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Posted by Clint Dixon on Saturday, July 26, 2008 at 21:58:00 :
In Reply to: Re: Got to be about 2 1/2, or about 3 if 5.83. posted by Vaughn on Saturday, July 26, 2008 at 21:25:19 :
If one has both rear wheels off of the ground, and can spin both together as one (two-wheel method), for one complete revolution, the driveshaft will turn 5.83 revolutions (or just a little less than 6) if the truck has 5.83:1 gearing. The driveshaft will turn 4.89 revolutions (or just a little less than 5) if the truck has 4.89:1 gearing. These ratios work because all of the pinion gears and side gears in the differential case remain stationary when both wheels turn together.
Lifting only on wheel off of the ground (one-wheel method) for the test will work just as well assuming there is not a locking differential installed in the truck. By using the one-wheel method, one has to take into account that all of the pinion gears in the differential case will be spinning, in effect absorbing half of the motion, and the driveshaft will rotate exactly half of the revolutions of the two-wheel method.
One revolution of the wheel (one-wheel method) will turn the driveshaft 2.92 revolutions (or just a little less than 3) if the truck has 5.83:1 gearing. One revolution of the wheel will turn the driveshaft 2.45 revolutions (or just a little less than 2-1/2) if the truck has 4.89:1 gearing.
Excessive wear in any of the differential gears or components can change the number of driveshaft revolutions slightly. One must be sure to turn the driveshaft against the direction of rotation to take up backlash before counting revolutions.
APB correctly determined that he has 4.89:1 gearing.
Junior
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