Certain Toyota AWD models suffer from differential bearing noise. Mike Riley explores these issues in this episode, covering diagnostics.
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Toyota uses a rather unique rear differential design which involves not only a viscous coupling but also an electromagnetic coupler. Model variations determine the basic design of the viscous coupling unit. Vehicle applications such as the RAV 4 use a design in which the electromagnetic coupler is attached to the differential, separate from the viscous coupling.
A Siena van for instance, has the electromagnetic coupler contained within the viscous coupling assembly although ultimately both designs operate in the same way.
Due to the fact, that the large bearing which supports the viscous coupling is somewhat exposed to the elements the bearing can fail over time. The upgrade provided by Toyota in effect adds a large seal to the assembly to avoid this problem. A TSB (T-SB-0080-13R1) was issued by Toyota addressing this failure along with product and repair information.
Note: Always refer to OE product and technical information
