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Old 09-22-2020, 04:51 PM   #1
Join Date: Sep 2020
Location: Syracuse, NY
Posts: 19
Year: 2007
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Any thoughts on an Allison MT643 Transmission?

Looking at a 2001 Amtran International. 35". 173,000 miles. 7.3 Powerstroke Turbo Diesel Engine. Allison MT643 Transmission. We know to stay away from AT545 ... but we aren't so sure about the 643. Any thoughts or advice would be greatly appreciated!

Thank you,

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Old 09-22-2020, 04:57 PM   #2
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Join Date: May 2016
Location: Minnehaha Co., SD
Posts: 1,137
Year: 1996
Coachwork: Amtran
Chassis: International
Engine: DT466
Rated Cap: 65
Yeah, we're pretty happy with ours. I don't claim to know much about the nuances of Allison transmissions though. I guess its the big brother to the 545, but it's got a lockup torque converter so is better for highway travel, hills, etc. A little more robust than the 545 and doesn't heat up as much.
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Old 09-22-2020, 05:01 PM   #3
Join Date: Aug 2020
Location: Mesa, AZ
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Year: 2003
Coachwork: Blue Bird All American
Engine: 8.3 Cummins
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Also a 4speed auto rather than a 5/6? Curious if you like the gearing and acceleration. I would think that the 4 speed auto would have nice long legs to cruise on down the road.

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Old 09-22-2020, 05:54 PM   #4
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Join Date: May 2009
Location: Columbus Ohio
Posts: 13,930
Year: 1991
Coachwork: Carpenter
Chassis: International 3800
Engine: DTA360 / MT643
Rated Cap: 7 Row Handicap
the MT643 is an excellent transmission.. not only do you get a lockup converter , it is a beefier more heavy duty unit, so its more condusive to heavy loads, towing, and mountain travel..

it isnt any "faster" than an AT545 as like the 545 its a 4 speed with a 1:1 ratio on the top end.. non overdrive..

it shifts a tad rough for some people because it is heaby duty, doesnt bother me as i like that feel..

it definitelty doesnt make near the amount of heat that a 545 does..

ive gotten rid of 2 AT545s and one of them became a 643.. it works much better than the 545!!
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Old 09-22-2020, 08:26 PM   #5
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Join Date: May 2006
Location: mid Mo.
Posts: 379
Year: 1976
Coachwork: bluebird
Chassis: F33695
Engine: 427 chevy converted to 466
Rated Cap: 84
I just took a 643 out of my bus and it was 45 years old, 160,000 miles and working great, what better testiment to reliability than that. I changed it out because I went to newer driveline completely.
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