Thanks Dave. My case does have the bosses for the handbrake so that would indicate it is from a '35. The helical spline on the mainshaft was different than the gear from a '35, that is how I noticed the difference. I actually have two transmissions to work with so I guess I can just take the best parts from each. The new sliding gear fits on the mainshaft from the second transmission so that one must have an original mainshaft. The transmission that I pulled out of the car must have had a mainshaft and sliding gear which was replaced with one from a '39. The gear has the same number of teeth, the only difference is the angle of the helical spline. From what I can tell from my parts books and the two transmissions, the only difference between a '35 and '39 transmission is the angle of the helical spine on the mainshaft.

Can any one confirm or refute that?

(Curiouser and curiouser!)

If your transmission is truly from a 35, there are two bosses on the passenger side which are there to support the handbrake. These bosses are not present on a 37 trans as the brake lever is mounted to the floor. All the internal parts are the same through 37 in my experience.

The 38s changed the location of the handbrake to the dash so the trans has the brake attachment on the lower left.

39's used a different synchronizer. Possibly the low gear ratio is different.    I believe all the internal parts would transfer from one case to another.

I have also run into a difference in the helical spline so one reverse-low slider would not slide onto a particular mainshaft. To my eye, there was no discernable difference, but it would not fit.

All I can say is that while these transmissions are very similar, one has to be careful as to what does and does not fit.

I'm in the process of rebuilding what I thought was a 1935 transmission. The sliding gear was worn and I found a replacement. It didn't want to go on so I looked at the part number. The new part was from a '35, my old part was a '39. That means that the mainshaft and the sliding gear are different from those two years, though I can't find any other differences in my parts books.

One question I have is, the part number on the case is 631841. According to my parts book, it should be 631840. Is is possible I have a replacement transmission?

Can anyone shed any light on the differences between a '35 and a '39?