What symptom is typically associated with a bad viscous coupling in a vehicle?

A bad viscous coupling is typically associated with transfer case shudder at low speeds. This occurs because the viscous coupling is designed to distribute torque to the wheels as needed based on traction conditions. When the viscous coupling fails or becomes degraded, it can lead to uneven torque distribution, which results in shuddering or coupling engagement issues particularly noticeable at lower speeds. This symptom is a direct result of the coupling's inability to smoothly transfer power between the front and rear axles in response to changes in traction.

At high speeds, the effects of a failing viscous coupling may be less pronounced or noticeable compared to low speeds, which is why low-speed shuddering is more commonly reported in vehicles with this issue.