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Old 01-15-2019, 08:54 PM   #1
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Advice on engine and transmission for short bus conversion

Hello!
This is my first bus conversion and I am looking to get a short bus that will be used for travelling across North America. Currently, I am feeling a bit overwhelmed with all of the engine and transmission options out there, and since I am not even remotely a mechanic or even know much about this stuff, I am in need of some help and direction!
I've been told by my uncle (who is a mechanic) that the Navistar international DT466 and Allison transmission (standard or automatic) are the way to go for longevity in a short bus conversion, but any feedback on that or other opinions, advice, or suggestions on other engine and transmission models would be much appreciated!

Thank you for your help!

Hunter S.
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Old 01-15-2019, 09:39 PM   #2
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Hello and welcome to the forums!

Your uncle was dead on right, the Navistar brand is one of the most recommended engines on here, specifically the DT466 and DT466e. The DT444 is better than a, say, Mercedes, but overall the DT466 seems to take the #1 place.

As for the transmission, Allison is most likely what you'll find in almost every bus you look at, but the model is important. Well, mainly to avoid one. Out of all of their wonderful transmissions, the least recommended is also the most common - the 545. It's manageable, I recently bought a bus with one in it, and despite expecting to plummet off a cliff on a hill, it actually drives decently as long as you are okay with the following things:
  • You're not going to go fast as you could with overdrive
  • You will go slower on inclines and lack engine braking on declines.
  • You're not looking to go faster than 55-60mph on level road

The other wonderful Allison transmissions are not unicorns, but they are uncommon. We're talking Scyther, not holographic Charizard. These are the AT643 and AT3060. These have both overdrive and locking torque converter, which will help greatly on hills and with top speed.

To clarify, the AT545 lacks both overdrive and locking TC in any gear. The toque converter will essentially be "slipping" the entire time, generating a lot of heat. For this reason, if you are planning long trips or hilly travels with a 545, you'll want an additional transmission cooler.
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Old 01-15-2019, 10:01 PM   #3
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As far as engines they're all about as good as each other up to 2004. Pick your flavor but Cummins, Cat, and Navistar and the "big three" in school bus engines.
Brand loyalty is wasted in this type of machine. Find a clean, rust free pre-emissions bus that's been taken care of and is setup close to what you need and run with it.
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Old 01-16-2019, 06:07 AM   #4
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in general terms, the inline 6 diesel engines (DT-466/CAT-3126/Cummins 5.9 / Cummins 8.3). will have more torque than the V-8 Diesels (T-444E(some call it a DT444), VT-365, CAT320.


ECCB has it right.. the general consensus is that reliability seems to go downhill on many of these enfgines in the 2004-2005 model year range and up.. and inthe 07/08. and newer range full-on emissions were required which further increased complexity and seemed to reduce reliabilty..



short busses - there are different types of shorties.. alot of drivetrain options depend on which type you are looking at..



there are the Cust-away shorties.. which the front part looks like a standard chevy or ford Van.. and the back looks like a school bus.. there are various drivetrains all of which you can generally buy parts at your local auto store for.. in the chevies the gasoline 6.0 litre is a favorite as its reliable and parts are everywhere.. you'll likely have a GMC 4L60E or 4L80E overdrive transmission.. Duramaxx and 6.5 litre were diesel options for these in the 00+ years.. if you get the duramaxx you'll have an allison 1000 transmission..



in the ford cutaways you'll most often find a Powerstroke.. stick to the pre 04 years and you'll get the venerable 7.3 which is generally a reliable diesel in these vans and is pre emissions.. the 6.0 diesel can be a reliable engine, however its not for thew faint of heart.. as in its early years for sure, it had serious issues well documented on the internet.. and requiring (Bullet-proofing) to make it good.. if you have no mechanical knowkedge tend to stay away from the ford 6.0 diesel..





now the other type of shorty bus is a CE or conventional.. which looks just like a big bus but is shorter.. International and freightliner are the 2 main chassis you'll see.. and the bodies were made by a myriad of manufacturers over the years.. these tyype busses will have truck drivelines in them. and are where you'll find your truck engines like the DT466 or CAT3126. and others.. thje allison transmision options were many depending on the type and year of the bus.. the allison 545 was the lowest cost option. and was a fantastic transmission for in-town bus route use, however on the highway esp in the mountains it can be lacking. due to it not having the locking torque converter... in a shorty bus they can be fun, esp if you keep the fluid fresh and install a high performance transmission cooler....



the T-444E is a very similar engine to the ford powerstroke 7.3. international built them for ford.. it works well in a shorty bus. but lacks in power if you buy it in a full length bus.. 2004 was its last year in conventional school busses..



be patient, read threads about real world results of various busses and thse on here.. people taking trips often post MPG results, accounts of how their bus does, etc.. those are the real world experiences you want to learn from before you go out and buy a bus..



-Christopher
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Old 01-16-2019, 08:32 AM   #5
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Chris in the cut away chevy and gmc's they didnt give them the allison 1000 they put the 4L85E in those due to the fact the power on the duramax was cut down for van use. I wish they had the 1000 in the cutaways
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Old 01-16-2019, 08:35 AM   #6
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I thought the duramaxx 3500 series vans had the 1000s with the straight cut gears.. or did they get the 6L90s in the vans with 6 speeds?



-Christopher
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Old 01-16-2019, 09:05 AM   #7
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the 6l90s didnt come out till i think 2009 or 2010 the 4l85e is pretty much the same as the 4l80e with the different gearing. not sure why they didnt use the 1000 maybe for cost or the fact they kept the power down to only 250hp
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Old 01-16-2019, 09:49 AM   #8
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the original Gen 1 1000s had strength issues.. just ask the duramaxx giuys trying to tune more than 50 additional horse in their pickups... they glaze the clutches and limp the computer..



the allisons did make it into the heavier trucks.. 4500,5500, etc..



and they are stronger now.. plus you can build them to be wicked strong.. the one I used in my bus is built for gobs of HP and torque.. which is good because im now into the crank up the power and torque phase on my engine.. .. not really because I need to go any harder or faster but building fast is in my blood i guess..

-Christopher
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Old 01-16-2019, 09:53 AM   #9
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Just a little clarification....

The MD3060 and the MT643 are both good transmissions for our application. However, the MT643 is NOT an overdrive.

Carry on....
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Old 01-17-2019, 10:20 AM   #10
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Thanks to everyone for the advice! This was super helpful and I appreciate everyone taking the time to point me in the right direction.

Cheers,
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