Quote:
Originally Posted by Bob Bidonde
The taper on the rear axle is there to center the axle concentric with the brake drum assembly. Torque from the axle to the wheel is transferred by the shear key between the axle and the drum.
Applying a lot of nut tightening torque to the rear axle is not a good practice because:
>it increases the frictional force that resists removing the brake drum. In turn, this leads to the use of tools that may damage the axle's threads;
>it deforms the tapered joint, and eventually the brake drum rubs against the brake backing plate;
>it raises the tension stress in the axle at the inboard end of the taper where there is a stress riser due to the key slot and the abrupt change in the axle's cross section. This reduces the fatigue life of the axle.
It has been said many times that no torque wrenches were in use when the Model "A" was manufactured, so the assembly line worker was snugging the axle nut. The point is that there is no technical need to apply a torque more than is necessary to snug the brake drum onto the axle and engage the shear key in the process. Because someone publishes a book specifying 100 ft-lbs or more does not make the practice right.
My experience is that a snug with a wrench not exceeding 50 ft-lbs is adequate.
Okay you all. Fire away!
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The taper transmits the torque not the key. If the nut is not torqued properly the tapers will slip shearing the key. Once the key has sheared it ruins the tapers and they will not hold as designed.
Bill