[Joe K]

You may have a broken gear.

The Ford four speed AA tranny has what is best described as a "creeper gear" in first gear. Not so much the 3 speed car/truck tranny - the same was used in both car or truck up until about October 1929 - which is why Ford allowed as option to buy a "Hi-Low" gear which effectively gave the AA trucks 6 forward speeds - at least one of these being equivalent to a creeper.

A 3 speed car tranny CAN be a bolt in - the four speed tranny was given as an option for those with automobiles desiring a power take off. No change in length. But the exchange takes more than just the substitution of the tranny: you need certainly the AA bellhousing and brake clutch parts that matches the tranny and a universal joint of specialized configuration to mate from the Borg Warner 4 speed to the Model A rear end.

I went through a similar exercise assembling the parts to go from a 4 speed Borg Warner Tranny to a Warford Overdrive (designed originally to mate against the 3 speed tranny.) And from the Warford to the Borg Warner rear differential/axle on my AA chassis (sniff - where did you end up and why did I sell you so cheap?) The specialized univeral joints have yoke half as is used on the Model A, with the matching yoke being made for the Borg Warner spline. For my AA I needed two of these. For your application you need only one.

These mix & match universals can be found in the flea markets - but might take some searching. Another source is Dana-Spicer who made universals for Ford "back in the day" and continue this tradition to today making an equivalent universal. And parts . Which are available to assemble the universal you need but there may be waiting period/special order issues.

Cracked and repaired several times has an ominous connotation. You could have the classic Borg Warner "smile crack" which is a sign of a compromised transmission (smile crack comes usually from the tranny being filled with water and freezing - but can be caused by abuse.) Smile crack can be seen as a semi-circular crack on the lower "belly" of the transmission: it can be repaired (I've seen it done by brazing) but can be a sign of misalignment between the internal parts of the transmission - and may cause the symptoms as you're seeing.

You might want to remove the top of the tranny and check out the positions of the "H" shifter pattern. Put the tranny in neutral and remove the top and (hopefully) find the two shifter sliders grooves opposite each other. (neutral, remember? This is where the right shifter HAS to line up with the left shifter to allow you to go between left and right in the lever action.) You may have one shifter out of sync which is causing the gears to clash. While you have the top off, take a look at the release lever shifter which you have to press down to allow the tranny to go into reverse gear (third shifter rail): this should be engaged as a lock preventing movement of the shifter lever to go to reverse.

Finding everything o.k. then you might want to start checking out the classified for a replacement 4 speed tranny. They can be had for fairly small money still, except for the ones that people have checked out and deemed AOK which sell for more. Even if you buy one from a basketcase AA, you likely can combine the parts of two trannies into one and make something that will work.

Hope this helps.

Joe K