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Old 02-13-2007, 10:38 PM   #1
Join Date: Dec 2006
Location: Whidbey Island, Washington
Posts: 14
Year: 1980
Coachwork: Crown
Chassis: 3 axle (10 wheel)
Engine: GMC 6-71 T
Rated Cap: 97
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Allison shift point

have an Allison MT-644 behind a 6-71-T. The engine no load high
idle is about 2650 and the high idle under load is 2400. The
transmission shifts at 2100. This seems low on the power curve. I
would be interested in knowing other people's shift point and if it is low, is it
practical to raise the rpm where the shift occurs?

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Old 02-13-2007, 11:14 PM   #2
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Join Date: Nov 2003
Location: Twin Falls, Idaho
Posts: 809
The master of Allison auto trans

A good auto trans mechanic and shop owner in your area is....
Harry at Power Shift NW... Woodinville.. 425 487 1535
When ya call him, have all the data ready to tell Harry. He wants all the info on the trans tag. Harry has the books and lots of experience. Be ready with your engine type, number, type of bus, rear axle numbers. Harry will give ya lots of information and advice. I'm going to him shortly so he can change my trans shift points. Tell him, Frank, from Idaho gave ya this information.
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Old 02-14-2007, 06:00 PM   #3
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Location: Saint James, MN
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How do they change the shift points on the mechanical
Allisons? Is it just a modulator swap like on a Turbo 400?
Skooling state at a time...
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Old 02-14-2007, 08:17 PM   #4
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Location: Twin Falls, Idaho
Posts: 809
Allison trans shift points

Allison determins shift points by, throttle position, govenor, engine type and application. The major adjustments are done in the valve body, with the Allison book, many years past experiences, and application. A farm truck will not have the same shifts as a bus or a local delivery truck. The rear axle ratio also affects the adjustments. Harry is da man. Frank
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