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Old 07-15-2014, 11:49 PM   #1
mtg
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Allison AT545 Torque Converter Swap

I have a 95 International 3600 with T444E and an Allison AT545, which doesn't have a lockup torque converter. Heat production going up hills in the mountains is really high, and its sucking fuel when cruising on the highway.

I have an aux trans cooler on the way to keep temperatures in check.

But, to reduce the heat production/power suck of the non lockup torque converter, I started looking into options. There isn't a lock up converter for that trans that I can find, but I can get a new torque converter from Suncoast that they claim will reduce engine speed at cruise by about 200-300 rpm via less slip.

I have some friends that are automotive engineers in Detroit, who mentioned that heat production is exponential with torque converter slip, so the torque converter swap ($600 plus labor) sounds like a pretty good way to go.

Has anybody done this before? Thoughts?
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Old 07-16-2014, 11:16 AM   #2
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Re: Allison AT545 Torque Converter Swap

I've never done it, but thought about it for a while. I was just going to get a converter from the factory because I read somewhere about 4 different stall options available (1 gas option, a v8 diesel option, and 2 inline six options). Then I started thinking about it and decided against it for the fact that a tighter converter would apply more power lower in the rpm range, which would cause the transmission clutches to slip more (supposedly this transmission is prone to that because the pump can't make enough line pressure).

Suncoast is correct in their claim of reducing engine slip with a tighter converter but I doubt you're going to see a 2-300 rpm differential out of it unless the input shaft rpm is below the stall speed of the converter to begin with.

I'm pretty against transmission swaps because of the amount of cost and labor involved to do it, but if you're looking to pull mountains in a bus and have reasonable highway cruising rpm, the at545 trans isn't the right trans for you. You'd need something with a lockup converter and Overdrive.
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Old 07-18-2014, 12:21 AM   #3
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Re: Allison AT545 Torque Converter Swap

For performance, a different transmission would be ideal, but I don't think its practical. On that note, though, has anybody swapped out an AT545? Is there something readily available for a reasonable price that is relatively easy to swap? If there's an easy enough swap, I'd consider that instead of swapping the converter.
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Old 07-18-2014, 12:35 AM   #4
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Re: Allison AT545 Torque Converter Swap

Swap in a manual transmission.
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Old 07-18-2014, 02:50 PM   #5
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Re: Allison AT545 Torque Converter Swap

Wouldn't it be easier to swap a different automatic, as it wouldn't require installing a clutch pedal and shifter?

I'm all for manuals (my daily driver has one), but that seems more difficult than switching to a different automatic. Maybe I'm wrong, though. I've never worked on a medium duty truck before getting this bus...
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Old 07-18-2014, 07:56 PM   #6
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Re: Allison AT545 Torque Converter Swap

Dunno. I was just thinking of how you could end up with a manual tranny out of the deal. You could buy another identical bus for next to nothing and swaparoo!
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Old 07-19-2014, 10:54 PM   #7
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Re: Allison AT545 Torque Converter Swap

Ha ha, fair enough. A 5 speed manual would be sweet.

Getting a donor bus to swap parts from could be a slick idea.
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Old 07-21-2014, 06:24 PM   #8
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Re: Allison AT545 Torque Converter Swap

Quote:
Originally Posted by mtg
For performance, a different transmission would be ideal, but I don't think its practical. On that note, though, has anybody swapped out an AT545? Is there something readily available for a reasonable price that is relatively easy to swap? If there's an easy enough swap, I'd consider that instead of swapping the converter.
No it's not practical. I've swapped out a few with reman units and it's pretty straightforward. All you really need is the right jack and handtools. The only reason I said it was because I really don't think a new converter is going to get you what you are after. A manual transmission would be kick-ass. I'd go with at least a six speed but an 8 would be easier to come by. But it would require quite a bit of fabrication to get the clutch to work right. Swapping it out of an identical bus would be the easiest but it'd be darn near impossible to find a bus made in the last 20 years with a manual transmission (at least around here). I hate to say it again but if you're looking to pull mountains in a bus and have reasonable highway cruising rpm, the at545 trans just isn't the right trans for you. No 4 speed can. You need more gear options and something with a lockup converter for the mountains and overdrive for the highway. There is just not really any other way around it
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