However, there's one big gotcha - almost always one shaft is dramatically shorter than the other. In my own GM Dana 60, the long side shaft is 35" long, or about 50% longer than the 18" short side shaft. The problem with this becomes evident when we recall once agaibn our friend the angular deflection equation (math is soooo cool
alpha=[584(T)(l) ] / D^4 * G
Where:
alpha = the torsional deflection in degrees (how much it twists)
T = Torsional or twisting moment in inch pounds (torque or load placed on the axle)
l = length of the shaft in inches
D = diameter of shaft in inches
G= torsional modulus of elasticity (a constant for all steel shafts at 11,500,000 psi )
In my front axle in any given "all wheels driving" sitaution, for each shaft G and T are equal, or about equal, and l is quite different: meaning that if D is constant between the 2 shafts, the longer shaft will twist more than the short. This will normally allow the energy to be dissapated better in the longer, greater twisting shaft than in the short shaft - this explains why quite often we see more broken short side axles than long.