Allison AT545 Torque Converter Swap

[mtg]

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?

[Booyah45828]

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.

[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.

[opus]

Swap in a manual transmission.

[mtg]

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...

[opus]

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!

[mtg]

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

Getting a donor bus to swap parts from could be a slick idea.

[Booyah45828]

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

[hellicious_POP]

What about putting an mt 643 in? Still 4 speed from what I’ve gathered but supposed to lock up once in 3rd gear making it act like a 6 speed... I’ve read mixed reviews

[s2mikon]

How big of a cooler did you order? What is your stall speed now?

[s2mikon]

You probably didn’t buy that bus new so who knows what converter is in it now. I think that there were 4 options from Allison when new and god knows how many aftermarket units were rebuilt / hacked for it. It is very close to a turbo 400 6.2 diesel converter but not the same. I know that you can have custom converters made for it so I would call around. But knowing where you stall it now is a good place to start. If it stalls at 1500 rpm’s now I don’t think you are going to find anything to help you. If it stalls at 2300 rpm yes you can find some help. A tighter converter will also help coming down hills too.

[turf]

when i swapped transmissions, i swapped torque converters too.

i went from an at545 to an at1545 - the lockup uncle of the 545.

it also has the other torque converter offered with the diesel 545.

this one has a higher stall speed(?). at least i think that what it was. you rev higher before you launch down the road.

mine skips 2nd gear now, since the rpm coming out of first is 3rd gear territory.

i can;t say its better or worse than the original. its just different. the torque converter is no help with speed, it just launches different. maybe a bit faster.

don't swap an at1545. it was a military only application and there are no parts unless your mating it to a cat motor.

do swap in an allison 1000/2000. there is no benefit to swapping in another 4 speed.

[hellicious_POP]

Can I put a 1000/2000 on my mechanical 5.9 6bt? I’ve heard of people doing it but seems iffy

[Booyah45828]

Originally Posted by hellicious_POP

What about putting an mt 643 in? Still 4 speed from what I’ve gathered but supposed to lock up once in 3rd gear making it act like a 6 speed... I’ve read mixed reviews

Still a 4 speed. It doesn't act like a 6 speed, you just might feel 6 rpm changes depending on the torque converter locking/unlocking. It's better then the 545, but still a 1:1 ratio in 4th, so you won't gain any mph with the swap, which is what most are after.

[Booyah45828]

Originally Posted by hellicious_POP

Can I put a 1000/2000 on my mechanical 5.9 6bt? I’ve heard of people doing it but seems iffy

Yes, you can.

An electronic Allison can get by with only a throttle input, as all the speed sensors needed are located on the transmission. There is a thread on 4bt forums that you should read that will describe better as to what is needed. Or you can call one of the few allison swap shops and ask them to help, CAconversions is one that I know of that comes highly regarded.