The Ford Barn

nosoup4u · 08-31-2018, 08:30 PM

What needs to be done to change a 3 to a 4?

1955cj5 · 08-31-2018, 09:25 PM

First of all, an AA four speed has nearly the same gear ratios in 2nd, 3rd and 4th (1:1 final) as the A three speed does in 1st , 2nd and 3rd (1:1 final).

What you gain with an AA four speed is a very low first gear...6.4:1 vs the A 3.12:1

The change requires a different, shorter clutch housing, to compensate for the longer AA 4 speed, and probably the toughest part to find is the special universal joint with 10 splines on the transmission end to 6 splines on the output/driveshaft end.

Info on the AA transmission change is here

http://www.fordgarage.com/pages/aafourspeedachassis.htm

And an earlier discussion here...

https://www.fordbarn.com/forum/showthread.php?t=167726

Now if you are talking a newer Ford 4-speed OD transmission, that is very different.....

There will be more responses!

nosoup4u · 08-31-2018, 09:35 PM

The granny low is what I'm after. See my other thread Car goes too fast!

1955cj5 · 08-31-2018, 09:42 PM

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Quote:

Originally Posted by nosoup4u

The granny low is what I'm after. See my other thread Car goes too fast!

The AA will give you that for sure....you can easily walk faster than the car will go idling in first!

Perfect parade gear....!

08-31-2018, 08:30 PM	#1
nosoup4u Senior Member Join Date: Dec 2010 Posts: 111	Are 3 and 4 speed trannies interchangeable? What needs to be done to change a 3 to a 4?

08-31-2018, 09:25 PM	#2
1955cj5 Senior Member Join Date: Apr 2015 Location: Boise, Idaho Posts: 1,578	Re: Are 3 and 4 speed trannies interchangeable? First of all, an AA four speed has nearly the same gear ratios in 2nd, 3rd and 4th (1:1 final) as the A three speed does in 1st , 2nd and 3rd (1:1 final). What you gain with an AA four speed is a very low first gear...6.4:1 vs the A 3.12:1 The change requires a different, shorter clutch housing, to compensate for the longer AA 4 speed, and probably the toughest part to find is the special universal joint with 10 splines on the transmission end to 6 splines on the output/driveshaft end. Info on the AA transmission change is here http://www.fordgarage.com/pages/aafourspeedachassis.htm And an earlier discussion here... https://www.fordbarn.com/forum/showthread.php?t=167726 Now if you are talking a newer Ford 4-speed OD transmission, that is very different..... There will be more responses! __________________ Early '29 CCPU that had a 4-speed, but not any more.......in the family since '62

08-31-2018, 09:35 PM	#3
nosoup4u Senior Member Join Date: Dec 2010 Posts: 111	Re: Are 3 and 4 speed trannies interchangeable? The granny low is what I'm after. See my other thread Car goes too fast!