How can I easily determine what rearend gear ratio I have?
Jack up the whole rear of the car. While turning the tire on full rotation, count the number of times the drive shaft turns. A chalk mark can be used as a reference point. If you have a posi rear, then the number of turns of the driveshaft (per single wheel rotation) is your gearing (i.e. 3.50 turns would be a 3.50 rear, or a 3.55 more likely). If you have an open (non-posi) rear, then you must multiply the number of driveshaft turns by 2 to get the gearing (i.e. 1.5 turns would be a 3.0 rear [1.5 * 2 = 3.0], or a 3.08 more likely). The reason for multipling by 2 is that in an open differential, the planitary gears cause the driveshaft to rotate half as fast as in a posi if only one tire is being rotated. Therefore, you must multiply the drive-shaft turns by 2 to get an accurate ratio, otherwise you must rotate one tire then the other (and not multiply). When one tire is not moving, the planitary gears are “walking” around the differential housing in the opposite direction causing the
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- How can I easily determine what rearend gear ratio I have?
