Model A & B

Drive Shaft Differences

Shown below is a comparison between the 1928-31 Model A Ford drive shaft and the 1932 Model B drive shaft 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 drive shafts are quite different however.

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

The Model A drive shaft has an overall length of 54 inches, and a diameter of 1-1/64 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 drive shaft is a solid one-piece steel shaft, in comparison to the Model B shaft which is a three-piece electric welded assembly.

The early 1928 Model A drive shaft (not shown) has a threaded section at the rear for securing the differential pinion gear bearing lock nuts directly to the shaft, not to the pinion gear.

The threads and nuts were moved from the drive shaft onto the pinion gear itself later in 1928, and the lock nut sizes were enlarged to fit the pinion gear.

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 drive shaft 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.

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

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, strength-wise, 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, in order to reduce the whip, and to enable higher allowable rpm of the shaft.

Shown above are some details of the spline design.

More related information on Ford Garage:

For more Model A & B related information, use the Site Search box at the top or bottom of this page.
Model B Drive Shaft Removal Methods
Model A & B Original 5-Z-1833 and 5-Z-2065 Pinion Nut Wrenches
Model A & B Pinion Gear Race Removal Methods
Model A & B Rear Axle Gear Ratios
Model 40 & 46 Engine Rear Support Mount

April 2004