Help me understand transmissions (especially AT545) and desirable model years

[cadillackid]

romani - go to the short bus forum and read 'the redbyrd transformation' that has all the answers to going to a 1000 from a 545..

yes the 1000 has overdrive.. double overdrive (its a 6 speed) + lockup

as turf mentions no transmission swap going from an at545 to another is 'easy' direct bolt up..

I was a hot-rodder for years.. so ive put all kinds of transmissions behind many different engines.. I was strictly GM so it was easy.. engines were either BOP or SBC. basically chevy or everything else.. transmissions were often made the same way in both flavors.. so I put 4L60E's behind Cadillac 425, a 200-4R behind a massive small block chevy stroker..

in the bus world you have SAE2 and SAE3 engines and transmissions.. sounds simple as there is only 2 right?

wrong

the AT545 transmission was an SAE3 ONLY.. the MT-643 was an SAE2 only transmission.. no other variations were made.. the bells were not swappable..

Unlike the car world where your transmission bell bolts directly to the engine Block, the engines have a flywheel housing that is bolted to the block.. that housing will terminate in an SAE2 or SAE3 bolt pattern.. (usually SAE2) an adapter ring was made to go from an SAE2 to an SAE3.. on the engine side..

lets take a common school bus engine, the navistar T-444E, that engine with an AT545 transmission... the engine flywheel housing was an SAE2.. then they put an adapter on to make it an SAE3. (to take the SAE3 AT545).. along with that they put a hub spacer on and a torque converter spacer ring.. thats specific for that transmission..

so lets say now you want to swap that AT545 for an MT643. sure you can take off the SAE3 adapter and now have an SAE2 engine mount.. great!

but wait. now your spacer hub for the torque converter pilot is too long... and oh the adapter ring is too deep... so perhaps navistar made a 643 mated to a T-444E. but you first need to figure out what in the heck the part numbers are for the correct spacer ring and hub adapter are... then actually find the parts... oh and a 643 weighs twice as much as a 545 so now you need some extra mounts.. many had cross-members.. (with an AT545 it just hangs from the bell..). so now you gotta find a cross member.. or you have the task of actually finding a junk-yarded bus with a T-444E and a MT643 to grab the donor adapter parts...

why I chose an allison 1000 -

the allison 1000 can be built with an SAE3 bell.. *AND* the offset of the torque converter and the bolt patter andhub size are IDENTICAL to the AT545.. and the weight is only 30-50 pounds heavier.. so now you just have to find parking brake lever brackets (if you have hydraulic brakes).. and shift brackets - though the geometry is the same.. so your AT545 RND321 lever will work still...

but wait theres more!

its an electronic transmission... it requires throttle inputs and tuning to operate just right and if you want it to work right with your cruise control you need to create a comms link between your engine and the transmission TCM.. and then your OEM VSS circuit will complain and cause issues with your dashboard speedometer and jack the ECM up with RPM de-rating if it cant read vehicle speed correctly for more than 2 minutes..

the moral of the story? buy the bus you want with the drivetrain you want..
emission-wise things started to get real in 2004.. the navistar VT-365 with its EGR issues (no it doesnt have the head issues the ford 6.0 did).. the MBE's that like to put more opil on the ground than circulate due to high crankcase pressures... nonetheless i just ran across a VT-365 with 400,000 miles on it not too long ago..

2007 / 2008 things got REAL with emissions - thats when DPF / DEF came into play. and those systems will SHut-you-down along the road if they malfunction too far.. or burn a hole in a piston... those early ones were not too nifty..

even the later ones are problematic though most of them wont ruin your engine now.. they will just shut you down..

my story of emissions - last year before i bought my DEV bus (ALL MECHANICAL DT360/AT545).. I had seen a pretty little white bus sitting out at the navistar dealer so I stopped to ask about it.. the sales guy heard me tell my story of wanting a bus just to cruise the country in and run a mobile DEV lab out of it..
" I have just the bus for you" - it was a brand new 2015 IC BE (had sat on the lot for over a year).. he said I can lease this to you cheaper than your silverado Pickup.. so we jumped the batteries.. drove it around to the front where the guy checked all the tires.. and off we went.. I drove it around the block,we pulled into a fuel station.. added a few gallons.. and it said something about REGEN on the dash.. it wouldnt go in drive.. I shut it off and back on and it just said 'regen'... and after a few more minutes it turned on a check engine light - flashing fast..the bus shut off and wouldnt restart.. that was it - we were done!. the tow rig came and took us all back.. I went on my way and never looked back..

-Christopher

 

[cowlitzcoach]

The best advice I would have for you is don't even look at a bus with an AT540 series transmission. It is a low HP, low torque transmission that was not designed for really big loads or high speeds. Since even the largest school buses fully loaded rarely weigh more than 26K, spend 90+% of their service life at speeds of under 35 MPH the vast majority of schools purchased the AT540 transmissions and had really good luck with them.

Schools that have a lot of hills would purchase hill route buses with higher HP and torque ratings which necessitated moving up to a stouter transmission which was the MT640 transmissions. The same happened if they ordered a bus that would be used on trips. Some even opted for the HT740 transmission if they got an engine with 300+ HP.

If you purchase a bus with the HP and transmission that will fit your needs the best it will end up costing you much less $$$ than if you end up having to change stuff. Swapping out rear gears can cost $1500 or more.

A Type 'D' rear engine bus with a big HP engine, highway gears, and pass through under the floor luggage compartments will have an initial expense much higher than a Type 'C' bus with a low HP engine, city gears, and no luggage compartments. But when you start to factor in the cost of upping the HP, upgrading the transmission, swapping rear gears, and building under floor compartments the higher initial cost becomes a moot point.

Also, almost every Type 'D' rear engine bus that was ordered as a trip bus will almost every time have the 12" windows. Almost every other bus built before about 2000 had the 9" windows which translates to 3" less inside ceiling height. There are some buses that have only 70" of inside ceiling height.

As far as emissions equipment are concerned, diesel rigs of the '00's and early '10's have had a lot of problems making the emissions work correctly. Some schools are actually hanging onto their older pre-emissions buses, if they can, for spare buses. The lack of electronics and emissions allow them to set on the back row for weeks or months and still start. Electronic buses with emissions will tend to go dead after several weeks, especially if the batteries are more than a couple of years old.

Which brings up another issue. Starting with the Thomas C2 Saf-T-Liner Type 'C' bus all buses have become multiplexed. Blue Bird and IC have done running changes to multiplexing and now all buses are multiplexed. It is a great idea and saves a lot of $$$ on building a bus but can become a total nightmare for a convertor. Adding circuits or eliminating circuits can render the bus a dead duck that isn't going to go anywhere.

I am sure some of those who post on this forum on a regular basis could figure out how to work around the multiplexing but it isn't something the average guy can do.

IHMO the best power package would be a mechanical Cummins 6CT or IHC DT466/530 with the MD3060 power package. You would have the advantage of mechanically operated engines with an OD transmission.

Good luck and happy trails to you!

 

[Rusty-SKO]

Thanks for schooling us skoolies: cadillac and cowlitz.:bow::bow: I sure enjoy sucking-up your knowledge. Thanks for sharing.

Sure would be nice if we had stickies on this Board.

:Thanx:

 

[EastCoastCB]

Okay, then what would you say is a good price premium to pay for a better transmission? Say that I could get a bus with an AT545 for $3,000 and we will assume that that's a "good deal" given the condition and characteristics of the bus. The exact same bus with an MT643 or some other "better" overdrive lockup transmission - what would you pay for that?

I only paid 2k and got air ride, dt466, and allison 643.
So if bus A has a 545 I just wouldn't buy it, and would go find one with the hardware I want.

 

[turf]

when dealing with these big mods.....truer words were never spoken.

cost becomes a moot point.

 

[BrandinoBeatz]

So you would 100% get a Allison 1000 over the mt643 trans?

as you might know I am looking to swap my at545 that's in my 1994 international vista(full size) that has a DT408 engine (has air brakes) with something better as I want to travel the country in it! I know it won't be easy but I do have a friend of mine that goes by @rosevillemarina on here who is willing to help me with the swap, he swapped whatever trans he had (maybe at545) in his vista short bus that has a t444e with a Allison 2000 I believe after people told him he couldn't!!! witch is admirable!

so just trying to know what the easier route and best transmission to swap my at545 with since I want to go through mountains and longer trips!

-thank you (Brandon)

 

[Booyah45828]

So you would 100% get a Allison 1000 over the mt643 trans?

as you might know I am looking to swap my at545 that's in my 1994 international vista(full size) that has a DT408 engine (has air brakes) with something better as I want to travel the country in it! I know it won't be easy but I do have a friend of mine that goes by @rosevillemarina on here who is willing to help me with the swap, he swapped whatever trans he had (maybe at545) in his vista short bus that has a t444e with a Allison 2000 I believe after people told him he couldn't!!! witch is admirable!

so just trying to know what the easier route and best transmission to swap my at545 with since I want to go through mountains and longer trips!

-thank you (Brandon)

Rolesville took the "easy" way out and bought a 2nd bus with the parts he needed. Easy is in quotes, as it's still a lot of work and modification to do such a swap, but he had most of the parts he needed from the 2nd bus.

To do this swap without a 2nd bus you'll have to be extremely mechanically inclined, as you yourself are going to need to know what parts are required, how they function, and where you get them. We can help, but we can't do it for you.

Rolesville was fortunate that his engine(t444e) could have been equipped with an allison 2000 in the later years of the model. I think the dt408 was phased out before the allison 2000's were phased in, so you'll have to get custom/creative when installing an allison 2000. The dt408 could have had an md3060, but it's not likely as that would have been a higher option and districts rarely chose higher options on the cheaper buses.

I don't know if people told rolesville that it wasn't possible. Some questioned about the why, as the vista isn't really a desirable bus. The vista is kind of a red-headed step child in that it's half a conventional and half an FE transit, but it doesn't get any of the benefits that are present being one or the other.

 

[Booyah45828]

Oh, and an allison 1000 is weaker then an mt643, but it has an overdrive, which is valuable in itself. The 1000 afaik was only used in gm pickups. What you're after is actually a 2000 series allison, as that was what was used in the medium duty trucks/buses.

The 1k and 2k are very similar, and you can build a 1k to be a-lot stronger then what it came with from the factory. Cadillackid did just that when he installed a 1k in his redbyrd bus.

 

[cadillackid]

Oh, and an allison 1000 is weaker then an mt643, but it has an overdrive, which is valuable in itself. The 1000 afaik was only used in gm pickups. What you're after is actually a 2000 series allison, as that was what was used in the medium duty trucks/buses.

The 1k and 2k are very similar, and you can build a 1k to be a-lot stronger then what it came with from the factory. Cadillackid did just that when he installed a 1k in his redbyrd bus.

*THIS* you dont want to buy a 1000 that was designed for a GM pickup.. even the pickup truck guys could burn up the C4 clutches with mildly tuned duramax engines.. so to use the 1000 i had mine built.. most places that build 1000s can build you one.. I wqent with a custom built 1000 as i knew in the future I may want to tune my engine and that I wanted a brand new trans vs a used one (that future is now.. my motor is tuned, my trans is tuned and I have had 0 issues since I did the swap summer 2017) a much cheaper route than I went is to do what rolesville did.. however like Booyah says you will need to do a much different throttle setup as the DT408 engine isnt electronic and the allison 1000/2000 are.. there are throttle boxes made which will mount to a mechanical linkage engine like your DT408 and produce an electronic signal for the allison 2000..



an MT643 is a very solid and beefy transmission (and hevy).. swapping one into a DT408 is pretty straightforward with still-available parts.. its a much heavier and better trans than a 545 however if your desire is to gain road speed it wont help, it is the same non-overdrive 1:1 configuration as your 545.. it has a lockup and much heavier clutches.. if you are fine wit hthe speeds you travel in your 545 than a 643 may be a good swap for you..



the biggest caveat to a 643 is if you have hydraulic brakes on your bus, the parking brake assembly for the 643 is getting tougher and more expensive to find... its a non issue if you have air brakes.



if you get serious about a 2000 swap and want options for a mechanical throttle box i can point you to a couple companies that make them. . installing one requires a bit of genoetry and possibly needing to fab up a bracket to anchor it.. its design is a cable that pulls out of a box, activating a sensor in the box.. so you attach it to your pedal or your pump linkage and go from there..

 

[Wuzabus]

Just to throw it out there.

Everything everyone has said about the 545 is correct. However.

I have the 542. It's the same as the 545 but with a smaller oil pan. It's not great, I'm not singing any praises, but ultimately it is adequate and works and I've put almost 25k miles on mine this year in every setting and every temperature across the US and I'm still rolling along fine.

Yes, more gears would be better. Lock up would be better. I'm generally rolling around 58mph because that's more or less the sweet spot of engine rpm vs making progress, another gear might add 10mpg or more to that.

The 545 is probably the most common transmission in these things in the 90s, and while it could be better, it could be a lot worse.

Your comment gives me CONFIDENCE to drive mine now. With all the negative press.. it made me want to STOP the conversion process and replace the transmission first before I go any further. However I did buy a trans cooler to install on Wuzabus. Hopefully that'll help my boy make it on a long trip.

 

[nikitis]

Your comment gives me CONFIDENCE to drive mine now. With all the negative press.. it made me want to STOP the conversion process and replace the transmission first before I go any further. However I did buy a trans cooler to install on Wuzabus. Hopefully that'll help my boy make it on a long trip.

Mines got the AT545 still too. It's reliable for me so far except when I pushed it past it's torque limites with an engine software horse power upgade. I had to downgrade it again, but then I took it on a 1500 mile trip and performed with zero issues, so it only seems to enjoy maybe up to 190HP, 210HP is too much for it.