ring
Try to rotate the outer ring in the same direction as the belt would
The outer ring should not move. If it does, replace the overrunning alternator pulley
Test 2 (right)
Hold the inner ring.
Rotate the outer ring in the opposite direction as the belt would.
The outer ring should rotate. If it doesn’t, replace the overrunning alternator pulley.
Special test for overrunning alternator decouplers
OADs have an additional functionality and require special testing.
OADs should have a smooth spring feel in the drive direction and spin freely in the opposite direction. If not, the OAD requires replacement.
Note: The internal spring is strong and will require use of a wrench and special tool to properly diagnose the pulley.