34 & 39 gearboxes whats the differences

T

trevo

Senior Member
Ford Men, is there any great difference between these boxes and any advantage in installing a 39 into a 34 seems like its often done I assume the gearing is a little more comfortable for general driving??
 
Trevo, The '39 to '48 gearset is superior. Helical cut gears ('36 & later), provide a smoother shift, while the '39 & up synchro prevents grinding gears while shifting. Although all gearsets from '39 to '48 are basically the same, minor differences prevent individual gear interchange, so always match sets by year. You may have heard of using Lincoln gearsets, but these are not as streetable, being better for drag racing.

The 78 series ('37-'39) top shifter case is said to be stronger than earlier cases, but they are not bulletproof. If rebuilding any case, choose the '39 and up gearset, matched with the 91A shifting fork, required for those gears. This shifting fork is mountable on the earlier tower, as is the '39 tower mountable on earlier cases.
 
The gear shift lever to the top of the transmission is the sticking point. If you change to the 91A shift fork then the 34 shift lever will not be long enough to reach the forks properly. Changing to the later 39 style shift lever will reach the shift fork but will not have the necessary shape for the 34 above the transmission.
 
34 and earlier cases are not relieved enough to clear centrifical clutches used on later cars.
 
All good info but I'm quite sure the 91a 2nd/3rd fork will not work in the '32 - '35
slant back tower. This is a pretty important point to not loose track of.
Charlie ny
 
Thank you all for the info I am trying to get the car a little more drivable without compromising originality too much
 
I misstated earlier, and agree that the 91A fork will not work with the slant tower. The choice of gears is open to the 48 and 68 cases, but the later gear choice must include the 68 or 81A tower, to include the 91A fork needed with those gears.
 
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