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Old 05-11-2022, 03:52 PM   #1
Mini-Skoolie
 
Join Date: Oct 2018
Location: Illinois
Posts: 14
Year: 1999
Coachwork: Blue Bird
Engine: 24-Valve 5.9 Cummins
Rated Cap: 67
Transmission for Cummins 5.9 vs 6.7

Hi all -

I'm in heavy research mode as I'm looking to swap my 545 trans. I have a '99 24-valve Cummins 5.9 in a 30' Blue Bird. I want to get a more stout trans with lockup converter as a minimum, and would LOVE to get the RPMs under control with an OD option. I have a good lead on an MT643, but that would also come with a lot of conversion parts due to change in bellhousing size (I have an SAE3, and the MT is 2) and no OD. But I have a parts list and can pull the trigger on that idea.

HOWEVER - I can only do this once...and I'm not even sure I can afford the ONCE! ha ha. So before I do anything, I want to exhaust my search. A long train has lead me to what I think are my best 2 last options: the aforementioned 643, or possibly an Allison 2500 PTS (as suggested by a helpful Skoolie.net friend!).

Here is the question: I have a lead on a 2500 from a 6.7 Cummins. It is my understanding that the 5.9 and 6.7 are VERY similar, especially "externally." Is it a safe assumption that if a 2500 is coming from a 6.7, that it should bolt right up to a 5.9 (not just bell housing, but also flex plate, adapter, etc)? I'm under the assumption that when it comes to the TCM, I would have to buy that separately to match my application. I'm also assuming that a drive shaft shortening may also be on the table (also with the 643). But as far as the mechanics, should I assume they should match?

Thank you in advance for any clarifications on this!

Shane

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Old 05-11-2022, 04:12 PM   #2
Bus Crazy
 
Join Date: May 2018
Location: topeka kansas
Posts: 1,794
Year: 1954
Coachwork: wayne
Chassis: old f500- new 2005 f-450
Engine: cummins 12 valve
Rated Cap: 20? five rows of 4?
What I think I know

The stuff at the back of your 5.9 Ö. Bell housing, flexplate, adapterÖ.. leave it alone. Buy 2400 pts with #3 housing. Use the fellow that Cadillac has purchased from, get your TCM, throttle position sensor, and harness from him. If the transmission is older it might only be five speed, but 5th gear is around .73 overdrive. There is a sweet spot for the year of manufacture for the valve body stuff, really new has itís own complications.

There are 2400 series transmissions #2 housings.

Cadillac- you chime in here or some body direct this fella to the transmission swap on redbyrd

William
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Old 05-11-2022, 04:20 PM   #3
Bus Nut
 
fo4imtippin's Avatar
 
Join Date: Oct 2021
Location: Jacksonville, FL
Posts: 783
Year: 2003
Coachwork: BlueBird
Chassis: TC2000 28ft
Engine: Cummins ISB 5.9 24v, MD3060
Rated Cap: 14
This is a good video on the topic. He has a 24v Cummins with sae3 housing. He decided to drop a manual in..


https://youtu.be/V4Xh6ur246k
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Old 05-11-2022, 04:33 PM   #4
Mini-Skoolie
 
Join Date: Oct 2018
Location: Illinois
Posts: 14
Year: 1999
Coachwork: Blue Bird
Engine: 24-Valve 5.9 Cummins
Rated Cap: 67
wrong post! sorry
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Old 05-11-2022, 04:34 PM   #5
Mini-Skoolie
 
Join Date: Oct 2018
Location: Illinois
Posts: 14
Year: 1999
Coachwork: Blue Bird
Engine: 24-Valve 5.9 Cummins
Rated Cap: 67
Thank you, William. This is what I was hoping to hear. I spoke with an Allison guy and he rained on my parade and made it sound like I would have to buy all new guts. But he also didn't know the 6.7 existed, so I wasn't sold on his assessment...or I just did WANT to believe him...

Thanks for this information.

(CadillacKid has been giving me a lot of ideas already. Trying to give him a rest...ha ha. Thank you to both of you!!)
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Old 05-11-2022, 06:13 PM   #6
Mini-Skoolie
 
Join Date: Oct 2018
Location: Illinois
Posts: 14
Year: 1999
Coachwork: Blue Bird
Engine: 24-Valve 5.9 Cummins
Rated Cap: 67
Quote:
Originally Posted by fo4imtippin View Post
This is a good video on the topic. He has a 24v Cummins with sae3 housing. He decided to drop a manual in..


https://youtu.be/V4Xh6ur246k
Thanks for the link! Iíll check it out!
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