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Question for Tom C.  What are the differences in the MT 644 and the MT 647?
Thanks
J. PO

While you are waiting for Tom C., the 647 was an upgrade Allison did to the 644.  I don't remember what parts are different though.

On the older non World Allison transmissions, the first number was the series (size), second the number of speeds, and the third build type.  The 643 was just about the first in the series of 4 spd medium sized, with the 644 made with a larger torque converter to handle more horsepower.  The 647 I believe is a transit coach rated transmission with hardened input shaft and beefier clutches for stop and start.  There were so many builds on these transmissions, it's hard to keep track-especially since they are out of production with limited written resources left.  Good Luck, TomC

Thanks for the responses

Does any body have any specifications on the MT 644 and the MT 647.  I have looked on the internet for two days and have found nothing for the 647.  thanks

http://www.industrialautomatic.com/html/shuttle.htm (http://www.industrialautomatic.com/html/shuttle.htm)

http://www.allisontransmission.com/servlet/DownloadFile?Dir=publications/pubs&FileToGet=OM1334EN.pdf (http://www.allisontransmission.com/servlet/DownloadFile?Dir=publications/pubs&FileToGet=OM1334EN.pdf)

http://www.allisontransmission.com/servlet/DownloadFile?Dir=publications/pubs&FileToGet=OM1957EN.pdf (http://www.allisontransmission.com/servlet/DownloadFile?Dir=publications/pubs&FileToGet=OM1957EN.pdf)

http://www.allisonelectricdrive.net/publications/pubs/SM1546EN.jsp (http://www.allisonelectricdrive.net/publications/pubs/SM1546EN.jsp)

http://www.allisonelectricdrive.net/publications/pubs/PM2572EN.jsp (http://www.allisonelectricdrive.net/publications/pubs/PM2572EN.jsp)

http://www.transparts.ru/pdf/at640_04.pdf (http://www.transparts.ru/pdf/at640_04.pdf)