In my quest to find a good tranny to bolt up behind the DT360 that I eventually want to shoe horn into my truck, I've done quite a bit of research on the Allison tranny's and came up with a little info on them.
Many people have bad things to say about them, but I tend to think they would work quite well in a pickup if setup correctly. And seing how my truck / 5er combination is about the same size/weight of a 72 passenger school bus, the trans should survive just fine. This is all info off of the top of my head compiled from hours of internet searching, so I can't say it's 100% accurate; anyone feel free to correct me if I'm wrong.
The biggest downfall to the lot of them is no over drive.
4wd application would require a divorced transfer case.
There's 2 series of mechanical Allisons: the MT series and the AT series.
The AT's include the 540, 542, and 545. They have 4 forward gears.
540 and 542 were the earlier versions: basically the same as the 545 but with a smaller oil pan. The earlier versions all came with the same converter that was more for gasser applications, the later had 2 converters to choose from; 1 for gassers, 1 for diesels. The one for diesels is still really loose, and the lack of lockup on the converter means you pretty much run the engine to the governor and it just stays there. The fix to this is would be a tighter converter; Suncoast is the only place I have found that has any kind of aftermarket converter and cost is somewhere around $500. I've read several places that the shifts can easily be firmed up as Russ stated by adjustments in or behind the valve body; done by trial and error (and dropping the pan for every try), you can easily adjust the shift firmness right to the point that it spits the driveline out from under the truck.
I found one guy with a 12v Cummins pulling truck that ran a 545 and really liked it. He had some kind of aftermarket converter and a home made manual valve body. It was still good for highway travel with 38" tires. But the pulling organization ended up outlawing the tranny, so he changed to something else.
I've heard that the rare 1545 from military vehicles actually has a lockup converter but are hard as hell to find - Simp5782 has one.
I've seen them on CL for as little as $200, and as much as $1500 for one that was supposedly recently rebuilt. They are cheap and plentiful.
The MT series (like a 643) have some extra features over the AT series, but are bigger and a couple hundred pounds heavier. These guys do have a lock up torque converter. They have more torque capacity, some have a 5th forward gear. The extra gear is an extra box hanging off the ass end of the tranny that can only be shifted into manually - and they don't shift very smooth out of the low gear. In a pickup application, the low gear has a steep enough gear reduction it would be useless. The other cool feature is some can be found with a retarder bolted to the output of the tranny.
I've seen these on CL for $500 to $1500. Once again, somewhat cheap and plentiful.
Go to
this web page and you can download a whole bunch of info on them direct from Allison
