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Old 05-12-2020, 03:49 PM   #1
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Unlocking 6th Gear for Allison 2500 Transmission, Is It Worth It?

Howdy!

After researching on this forum and the internet about the locked 6th gear in the Allison transmission, I'm curious as to why this is so important. I understand that it'll create a double overdrive and will drop the RPM's on the engine, but how much will this help a bus in true numbers? Has anyone done it and seen a substantial increase in MPG or lower RPM's? I'm not going to pretend I know much about buses, but I'm trying to learn and would appreciate real world information if it's available.

I ask because I have a 2007 IC with a 2500 Allison that can be unlocked. We intend to use our bus as a family vehicle and will be travelling from Waco, TX to Houston, TX every few months to take our boys to see specialists for their medical condition. Right now on short 30 mile trips I've taken to get used to driving the bus, I see that I'll probably be running at a top speed of 65 at around 2400 RPM, or most probably 62 at 2200ish RPM. The bus can get to 70, but it won't hold the speed when I set the cruise, but 65 or below is easy for it. I do know my bus has a 5.29 rear end. I'm not looking to get there fast, but anything I can do to squeeze out some fuel efficiency is what I'm hoping for.

After getting off the phone with the dealer who is currently working on some things for me, he said the cost would come to roughly $1K to $1200 by the time Navistar does their portion and Allison does theirs with the reprogramming. I've read about some of you paying a 3rd party $350 to unlock the gear, but using real dollars and cents, how quickly did you recoup the cost? And more importantly, has it truly been worth the investment; not in theory, but in tangible figures?
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Old 06-06-2020, 04:39 PM   #2
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No one has any real data from unlocking the 6th gear?
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Old 06-06-2020, 10:21 PM   #3
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Not sure if 6th gear will help alot but it should help out and it will lower the noise level inside the bus. And the issue with the bus not holding the speed at 70 on the cruise controll is more than likely in the computer they can set top speed and cruise speed in the ecm I bet your cruise speed is set to 65.
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Old 06-07-2020, 01:35 PM   #4
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Thanks DixonM for the reply. I have a new friend that just replaced the kingpins for us and noticed the top speed of 65 after a test drive to evaluate the repairs. He said he has the ability to reprogram the ECM and will delete the governor, so that should help with the speed as the bus seems to have no issues with power in the higher ranges.....on flat ground anyway.

Noise level reduction would be nice, but I'm not sure I can justify to my wife, or myself honestly, for spending up to $1200 and not seeing any real world benefit. I'm beginning to think the hype was more theoretical with the lack of responses, but I'll have no problem being proven wrong!
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Old 06-08-2020, 12:04 PM   #5
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Unlocking of the 6th gear can be done with the Allison DOC software. The newer buses 2003 and up are the easiest. It takes a few minutes. Depending on current installed software.
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Old 06-08-2020, 04:15 PM   #6
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Quote:
Originally Posted by AlexLasVegasBusSales View Post
Unlocking of the 6th gear can be done with the Allison DOC software. The newer buses 2003 and up are the easiest. It takes a few minutes. Depending on current installed software.
How is this exactly accomplished?
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Old 06-08-2020, 08:37 PM   #7
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DOC and an allison dealer level subscription.. just DOC on its own wont do it unless you have a Calibration file already ready to go.. ive done it by copying a cal from one TCM and programming it into another and it worked.. that was on a WTEC-III MD3060
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Old 06-09-2020, 05:31 PM   #8
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Originally Posted by cadillackid View Post
DOC and an allison dealer level subscription.. just DOC on its own wont do it unless you have a Calibration file already ready to go.. ive done it by copying a cal from one TCM and programming it into another and it worked.. that was on a WTEC-III MD3060
Is this something you still have the ability to do? I have read here that it's near impossible to get BB to allow Allison to unlock 6.
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Old 06-22-2020, 06:38 PM   #9
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Thank y'all for the responses. After finally speaking with someone in my area that has a great deal of knowledge with bus transmissions, we decided it's not worth it to unlock the 6th gear.

In our case and with my setup of having a 5.29 rearend, it's not due to any reason other than the 200 HP engine I have doesn't have enough juice to get me to a speed to use the 6th gear. I thought it was due to the governor, but after having the governor removed from Raising Wheels 1, he still only hits 65 MPH comfortably and to set the cruise. With the pedal on the floor he'll barely hit 70. So, even with 6th unlocked, the transmission would constantly be "searching", down and upshifting trying to find the sweet spot.

With our bus being used much differently than a typical skoolie, I was hoping to at least hit 70 on these long trips to Houston and to try and be less of a road hazard. But it is what it is and we were in need of the space, not speed. Besides, 65 with a cruise is pretty good from what I've read about some of these other buses!
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