[Tom Endy]

The early cars had a different constructed ring & pinion and also a different gear ratio. See the attached article. There is also an early and late ring gear carrier. The later spider gears also have oil holes drilled in them.

The thickness of the gasket between the axle housings and the banjo was changed from .006 to .010 because of oil leaks. This required changing the depth of the bearing race stop in the axle housing and it has been a source of confusion over the years for people trying to overhaul a rear end when it comes to setting the carrier bearing pre-load.

During the Model A production run a number of changes were made to the four housings that comprise the rear end. However, they are all interchangeable and in the years since many surviving Model A's today have a hybrid rear end installed with a mix of housings from all the production years.
This is because after more than 90 years most rear ends have been apart numerous times and housing components replaced without regard to correct year.

In 1929 some, but not all, axle housings had the seams on the bottom. The 1928's had them on the side and they will face forward or aft depending which side you put them on. They can go on either side and the the correct orientation is strictly a judging standard issue. The later axle housings have the seams on the top.

The early banjos did not have support gussets around the torque tube flange and they were prone to crack. During an overhaul I generally replace an early banjo with a later, unless the car is going to be judged. The very late banjo's have the fill plug on the left of the center line. The idea is so you can peek in and see the condition of the gears. Good luck with that one.

The torque tubes are all interchangeable. There are slight differences in the shape over the production run.

The judging standards are the best source to determine the year of each housing component that makes up the rear end.

Tom Endy