"A" and "AA" engines

Posted by Glenn Davis on April 02, 1997 at 18:08:28

I know that the "AA" prefix was for a heavy-duty clutch for trucks.
In 1928, all transmissions were heavy-duty and designated with an "A".
Only heavy-duty trucks from that point on were "AA". I have a 1931 "AA"
and I'm wondering is there any difference in engines? If not, why did they
have the "AA" designation?