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Old 10-26-2020, 10:41 PM   #1
Mini-Skoolie
 
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Does and MT643 have a TCM?

I was looking at a 1997 or 1998 International Conventional 3800 Bus with a DT466E and an MT643. Do these transmissions have a TCM?

What controls the shifting and convertor lockup?
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Old 10-26-2020, 10:45 PM   #2
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No, all mechanical.

The valve body above the trans fluid pan does the controlling of shifts and converter lockup.
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Old 10-26-2020, 10:52 PM   #3
Mini-Skoolie
 
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OK. That's sort of what I thought, but wanted to confirm.

From a longevity standpoint, are these pretty tough tranny's behind a DT466? The one I am looking at has 179,000 miles, but they say it cranks and hits the road fine. The fellow who owns it has a son in law that works for the school bus shop, and said this was a "good bus" -- they took the seats out and have used it for storage for the last 3 years, but crank it and drive it occasionally.

I know it does not have an overdrive, but I just want a trouble free automatic tranny. The bus is a 72 passenger.
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Old 10-27-2020, 12:26 AM   #4
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Nothing mechanical like an engine or transmission is every going to be "trouble free", especially with 179k miles on it. While the MT643 is better than the MT545 in general it is still a man made machine. When I check out a vehicle I always pull the engine and the transmission dip sticks and feel the oil between my fingers and smell the fluid to see if I detect any hint of burned fluid which would indicate overheating and lack of proper care/maintenance.
Unless they can produce documentation that the transmission has been rebuilt/replaced I'd assume it to have the full mileage on it and price it's worth accordingly. You'd also do yourself a favor and buy a BlueFire data adapter to read the true mileage and engine run hours on any bus you are looking to buy. Sometimes the dash data centers are replaced in school buses and the hour meter and odometer will be wrong so getting those readings direct form the engine control module (ECM) is the only way to know the true readings.
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Old 10-27-2020, 07:41 AM   #5
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automatic transmissions like mentioned are mechanical machines.. they also have wearable parts.. there are multiple sets of clutches inside of the transmissions.. how far worn or not is anyone;s best guess.. just Like brake pads on your car the clutches in an automatic wear based on use.. if the transmission is used in a highway application where ot goes into high gear and stays there for hours at a time, you can rack up a lot of miles and not much wear on the clutches.. of course anything spinning will have bearings and bushings.. if the transmission fluid was maintained well so the lubricity has been high then those bearings and bushings can last a lifetime.. on the other hand if said transmission was used in stop and go traffic where it constantly shifts then the clutches wear more.. putting more dirt in the fluid.. if that fluid is maintained well then the bearings will continue to last and be good..



on average talking to trans directors at schools they expect to rebuild the automatic trans in their busses at least once duringthe service life of the bus.. whether yours has been rebuilt or not is anyone's guess but if it has 179k of school bus route miles on it yet still works fine, I would still put it in your head that at some point you will need to rebuild it.



the good thing is that parts are still readily available for MT643 and its simple enough inside any qualified allison shop can put one together in a day..



like nentioned earlier in this thread.. if inspecting a bus in person, pull the stick.. if the fluid is brown or approaching black then that transmission is approaching end of life...



the MT643 as mentioned is all mechanical.. he is controlled by means of a modulator cable on mechanical engines.. the cable goes into the side of the trans and activates a valve .. that valve alters the valve body pressure from the governor .. the harder you press on the accelerator pedal, the higher the shift point and higher the shift pressure.. idea being that if you have it floored you want to "run-out" the gear as long as possible for acceleration and shift with high pressure so you dont slip the clutch.. when at light throttle, you want tto get into higher gears sooner for best fuel economy.. and shift at lower pressure so your shift feel is smoother.. shifting at high pressure under light-mid throttle is what us hot-rodders used to do to automatics to get them to screech the tires going from 1-2.. not something you really want to do to the driveline of your school bus.. so keeping that modulator in proper adjustment is paramount for transmission life..



if the rest of the bus is perfection for you yet the transmisison is a worry then you can always "fix it before it breaks".. last I knew LKQ in marshfield missouri still had some remanufacturered MT643's designed for DT466 engines for about $650.. a couple guys with the right tools can swap an MT643 in a weekend...
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Old 10-27-2020, 08:35 AM   #6
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Dt466E should have an electric modulator. So make sure it's functioning correctly and that's all you can do.

The mt643 isn't fool proof. It takes abuse better then the at545, but they do fail and wear out. The electronic allisons have nearly eliminated the transmission rebuild business. Even with the complexity of more electronics, they just seem to be so much more trouble free then the older mechanicals.
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Old 10-27-2020, 08:39 AM   #7
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Quote:
Originally Posted by Booyah45828 View Post
Dt466E should have an electric modulator. So make sure it's functioning correctly and that's all you can do.

The mt643 isn't fool proof. It takes abuse better then the at545, but they do fail and wear out. The electronic allisons have nearly eliminated the transmission rebuild business. Even with the complexity of more electronics, they just seem to be so much more trouble free then the older mechanicals.
The newer gen5 allison controls talk to the newer engines and actually reduce engine power during shifts which allows clutches to last triple or more what they used to, with less clutch material in the fluid the service intervals are longer and much less consequences for not servicing the fluid.
SEM or Shift Energy Management is what allison calls it. The TCM in my allison 1000 supports it and I messed with trying to support it on my t444e however the engine ECM is too slow to respond
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Old 10-27-2020, 10:12 AM   #8
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Thanks for the really good information. Especially about the SEM. We see this in the new cars and light duty trucks. However, we also see where they have used that as an excuse to make the internals less robust, and we are seeing transmission failures at lower mileages than we did with the old stuff.

6 speeds in Silverados and pickups failing around 100K or slightly over. $4400.00.
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Old 10-27-2020, 11:37 AM   #9
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well the allison 1000 / 2000 is 20 years old.. great transmission but its design isnt a match for the engines being built nowadays. . SEM shifts of not..



guys were breaking allison 1000's with 75 HP over-tunes back n the mid 00's.. now the engines are putting out well over 150+ more HP STOCK than they did back then .. SEM helps but essentially the limits of the 1000 are pushed with the current Duramaxx. its no wonder GM has decided to release a newer transmission.. they needed to..



I wouldnt even consider buying a stock 1000/2000 anymore except maybe for a school bus.. I went with a reputable aftermarket Builder and got a Built unit for my bus when I did the 545 -> 1000 swap.. while I have no plans to put a 500HP engine in front of mine, I wanted something designed to take the weight of a school bus and allow me to turn my engine up some and still retain longevity.
-Christopher
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Old 10-27-2020, 11:59 AM   #10
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Quote:
Originally Posted by cadillackid View Post
well the allison 1000 / 2000 is 20 years old.. great transmission but its design isnt a match for the engines being built nowadays. . SEM shifts of not..



guys were breaking allison 1000's with 75 HP over-tunes back n the mid 00's.. now the engines are putting out well over 150+ more HP STOCK than they did back then .. SEM helps but essentially the limits of the 1000 are pushed with the current Duramaxx. its no wonder GM has decided to release a newer transmission.. they needed to..



I wouldnt even consider buying a stock 1000/2000 anymore except maybe for a school bus.. I went with a reputable aftermarket Builder and got a Built unit for my bus when I did the 545 -> 1000 swap.. while I have no plans to put a 500HP engine in front of mine, I wanted something designed to take the weight of a school bus and allow me to turn my engine up some and still retain longevity.
-Christopher
What would you think about a 2000 Cummins 5.9 being mated to a 2000 in place of the ATA543? I'm wondering how difficult it would be to change the manual shifter for the electronic one on the 1000/2000.
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Old 11-03-2020, 05:29 PM   #11
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Quote:
Originally Posted by PorchDog View Post
I was looking at a 1997 or 1998 International Conventional 3800 Bus with a DT466E and an MT643. Do these transmissions have a TCM?

What controls the shifting and convertor lockup?
I admit to knowing nothing about the DTXXX engine world and the transmissions put behind them. But I can vouch for the MT64X series behind Detroit 6-71's and 6V92's as being as close to bullet proof as anyone would ever hope to find. My experience is that if the transmission shifts and locks up as it should, they usually run long enough to outlive the engines in service. That's assuming there isn't any problems like indicated in the check of fluid for burnt smell etc. If it's been serviced and not had dirt or other contamination get into the fluid I've seen these easily go for 4-500k+ miles with no trouble. Drive it till it breaks and then go buy a rebuilt one, they're actually pretty cheap and plentiful to find, and easy to swap in a new one. We don't give them much thought since they just keep on running. Extremely solid and well executed units. Mostly trouble free in my experience.
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Old 11-03-2020, 09:28 PM   #12
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That was very good info about the MT643. I realize that it has no overdrive, but I figured it was a simple durable tranny. I don't really know-- but suspected they got used in dump trucks and other medium duty vocational trucks years ago. They are probably cheap used because they are good.
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Old 11-04-2020, 07:05 AM   #13
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they were (are) cheap reman too.. LKQ in marshfield missouri was (still is) selling remans for $650..



the MT643 went out of new production in 2003. Navistar had a program they called 'ReNewed' in which you could get a reman transmission from navistar built to the original OEM spec of your truck.. they sold these through their dealer network for 15 years after EOL of new.. in 2018 they dumped their stock and obsolteted the part numbers in their computers.. LKQ bought them all.. (the same was done with AT545.. you could get those reman for $550).. they have been selling them out of their Marshfield missouri warehouse ever since..



these MT643s are 2600 RPM units meaning designed for the international Medium duty diesel engines as they pretty much all were designed for 2600 RPM maximum shift point of 2600 RPM..



if you were to use one on an engine with a 2400 or 2500 maximum RPM like some of the cummins and CAT engines you would have to either adjust the maximum modulator point diown a little or let off the gas a bit for it to shift up.. or you could change the governor to your original governor and perhaps adjust the pressure wheels in the valve body..



im running one of these transmissions in my DEV bus for a little less than 2 years and have zero issues with it.. for a DTA360 my 4th gear shift is a tad early but ive been too lazy to drop the pan and adjust the regulator valve up a couple clicks..



-Christopher
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Old 11-09-2020, 05:44 PM   #14
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Quote:
Originally Posted by Shamoke View Post
Nothing mechanical like an engine or transmission is ever going to be "trouble free", especially with 179k miles on it. While the MT643 is better than the MT545 in general it is still a man made machine. When I check out a vehicle I always pull the engine and the transmission dip sticks and feel the oil between my fingers and smell the fluid to see if I detect any hint of burned fluid which would indicate overheating and lack of proper care/maintenance.
Unless they can produce documentation that the transmission has been rebuilt/replaced I'd assume it to have the full mileage on it and price it's worth accordingly. You'd also do yourself a favor and buy a BlueFire data adapter to read the true mileage and engine run hours on any bus you are looking to buy. Sometimes the dash data centers are replaced in school buses and the hour meter and odometer will be wrong so getting those readings direct form the engine control module (ECM) is the only way to know the true readings.
Unless you have a 5.9 CUMMINS.12 VALVE MECHANICAL./darn caps
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Old 11-09-2020, 06:15 PM   #15
Mini-Skoolie
 
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12 valve mechanical Cummins.....Hmmmmmmmm....

If you fix the Killer Dowel Pin--

I have two 1996's and a 1998--- all with 12 valves in Dodge 3/4 ton pickups.

My DT466 Bus is mechanical too.

I'm ready for the apocalypse........
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