Any verifiable difference in the late/early transmissions?

[Punkskalar]

So I've been messing with transmissions this week, for fun, and to see WHY the 5th Gear OD from MikesXS won't work in the early transmissions (as stated by MikesXS). I've taken it for granted in the past, and supposedly the gears are "cut different" seems to be the popular opinion.

BUT, I've got a 72 model transmission in front of me, and an 80' model transmission.

Side by side, the 5th gears are identical in tooth cut, with the later gear having narrower teeth than the early... The narrower teeth are due to a relief cut on the backide of the gear, which appear to be due to the extra thickness of the gear next to it on the later model transmissions.

So I have swapped the MikesXS gear onto the early transmission, and have run it through all the gears in the cases... The narrower teeth seem to have the same amount of tooth contact as stock, and the extra clearance would obviously not be a problem at all. There is seemingly no reason it won't work....

 

[xstra]

Look at the shaft splines. You can get it all together but the fit isnt perfect. As an aside, apparently the gear hardness is also different(?)

 

[Punkskalar]

Look at the shaft splines. You can get it all together but the fit isnt perfect. As an aside, apparently the gear hardness is also different(?)

The shaft splines are a bit different, but the 5th OD is not splined, and has the same ID as the early gear's ID. So the splines should play no role in the 5th gear swap... That said, the shafts on both models are the same OD as well...

I'm still sitting here doing some measurements... There are a few things different, but so far, I see no reason it will not work...

 

[XSLeo]

The way the gears ride on the splines is what changed. I don't recall which was early and late. One way the gears rode on the top of the splines, the other way the gears rode in the bottom of the groves between the splines.
How this effects a gear without splines I'm not sure. When new, the diameter of the splines may have been enough different that the gears won't swap. After 35 years of wear they might.
Leo

 

[CoastsideXS650]

Any word on that 5th overdrive gear in an early transmission Hugh?

 

[lidirtrider]

Any word on if it'll work? I got a couple of 75's, that will be rephased by you Hugh, and I would love to do the swap.

 

[kopcicle]

http://i1100.photobucket.com/albums/g411/xscafe/service%20news/77%20xs/M7-023.jpg

~kop

 

[XSLeo]

Kopcicle, that's the info I remember reading. Thanks. Saved it so Ican find it next time I need it.
Leo