Model A & B

Ford Garage

Driveshaft Differences

Shown below is a comparison between the 1928-31 Model A Ford driveshaft and the 1932 Model B driveshaft assembly.

Many parts in the Model A and B rear axle assembly are common and interchangeable including the differential housing (banjo), axle shafts, bearings, ring and pinion, spider and gears, and differential carrier halves.

The torque tubes and driveshafts are quite different however.

Pictured above is a Model A driveshaft on top and a Model B driveshaft below it.

The Model A driveshaft has an overall length of 54 inches. The Model B driveshaft has an overall length of 56-1/2 inches and a diameter of 1-3/4 inches.

The Model A driveshaft is a solid one-piece steel shaft, in comparison to the Model B shaft which is a three-piece electric welded assembly.

This close-up of the pinion gear ends of the two shafts clearly shows the Model B construction of a forged and machined taper end, welded to a tubular center section.

Increased length of a rotating shaft creates more whip and shorter fatigue life, all else being equal in design. The longer Model B design length drove a need for a change in construction compared to a Model A shaft.

The tubular construction of the Model B driveshaft stiffens the shaft and raises the natural frequency of the shaft. This allows it to rotate at higher rpm with reduced whipping and without fatigue failure, and to tolerate more mass imbalance of the rotating shaft, in contrast to the solid Model A shaft.

This close-up above of the front splined ends of the shaft also shows the welded tubular construction of the Model B, as well as the increased length of the Model B driveshaft.

The construction was likely not changed for any ultimate strength reasons, as the ends are unchanged from the Model A design. The ends remain the weakest link, strengthwise, though adequate for the application.

It is most likely that Ford changed to the tubular construction to raise the stiffness and frequency for the increased length without increasing mass, to reduce the whip, and to enable higher allowable rpm of the shaft.

Shown above is some detail of the spline design.


April 2004