AA 4 speed shift top

38 coupe

38 coupe

Well-known member
I have a neighbor with a 31 narrow bed pickup equipped with the heavy four transmission. The problem he is having is gear oil is leaking out past the shift rails in the top. I looked in the green book (I know, not the best source of information for Model As) and the line drawing of the top indicated there was a plug or seal or something that sealed off the ends of the shift rail bores. This makes no sense to me because the shift rails extend past the edge of the shift cover when you put the transmission into 1st and 3rd.

I am an early V8 guy, not a Model A guy. I have owned flathead V8s with the same four speed and don't remember them leaking from the top. What experience does everyone have with this? Is there a known solution to stop the gear oil oozing out?

Thanks.
 

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I just checked out an AA 4-speed that Ive set up to be used in an A chassis The shift rails do not extend past the shift cover when in 1st or 3rd.In fact,the rear bores are counterbored for the 3 welch plugs.The plugs are 3/4" and I think they are the same as the 4 used on the pan rails of most of the flat head V8s.Your neighbour must have shift rails that are too long,or perhaps a later shift tower?Most internal parts are the same from 29-52 except for the main shaft on open DS models.The reverse lock-out was used from 29-45.
 
I think that there are at least a couple of different shift tower configurations for the 4-speed transmission. I believe that the earlier tower did not have any provisions for plugging the bores for the shift rails and gear lube would leak. The later ones did have enough material cast in the tower so that plugs could be installed. I do know that I have seen tops that do have plugs installed.
 
Try lowering the fluid level. I fill mine up to the tip of my little finger. I'm not hauling anything but air and have kept the lever this low for years.
 
Thanks for the replies. My neighbor and I took an old rusty top with the capped ends from a 37 four speed transmission and rebuilt it. We found out the hard way that the shift rails have deeper detent slots in the later transmission. We put an AA reverse shift rail and the transmission wouldn't shift into 3rd or 4th. We swapped the shift rail out for the 37 shift rail and the transmission shifted properly.
 
Starting in feb 1930,the AA shift rail detents were made a bit deeper-by 1/32,"& the interlocks made longer.This info from page 420 of the A service bulletins.Ive had my reprint of the SB,s since 57 & find it indispensible.Your neighbour must have one of the very early trans which also explains the early shift hsg with open shift rails.
 
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