Transmission main shaft issue

[Tom Endy]

There are a number of traps set up in the Model A transmission for the modern hobbyist. The main shaft has several. The early main shaft has a flat looking washer that appears to be permanently attached to the front of the shaft. The later ones have a round "key ring" looking spacer that is removable. Both shafts are interchangeable.

However, I have seen people put a removable spacer over the fixed one. This will not work and will bind the transmission. The spacer is there to keep the front roller bearing in position. I always replace the later "key ring" spacers with a new one as they are usually worn flat in the front. I have also found the long roller bearing in the front position, this also locks up the transmission and pours oil out the front.

Ford issued a service bulletin back in the day dictating that when replacing the main shaft the two slider gears should be replaced as they are sold as a matched set for tighter clearance. The purpose being to prevent jumping out of gear. A good way increase parts sale and certainly not available today from modern suppliers. There is a whole shopping list of reasons a Model A transmission will jump out of gear.

The bearing surface on the main shaft can be machined down and a hardened sleeve pressed on to restore the surface, as can the nose on the input shaft. When replacing the main shaft and the two slider gears you have to attempt to achieve a tight clearance match. When doing so I select the match from a collection of parts I have. Some I have found to a terrible match, more than likely from reproduction or after market parts.

I also ran into a situation where I had an original input shaft and an original main shaft but they would not fit together. The front end of the main shaft bottomed on the inside free area past the roller bearing and bound up the transmission. They must have been manufactured at different factories. I was able to salvage them by grinding material off the front end of the main shaft.

Ford also changed the diameter of the oil baffles on both the early and late input and main shafts. If you install the late baffles in an early housing you will bind up the transmission, Vendors today only sell the later larger oil baffle.

There are several articles available about transmission overhaul, one in particular speaks to the traps in a transmission Henry laid for the next hundred years of Model A hobbyist.

Go to the Santa Anita A's of Arcadia, California web site at santaanitaas.org. On the home page put your cursor on "Technical Reference" and my name will appear below, click on it, and it will bring up a technical library. Scroll to the section of transmissions.

The articles are pdf files and you are welcome to download, save, and print out. The articles are there for the benefit of the Model A hobby and are not restricted in any way.

Tom Endy

[tomii]

Originally Posted by Tom Endy

....

Ford also changed the diameter of the oil baffles on both the early and late input and main shafts. If you install the late baffles in an early housing you will bind up the transmission, Vendors today only sell the later larger oil baffle.

...

Tom Endy

And THAT answered my own question of why the danged thing was hung up as soon as I'd tighten any bots (clearly, something was binding)


Some careful work on a grinding wheel fixed the problem.