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Old 09-19-2017, 12:10 AM   #1
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How to source a transmission upgrade

What is needed to source a transmission upgrade? My mechanic says he needs the serial for the transmission I want. I currently have 1998 5.9 12c w/ AT545. When I upgrade I want an MT643. I found this one on Craigslist. I've read the 545/643 is an easy swap - but what else do I need to know? https://baltimore.craigslist.org/pts...309146840.html


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Old 09-19-2017, 12:50 AM   #2
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Says out of pusher- Might be different.
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Old 09-19-2017, 05:34 PM   #3
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Says out of pusher- Might be different.


Excellent point. But still how do I properly source the right one? Serial?


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Old 09-19-2017, 06:19 PM   #4
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Pusher Should be the same transmission... the difference is in the rear axle. The engine and tranny turn the same way in my pusher at least.

The serial number is in the pictures on craigslist I would give your mechanic that number and the one from your transmission and see what he comes up with if your having him do the swap. I will tell you the housing is different on a 545 and 643 among other things

This is informative

https://www.google.com/amp/s/tatumsk...son-mt643/amp/
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Old 09-19-2017, 09:12 PM   #5
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With any mt643, there are a few things you need to consider. The main trans is the same, the valve body , torque converter, and governor are different between applications. Just installing the trans from some other rig can get you bad shift points, over or under revving and bad power and mileage. The best thing to do is get a trans from a rig like yours with the same engine and gearing.

As for swapping, you need a #2 flywheel housing (which you may allready have) flywheel and flexplate to fit. The cooler lines will be different. You will also need the driveshaft modified to fit or get one from the other bus.

I,m in the process of going from a manual to an mt643, It took a while to find a valve body for my application.
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Old 09-20-2017, 09:24 AM   #6
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With any mt643, there are a few things you need to consider. The main trans is the same, the valve body , torque converter, and governor are different between applications. Just installing the trans from some other rig can get you bad shift points, over or under revving and bad power and mileage. The best thing to do is get a trans from a rig like yours with the same engine and gearing.

As for swapping, you need a #2 flywheel housing (which you may allready have) flywheel and flexplate to fit. The cooler lines will be different. You will also need the driveshaft modified to fit or get one from the other bus.

I,m in the process of going from a manual to an mt643, It took a while to find a valve body for my application.
I had thought about changing our tranny too. I had no idea that there were so many considerations. I thought it was just a drop and swap kind of thing. I may just end up keeping mine.
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Old 09-20-2017, 01:56 PM   #7
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545 to 643 isn't too hard, and its a worthwhile upgrade if/when the 545 fails.
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Old 09-20-2017, 08:29 PM   #8
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I found just recently an attachment set up to add to my old 3-speed truck tranny to give it overdrive with nothing more than shortening the drive shaft.
And started wondering if they have one for the 545?
It was something like gearbox guys but i will have to find the sight again?
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Old 02-10-2018, 02:44 PM   #9
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So I found a used MT643 with only 41k miles not far from me -- for $500! Owner says it was pulled from a '98 bus and was connected to a 5.9 12v - just like my bus.

Let's say this is actually in good shape. What are some maintenance things I should do, regardless, before throwing it under my bus? I will have a mechanic do this, but I want a good understanding before I approach someone about it. Is there some measure of "refurbishing" that is always recommended?
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Old 02-10-2018, 04:34 PM   #10
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If it is in working order that is a deal. But make sure you get the shifter, all harnesses, any controllers and dipstick with it. They can add up top much more than the $500 in a heartbeat.
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Old 02-10-2018, 04:53 PM   #11
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If it is in working order that is a deal. But make sure you get the shifter, all harnesses, any controllers and dipstick with it. They can add up top much more than the $500 in a heartbeat.
Awesome thanks - I wouldn't have known to ask about those.

Turns out the seller is a diesel mechanic @ Cummins and is being quite helpful answering all of my questions. He says it's in great condition and worked perfectly when it was taken out of a mobile art museum that would drive around and visit schools.

What's the best way for a layman like myself to determine if I have an SAE2 or SAE3 bell housing?
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Old 02-10-2018, 04:56 PM   #12
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I believe all the Cummins 5.9's (as well as 4BT's) are all SAE 3 but you mechanic friend can tell you for sure.
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Old 02-10-2018, 04:58 PM   #13
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I believe all the Cummins 5.9's (as well as 4BT's) are all SAE 3 but you mechanic friend can tell you for sure.
Yeah he's saying it most likely is SAE 3, but sometimes they can be different. When it's done raining I'll try to figure out of there's an adapter or not.

Cool thanks for your help!
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Old 04-23-2018, 09:43 AM   #14
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This has turned into a much bigger ordeal than expected. :/ The MT643 in fact does not fit my flywheel so the shop has been trying to source parts and both Cummins and Allison have been giving them the runaround. Other issues are less problematic, but the MT643 has a mechanical speedometer and my AT545 has an electric one, so they need to convert it. Also something I never considered is that the MT643 requires beefier driveshaft ujoints than the 545. So they are recommending replacing the rear diff connector with a larger one, so that has to be dealt with as well.

Anyway - it's been weeks and little progress. The shop that has it is a charter bus company here in MD.
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Old 04-23-2018, 11:13 AM   #15
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talk to the folks at Custom Automatic Conversions (formerly cummins allison conversions).. and see if they can help wioth getting the corrdect part numbers for the adapters.

as for the driveshaft yolks and what not.. sure th3 643 might want them if you were running it behind a super powerful engine, but they arent required.. shortening the driveshaft is required and any shop can do that..

John bloem swapped a 545 for a 643 (yes on a navistar not a cummins) but the rear part didnt require alterations for the driveline / rear end.

speedometer, if the 643 you have has a cable only outpuit connection then you can get a cable to electronic converter device... dakota digital makes them.. it screws onto the cable output of a trans and converts it to electronic pulses.. some of them are programmable, you are shooting for 16 puklses per driveshaft rotation to match the 545..

you *MAY* be able to unscrew the cable speed sensor from the 643 and insert the 545 sensor and have it pick up the pulses as the gear goes bythe sensor.. the MT643 was also designed at 16 pulses per driveshaft rev..
-Christopher
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Old 04-23-2018, 11:15 AM   #16
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Originally Posted by cadillackid View Post
talk to the folks at Custom Automatic Conversions (formerly cummins allison conversions).. and see if they can help wioth getting the corrdect part numbers for the adapters.

as for the driveshaft yolks and what not.. sure th3 643 might want them if you were running it behind a super powerful engine, but they arent required.. shortening the driveshaft is required and any shop can do that..

John bloem swapped a 545 for a 643 (yes on a navistar not a cummins) but the rear part didnt require alterations for the driveline / rear end.

speedometer, if the 643 you have has a cable only outpuit connection then you can get a cable to electronic converter device... dakota digital makes them.. it screws onto the cable output of a trans and converts it to electronic pulses.. some of them are programmable, you are shooting for 16 puklses per driveshaft rotation to match the 545..

you *MAY* be able to unscrew the cable speed sensor from the 643 and insert the 545 sensor and have it pick up the pulses as the gear goes bythe sensor.. the MT643 was also designed at 16 pulses per driveshaft rev..
-Christopher
Listen to this guy, he's a GENIUS!!
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Old 04-23-2018, 11:50 AM   #17
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Originally Posted by cadillackid View Post
talk to the folks at Custom Automatic Conversions (formerly cummins allison conversions).. and see if they can help wioth getting the corrdect part numbers for the adapters.

as for the driveshaft yolks and what not.. sure th3 643 might want them if you were running it behind a super powerful engine, but they arent required.. shortening the driveshaft is required and any shop can do that..

John bloem swapped a 545 for a 643 (yes on a navistar not a cummins) but the rear part didnt require alterations for the driveline / rear end.

speedometer, if the 643 you have has a cable only outpuit connection then you can get a cable to electronic converter device... dakota digital makes them.. it screws onto the cable output of a trans and converts it to electronic pulses.. some of them are programmable, you are shooting for 16 puklses per driveshaft rotation to match the 545..

you *MAY* be able to unscrew the cable speed sensor from the 643 and insert the 545 sensor and have it pick up the pulses as the gear goes bythe sensor.. the MT643 was also designed at 16 pulses per driveshaft rev..
-Christopher
Thanks a ton! I will be passing this along to them!!
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Old 04-27-2018, 03:24 PM   #18
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Quote:
Originally Posted by cadillackid View Post
talk to the folks at Custom Automatic Conversions (formerly cummins allison conversions).. and see if they can help wioth getting the corrdect part numbers for the adapters.

as for the driveshaft yolks and what not.. sure th3 643 might want them if you were running it behind a super powerful engine, but they arent required.. shortening the driveshaft is required and any shop can do that..

John bloem swapped a 545 for a 643 (yes on a navistar not a cummins) but the rear part didnt require alterations for the driveline / rear end.

speedometer, if the 643 you have has a cable only outpuit connection then you can get a cable to electronic converter device... dakota digital makes them.. it screws onto the cable output of a trans and converts it to electronic pulses.. some of them are programmable, you are shooting for 16 puklses per driveshaft rotation to match the 545..

you *MAY* be able to unscrew the cable speed sensor from the 643 and insert the 545 sensor and have it pick up the pulses as the gear goes bythe sensor.. the MT643 was also designed at 16 pulses per driveshaft rev..
-Christopher
I talked with KC and she had fond things to say about you. She also said this is a tough conversion b/c she has no idea where to source an adapter plate -- and she may have convinced me to go the route of a 1000HS in the process of explaining the benefits of the better transmission. Awesome lady -- great advice -- now I'm freaking out about what makes the most sense. I can't seem to find a solid lead on an adapter plate for this, so maybe I need to scrap the 643 idea and get the better trans. Any thoughts?
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Old 04-27-2018, 10:29 PM   #19
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having swapped out a 545 myself (no more speedo), i don't think i'd go thru the hassle again for another 4 speed. i'd want at least 1 overdrive.

if i were to start over, instead of swapping transmissions, i'd invest in a 4.10 ring gear for the pumpkin.
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Old 04-27-2018, 10:53 PM   #20
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having swapped out a 545 myself (no more speedo), i don't think i'd go thru the hassle again for another 4 speed. i'd want at least 1 overdrive.

if i were to start over, instead of swapping transmissions, i'd invest in a 4.10 ring gear for the pumpkin.
My 98 shorty had a 444e and 545 with 4.10 rear.
the thing would do 70+ but the trans puts a TON of heat into the cooling system and it really would have been better off with lower gears or a trans with lockup tc.
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