Posted by Clint Dixon [74.206.63.42] on Saturday, July 27, 2013 at 21:27:48 :
In Reply to: Re: Let me explain a little further posted by Jerry in Idaho [24.223.94.244] on Saturday, July 27, 2013 at 20:42:36 :
It is common to find a factory Spicer 44 under the front of a truck and a Spicer 60 under the rear - or in the case of some Fords, a Spicer 44 in the front and a Ford 9-inch in the rear.
The problem is found in involute gear cutting which is an exact and complicated process - a science if you will. Each axle has a specific ring gear diameter determined by the housing size. The ring gear in a Spicer 44 is larger in diameter than that in a Spicer 30 because the housing and most of the rest of the components are larger for more load capacity. The Spicer 60 ring is larger in diameter than the 44. The 70 has a larger ring than the 60, etc.
Then there is the tooth size, determined in part, by the size of the pinion and how many teeth can successfully be cut on it. It is not always possible, given these variables, to get exactly the same tooth count and resulting ratio in a differential that uses an 8-inch ring as in a differential that uses a 9-inch ring.
So, they got the closest they could. That Jeep may have a 4.11 ration in the rear axle and a 4.10 in the front because the front axle is lighter duty and with physically smaller components than the heavier duty one in the rear (which theoretically carries more weight, endures more torque, and takes more punishment than the front). So the vehicles with imperfectly matched ratios do not crab walk down the road, the higher ratio will be found in the front causing the front to want to pull the rear rather the rear always trying to pass the front.
Dodge was kind of odd really in that they built both the front and rear axles the same. The result was that the pumpkins and all the internal components are interchangeable and with the exact same ratio - really the best of the best.
The only reason that the front is rated at only 3,750 lb. capacity while the rear is rated at 6,500 lb. capacity is because the addition of steering knuckles and a flex withing the drive to the hubs weakens the overall assembly. Fortunately, that flex is a constant velocity (Tracta)joint, which although it was not the strongest constant velocity joint ever made, was way better than the simply u-joint found in modern vehicles.
One way to find out if the Tracta joints are getting warn is to put the truck in fist gear low range with the wheels turn to full lock left or right, and drive around in circles in a grassy field. Modern vehicles with common u-joints in the knuckles will lurch even when they are new. The WDX-WM300 Power-Wagon with constant velocity Tracta joints will not lurch unless the joint or the bushings are worn - a tire or two will slip and tear up sod, but there will be no lurching.
Junior
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