Determining the Right Allison Automatic. . .
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Cross-Country
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Determining the Right Allison Automatic. . .
I am hereby presenting this topic for those of you owners of medium-duty or medium-heavy crossover Ford trucks using Allison automatic transmissions.
How best to match the correct Allison automatic transmission to the various gas and diesel engines by torque converter size is what I am curious about.
The Ford F-series medium-duties could be had with one of two different varieties of Allison automatics: the AT540 series and the MT640 and MT650 series. The AT540 series had no lock-up clutch in its torque converters, but the MT600 (and HT700) series did. The MT650 series (except the MT654CR) had a super low 1st gear that was shifted manually (and thus only used for off-road purposes), while gears 2-5 worked the same as they do on the MT640 series. The MT654CR was a 5-speed close-ratio fully-automatic transmission with progressive shifting in all 5 gears.
The Louisville series had the same two Allison automatic series as options, plus the HT700 series for the 9000 series.
For example, say you have a 1983 Ford B-7000 diesel school bus capable of seating up to 66 students. It has a Cat 3208T diesel engine making 225 hp @ 2600 rpm and 585 lb/ft of torque @ 1400 rpm, coupled to an Allison MT643 automatic transmission.
Or say you have a 1983 Ford B-700 gas school bus, again capable for 66 students. This has a Ford 7.0L (429-4V) gas V8 engine making 200 hp @ 3800 rpm and 375 lb/ft of torque @ 2500 rpm, again coupled to the Allison MT643 automatic.
Three torque converters were made for the MT643 in 1983. The stall ratios were 3.09:1 (TC350), 2.43:1 (TC370) and 1.86:1 (TC380).
Correct me if I am wrong, but I believe the 3.09:1 stall ratio is the one to use for the gas engine (provided the speed where peak HP is achieved at is no higher than 4000 RPM), while the other two are for the diesels. The Cat 3208T, whose input torque rating exceeds the 1983 limits of the MT643's input torque capability, would need the 1.86:1 TC stall ratio.
~Ben
How best to match the correct Allison automatic transmission to the various gas and diesel engines by torque converter size is what I am curious about.
The Ford F-series medium-duties could be had with one of two different varieties of Allison automatics: the AT540 series and the MT640 and MT650 series. The AT540 series had no lock-up clutch in its torque converters, but the MT600 (and HT700) series did. The MT650 series (except the MT654CR) had a super low 1st gear that was shifted manually (and thus only used for off-road purposes), while gears 2-5 worked the same as they do on the MT640 series. The MT654CR was a 5-speed close-ratio fully-automatic transmission with progressive shifting in all 5 gears.
The Louisville series had the same two Allison automatic series as options, plus the HT700 series for the 9000 series.
For example, say you have a 1983 Ford B-7000 diesel school bus capable of seating up to 66 students. It has a Cat 3208T diesel engine making 225 hp @ 2600 rpm and 585 lb/ft of torque @ 1400 rpm, coupled to an Allison MT643 automatic transmission.
Or say you have a 1983 Ford B-700 gas school bus, again capable for 66 students. This has a Ford 7.0L (429-4V) gas V8 engine making 200 hp @ 3800 rpm and 375 lb/ft of torque @ 2500 rpm, again coupled to the Allison MT643 automatic.
Three torque converters were made for the MT643 in 1983. The stall ratios were 3.09:1 (TC350), 2.43:1 (TC370) and 1.86:1 (TC380).
Correct me if I am wrong, but I believe the 3.09:1 stall ratio is the one to use for the gas engine (provided the speed where peak HP is achieved at is no higher than 4000 RPM), while the other two are for the diesels. The Cat 3208T, whose input torque rating exceeds the 1983 limits of the MT643's input torque capability, would need the 1.86:1 TC stall ratio.
~Ben
Cross-Country
Joined: Jan 2017
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I'm sorry Ben didn't get more information back in the day because I'm sort of trying to work out a similar issue. I've got a 1991 F700 with the 6.6 New-Holland motor and the Allison AT is just killing me. I'm thinking changing to an MT643 or 653 would be a lot less work than doing the 5-speed thing but I need some help figuring out how to select the right torque converter and anything else in terms of the electronics involved in the swap.
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