AT545 performance questions

[ENGINE2]

Great site! I’m not doing a school bus conversion, however I’m in the market for a used medium duty truck and wanted to see if I could tap into the expertise here on this site. The vintage of trucks I’m looking at, GVWRs and drivetrains are very comparable to a school bus chassis. I find this site to have the most in depth coverage on these drivetrains, and the lighter/mid-duty Allison automatics that are common in school buses and medium duty trucks.

I’m looking for a Class 6 chassis, mid-1990s to mid-2000s. This was back when International dominated the medium duty segment, so I’m looking at 4700s, 4900s, and 4300s. I would also consider a Ford with a 5.9 Cummins with air brakes and possibly a GMC/Chevy with a gas or 3126 CAT. I’m definitely leaning toward International and there are more Internationals out there than most others, so I’m very likely to end up with one.

What I was hoping to get some feedback on though were the Allisons in these trucks. I initially was focused on getting a manual, but there are many trucks with autos out there. I’ve figured if the specs are good and the truck checks out, I should take the auto.

As those on this site would know, the AT545 is the most common auto in the trucks I’m looking at. I’ve come across some MT643s behind DT466s, but the T444E is far more common in the Class 6 Internationals. I also come across some Fords with 5.9 Cummins and an AT545. I’ve read many threads on the site regarding the issues and limitations of the AT545s, but I also read that they are relatively inexpensive to rebuild?, replace if needed.

I’m thinking that unlike some school bus conversions, my use might be ok for the AT545? I generally stay within 20-30 miles, much of that in typical suburban/rural driving on the roads the local school buses take. I do get up on an interstate which I use to go north/south at times. The 40-50 mile stretch I use is pretty flat. I guess this would similar to a local school bus on a field or sports team trip. I typically only run out to a location and back once or twice max a day and the truck will sit while I’m on-site.

GVWRs I’m looking at are 21,500 to 25,500 lbs for the Internationals. I might also be towing my 10k lbs equipment trailer. Realistically, my max GCW would probably be about 28k lbs, which would be occasionally. Typically I’ll be running in the low 20k lbs either GVW or GCW. I believe the AT545 is rated for up to 30k lbs, so I’m thinking I’d be ok? For those AT545 users, what do think about an AT545 behind say a T444E? or maybe a 5.9 Cummins? If either of these two drivetrains would be ok, that opens up a lot of trucks for me. Do you think I'd find the AT545 performance acceptable?

My other options are manuals, 5 spd or 6+1 in the Internationals, or a DT466 with either the older MT643 or have seen some newer 4900s with I believe a push-button MD3060? I read the MT643 would be good, but they seem to pretty rare in Class 6 trucks that I’m looking at. I haven’t read up much on the MD3060s. Also, not sure about the early/mid-2000s 4300s with DT466s, not sure what auto they use. The T444E backed by an AT545 is probably the most common International 4700 I run across - seemed like a very popular combo. I’m also somewhat interested in the Fords. I could get a mechanical 12V 5.9 Cummins with the AT545 instead of a HEUI T444E in the Internationals. Need air brakes with the Ford to stay away from the Lucas-Girling system.

Any comments on the AT545 or the other auto trans I’m running into, the MT643 or MD3060, would be appreciated given my intended application. Thanks in advance.

 

[magnakansas]

My opinion

545 is good for in town stop and go 0mph to 45mph.

643/653 good for highway - the converter can lock up, fairly stout unit.

3060 Same as 643/653 but a bit stronger and better suited to highway


William

 

[cadillackid]

545 is good for in town stop and go 0mph to 45mph.

643/653 good for highway - the converter can lock up, fairly stout unit.

3060 Same as 643/653 but a bit stronger and better suited to highway



William

3060 also has Overdrive.. double overdrive is typically enabled from the factory on the trucks.


2000 series is a good unit.. they started showing up in 2001 or so..





as for the 545... like magna says.. great in town and srtop N go... it will run on the highway but not under heavy loads.. you didnt mention what kind of loads you will be hauling... if you are running close to a rated GVWR of 26k or so the AT545 will struggle a bit on the highway... also you cant do any horsepower adders to the engines with the 545.. its a sure way to break the transmission..



you can add a large transmission cooler which definitely will help extend the transmission life.. heat os what kills the 545.. as does low line pressure at low RPM...



finding trucks that will travel 70 MPH and maintain RPM's of 2200-2400 will put more strain on the transmission, and generate more heat than trucks that are geared lower and have much lower cruising speeds..



dont fear the electronic engines.. the only ones at this point I would stay away from electronics wise would be the '3 box' systems which are getting difficult to get parts for.. they would be the T444E from 94 - early 97 and the DT466E from late 94 - 97.



an 'E' engine that has a large computer hanging off the side of the valve cover is a 'single box' and these still have readily available parts and the computers can be programmed for your VIN easily by an IH dealer..



when you hit 2004, the last year of the T444E (good non emissions).. but the first year of EGR on the DT466E.. EGR and its associated coolers were the begin of the decline of the DT466...



transmissions - Allison started selling the 'world series' in about 1995.. this is essentially a 3000 series... you can find them.. ive seen them..



the allison 2000 was released in the late model year 2000... its a 5 speed single overdrive unit and with lockup...





and of course there are various sticks out there.. the spicer 5 speed non overdrive is the most common in the 4700's but there were all kinds offered..

 

[nikitis]

dont fear the electronic engines.. the only ones at this point I would stay away from electronics wise would be the '3 box' systems which are getting difficult to get parts for.. they would be the T444E from 94 - early 97 and the DT466E from late 94 - 97.

CK knows I bought the 3 Box. I had a bad VPM on mine and I almost didn't find a working replacement. I have a AT545, and have had the computer unlocked (Not HP upgraded yet), but all restrictions removed when the new VPM was installed, and I have a T444E with AT545, and it could pull a house torque wise, but top speed is abysmal.

Fully unrestricted as I have mine, I'm now limited only by gearing. Most T444E's as I understand it are RPM locked in the computer to 2600-2700 RPM, while mine can redline and explode if I wanted to push it to do so well past 3600 RPM. (Not recommended to drive it past 2600-2700 RPM) But at 2600 RPM I can hit 60 MPH with a 4.78 Rear Axle Ratio, and 55 Mph at 2300 RPM, which is still kind of annoying but at least I can drive on one lane back roads without a line of cars piling up behind me now which I could not do before we removed all the computer restrictions completely. I was limited to 45Mph with the restrictions. They removed the speed restriction and the RPM restriction on mine.

Overall, with the Engine limited to safe values, the AT545 is stout, not good if you are wanting any kind of top speed at all. Just to give you an idea, you also need to ensure your brakes are in top notch shape because it has so much torque that if you are stopped and then let off the brakes, the bus nearly jumps up in the air upon taking off again, and if your brakes aren't working well you won't stop if you need to immediately stop like to avoid a kid running in the road or something. I had to redo my whole front end, but once the brakes were replaced it stops well now.

There are plenty of parts left for this bus still, but the only parts difficult to get are the 3box computer parts (especially VPM's, 1 of the 3 computers), and the air brake slack adjusters. I found OEM New old stock air brake chambers still for this bus, and purchased those and am using them so it stops good now. My bus is a 1995 IH 3800, though I found it was actually manufactured in September 1994, it's labeled as a 1995 on the title.

The 3 Box Thomas has the best body, Looks wise, and design wise in the way of longevity. Nothing rusts on it. It was hardly rusted at all spending all 30 years in Wet West Virginia, but they aren't worth it if they aren't mechanically functioning any longer. I may have to repower it with a modified modern engine setup in the future so I'm already factoring in the cost of that down the road.

 

[ENGINE2]

Thanks for all of the comments - great info. Sounds like I should stay away from the 3 box system. I see the difference looking at the engines, I want the single box that you can see hanging off the engine.

What about the 2004-2006 DT466E with the upgrades and egr? I know that this was probably the beginning of the end for the DT446, but should I walk away from the 2004 versions? Is this engine that problematic with egr, etc?

For transmissions, it looks like I should pass on the AT545. I do get up on the highway some and could do that at 26-28k lbs GCW. And we don't have any serious grades here, but I'd like to have some engine braking and ok performance on those grades. It looks as though most others trannys would be ok - MT, MD3060 and newer Allisons or a manual.

Here is a preference question I wanted to ask - buying used and with a budget, can't always find exactly what you are looking for. What I would like to get would be a DT466(E), manual, and air brakes. Air brakes are not that common in Class 6 trucks, would you take a T444E instead of the DT466E to get air brakes? And would you take an auto (not an AT545) trans instead of a manual to get air brakes. I read the hydraulic disc brakes are good, so not sure if I should give up on a DT466E or manual trans to get air brakes.

Thanks in advance for any additional comments.

 

[cadillackid]

whats your main use case?.. to me as someone who road trips alot in my vintage busses, I blew up 2 AT545's.. one in each of 2 busses.. driving back N forth to florida a lot from ohio.. (neither bus has a 545 at this point)..



the T444E is a great engine.. International made the engines for ford powerstrokes for many years.. the T444E is the Powerstroke 7.3.. in a bus they typically are SPec'd low horsepower and dont have a ton of torque (although they are easily tuned and cranked up.. as the 7.3 community is still very large)..



the later years 03/04 esp of the T444E were most often sold with a 5 speed Allison 2000 series transmission.. these will typically travel the highway nicely..


the DT466E was sold in everything from a lethargic low HP / low torque.. and with an AT545 often.. up to the rear engine busses that ran 275 HP with high torque and MD3060 tranmssions.. they can be tuned up.. starting in 04 they got EGR and a Variable Turbo... they had some issues but are still pretty solid engines.. in my opinion I prefer the late 97-03 (single box) versions.. although before the year 2000 there were a lot of 545's in school busses.. the MD3060 was around and the MT643 (Beefy, has a lockup but no OD)... once you reach 02/03 most of the 466E's ive seen were being sold with allison 2000 series transmissions.. you could still order an AT545 through mid 03 but most were not doing it anymore by then.



air / vs hydraulic brakes.. its more of a Spec thing than anything, im not sure at what GVWR that the hydraulics go up to.. but each district had their own ideas.. ive seen 5 window shorties with air brakes and 11 window conventionals with hydraulics..



air-ride suspension is something worth looking at too.. i have air ride on 2 of my busses and it makes a pretty good difference in how the bus drives .. air ride is a hit or miss as to whether ab us has it or not.. itas easy to tell from under carriage pics of the rear end if it has air springs or not.

 

[Omnibot2000]

For what it's worth.

My bus has a build date of October 2000. Has an Allison 2000 transmission.

Just to give an idea on availbility

 

[ENGINE2]

Thanks again for the info - now that I'm looking a little newer to avoid the Int'l 3-box system, I'm seeing more Allison 2000 series, which seem to have a good reputation from this site and others.

What about the older Int'l DT360s? Every once in a while I run across an older Int'l with the DT360. I read they are short on the power side. Mechanical so that's a benefit but can you source parts? I picked up a line set ticket for I think a 98 or 99 with a T444E and the guy at the parts counter commented "... that's an old one.." or something to that effect, so a DT360 will be even older . Any major parts issues with a DT360? I'm leaning newer single box to 2003, but I thought I asked about the DT360.

 

[Jolly Roger bus 223]

the 360 still has part and support available as well as horsepower upgrades.
my son just built up a school bus 360 to almost 400HP and we crammed itfer in a 2004 f350.
if you do decide to get one reach out to me and i can ask him where he sourced his parts.
i know carson stauffer diesel was a big help.
our biggest challenge was finding a machine that was reputable experienced and had the tooling to do the head upgrades.
good luck but with the older engines unless you can find a manual tranny then any automatic will likely be the 545 that is not very likeable if you are going to do alot of traveling and hill of any grade.

 

[cadillackid]

so I own a DT360 and a T444E..



if you want more pwoer the T444E is for you as far as easy power.. you call up PowerHungry and order an Orion for it and you have a ton of power .. the T444E is fundamentally the same as a ford powerstroke 7.3 (computers and accessory drives are different).. there is still huge afterkmarket parts and cooomunity support for it..



the DT360 out of the box is a bit short on power, however it is as rock solid as the mechanical DT466 of the same era.. they are all mechanical, simple, and are a wet sleeve engine so as logn as you dont overheat it badly or spin a bearing, it literally can last forever.. it can be "in-framed" (essentially rebuilt without pulling it out)...



I have a lot of respect for both of those engines.. there is a lot of community and parts support for it as well.. the DT community support is found on forums, dacebook, groups etc where people love to turn up the DT's and replace them into either their old classic rest-mod trucks or to replace crappy engines like ford 6.0/6.4


the simplicity of the DT means if electronics are not your thing but mechanics are more in your wheelhouse this engine is for you..



the AT545 is a transmission I would stay away from unless your bus is a classic that you are just going to driver now and then..


for a few years i was driging from ohio to florida and back easily 15 times a year.. and I blew up 2 AT545's.. one in my T444E and one in my DT360.. both busses now have different transmissions and I am much happier... the 545 is a great short trip transmission but run it on the highway with any kind of speed or an engine thats turned up and you'll probably eventually ruin it..


the allison 2000 transmission was introuduced in later year 2000 as a model year 01... it is a 5 speed single overdrive (0.74:1) with lockup converter...


the AT545 is a 4 speed non overdrive(1:1) with no lockup converter..


the DT360 never came with an Allison 2000 or an MD3060..


the DT360 was offered with the AT545 or the MT643 (non overdrive With lockup).. the MT643 is a heavy duty transmission and has lockup so it can run the highway like a champ ... and it can take pumpiing the power on your DT up to 250-275 HP without issue..

 

[cadillackid]

the 360 still has part and support available as well as horsepower upgrades.
my son just built up a school bus 360 to almost 400HP and we crammed itfer in a 2004 f350.
if you do decide to get one reach out to me and i can ask him where he sourced his parts.
i know carson stauffer diesel was a big help.
our biggest challenge was finding a machine that was reputable experienced and had the tooling to do the head upgrades.
good luck but with the older engines unless you can find a manual tranny then any automatic will likely be the 545 that is not very likeable if you are going to do alot of traveling and hill of any grade.

you are just the man I need to help me get a bit out of my A-pump on my DT360.. I need to understand how I can turn the screws a little.. my DTis awesome but it is a dog with both A/C compressors on trying to climb any kind of incline...

 

[Malevolence4845]

Question for the guru

the DT360 was offered with the AT545 or the MT643 (non overdrive With lockup).. the MT643 is a heavy duty transmission and has lockup so it can run the highway like a champ ... and it can take pumpiing the power on your DT up to 250-275 HP without issue..

not to highjack this guy's thread but you're easily top 3 people I see on here with a treasure trove of knowledge...would it be possible to replace my 545 with the 643? are they the same SAE bellhousing? I'd like the most from my DT360 and I've already planned on swapping my rear pinion out sometime later and looking at other tweaks internally.

 

[Jolly Roger bus 223]

you are just the man I need to help me get a bit out of my A-pump on my DT360.. I need to understand how I can turn the screws a little.. my DTis awesome but it is a dog with both A/C compressors on trying to climb any kind of incline...

.
when i talk to my son i will ask what he did. that was his project and i was his wrench monkey and general advice when he needed.

 

[cadillackid]

not to highjack this guy's thread but you're easily top 3 people I see on here with a treasure trove of knowledge...would it be possible to replace my 545 with the 643? are they the same SAE bellhousing? I'd like the most from my DT360 and I've already planned on swapping my rear pinion out sometime later and looking at other tweaks internally.

I did exactly that.. replace my 545 with a 643...



the *BIG* thing is if your 545 has a drum brake on the back.. the brake assembly will not move over to the 643.. you'll have to source one.. I have air brakes so i had no drum brake on the transmission.



the 545 is an SAE3 and the 643 is an SAE2.. the engine is an SAE2 with a ring that makes it an SAE3 so you remove that ring and now your bell will match..



you'll need to get a new flexplate ( the flywheel stays the same).. I think I have the part number someplace in my 'DEV RANDOM' thread. you remove the flywheel bolts.. old flexplate and the big spacer... you get shorter bolts (I used grade 8.. I cant remember the length.. you want a good bit of thread going into the crank hub.. I pulled my flywheel off and made sure my rear main seal wasnt leaking ..


reinstalled flywheel.. new flexplate, washer ring and new bolts... I Loctited the flywheel bolts and ran them in to 110 ft lbs.



now you can bolt your transmission up..



the cooler lines had to be adapted from #8 ORB to #12 ORB as the ports on the 643 are bigger..I got the partys at grainger.. #12 ORB going into the transmission down to a #8 hydraulic flare for the lines to screw on... the same lines work, the 643 makes less heat than the 545.. since id wasted my 545 I completely flushed my cooler loops and of course used new spin on filters.



make sure the 643 you buy has a tone ring and not a speedo gear.. if its from the 80s it may have a gear drive and not a tone ring.. 643 from the 90s made for a 2600-2700 RPM shift point would have a tone ring..


from the 545 you move over the Yoke, modulator, speed sensor, reverse light switch, neutral safety switch., shift lever linkage, dipstick.. (if your old 545 had a shallow pan and your 643 has a deep pan you'll need a new dipstick and tube or the levels will be measured wrong. I had to modify the shifter cable bracket a little down at the transmission..


I had my driveshaft shortened and balanced at a driveshaft shop.



my 643 was built for a DT466 so it shifts a little early on 3-4.. I could adjust it but havent.. when I need toi run out 3rd gear a bit I just pull the T-handle down into '3' and then back to D when i want 4th.. I rarely do it..