Propeller Shaft Rotational Speed

WARNING: This page is about a different car, the 2003 Pontiac Aztek and 2003 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.

The rear differential assembly is designed to provide on-demand drive torque to the rear tire and wheel assemblies as needed. The differential incorporates clutch packs that are fed differential gear lubricant by gerotor pumps under certain conditions to provide the needed drive torque to the rear wheels. The rear differential assembly is designed to allow varying amounts of slip between the amount of input torque coming from the transfer case through the propeller shaft, and the amount of torque being delivered to the rear tire and wheel assemblies.

The propeller shaft is rotated by the transfer case during any movement of the vehicle - even when the all-wheel drive (AWD) system is disabled. The transfer case is attached directly to the transaxle and incorporates functions of the transaxle extension housing. The transfer case operates using the final drive ratio of the transaxle output shafts as input to the case. The transfer case then modifies the transmission output ratio very slightly for the propeller shaft by a factor of 1.013:1. As a result, the propeller shaft then rotates at approximately the same speed as the front tire and wheel assemblies.

If the (first-order) rotational speed of the tires is determined to be 13 Hz, then the (first-order) rotational speed of the propeller shaft would also be 13 Hz. The slight ratio change that occurs through the transfer case will have little affect on the propeller shaft rotational speed:

13 Hz X 1.013 transfer case (output) ratio = 13.169 Hz (still rounded to 13 Hz) first-order propeller shaft rotation related disturbance

The propeller shaft uses front and rear constant-velocity (CV) joints. Each CV joint uses a 6-ball bearing design. It would be possible to have a sixth-order propeller shaft rotational disturbance.

To compute a sixth-order propeller shaft rotation related disturbance, multiply the first order rotational speed of the propeller shaft by the order number of 6:

13 Hz X 6 (for sixth order) = 78 Hz sixth-order propeller shaft rotation related disturbance

Using the non-rounded numbers, you would derive an answer of 79 Hz for sixth-order propeller shaft rotation.