Unlocking 6th Gear for Allison 2500 Transmission, Is It Worth It?

RaisingWheels1 · 05-12-2020, 03:49 PM

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?

RaisingWheels1 · 06-06-2020, 04:39 PM

No one has any real data from unlocking the 6th gear?

DixonM · 06-06-2020, 10:21 PM

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.

RaisingWheels1 · 06-07-2020, 01:35 PM

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!

AlexLasVegasBusSales · 06-08-2020, 12:04 PM

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.

Rovobay · 06-08-2020, 04:15 PM

Quote:

Originally Posted by AlexLasVegasBusSales

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?

cadillackid · 06-08-2020, 08:37 PM

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

JackE · 06-09-2020, 05:31 PM

Quote:

Originally Posted by cadillackid

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.

RaisingWheels1 · 06-22-2020, 06:38 PM

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!

RolesvilleMarina · 07-17-2021, 07:34 AM

you would be better off to replace or re-gear the rear end to a taller ratio

I have 4.73 and I run 64mph at 2k revs

cadillackid · 07-17-2021, 08:38 AM

Quote:

Originally Posted by RaisingWheels1

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!

what is your RPM at 65 or 70?

the T444E in my red bus runs awfully slow as im over-geared. i rarely use my 6th gear.. ive got the shift curve programmed to only use it at light throttle above 65 so it doesnt hunt.. now that I have the engine pumped up pretty good i can use it a little more.

sportyrick · 07-17-2021, 01:53 PM

Lowering the RPM's is better for everything, engine wear, fuel mileage, heat, noise, I don't think running 2400 RPM is the best for the engine, 2000 to 2200 would be ideal in my mind. My C7 turns 2700 at 70 MPH, not what I want for sure so I slowed down (my 7500 GMC service truck). My bus turns 1550 at 70 MPH with a 4.44 rear gear and 6 speed Allison but I am usually running in the 1600's and mid 70's MPH. I just sold 2 extra rearends to a company called Weller, they deal only in transmissions and rearends. When I was there I was talking to one gentleman and he said they try and stock a rearend for most anything so I am thinking I may call them back and see if they want the 45 year old Rockwell out of my bus that got changed out when I installed the DT466 (6:83 gears).

cadillackid · 07-17-2021, 02:16 PM

Quote:

Originally Posted by sportyrick

Lowering the RPM's is better for everything, engine wear, fuel mileage, noise, I don't think running 2400 RPM is the best for the engine, 2000 to 2200 would be ideal in my mind. My C7 turns 2700 at 70 MPH, not what I want for sure so I slowed down (my service truck).

every engine is different too..the V8 diesels like T444E and VT365 really like to cruise in that 1900-2100.. maybe 2200 RPM range..

the shorter stroke Inline 6's seem to like a similar range.

the Long stroke inline 6 like a Cummins 8.3, DT530 or DT466.. enjoy a 1700-1900 RPM cruise

with lower horsepower variants increasing the RPM slightly but still under the rated RPM can help with power..

Ideally an allison 6 speed properly geared is one of the best things ever.. the ratio change from 4 to 5 is steep its 1.0 down to 0.75(.74 on some).. but the 5 to 6 is incremental (0.75 to 0.65) so neing able to drop from 6 to 5 for just a little more power is a really nice thing... its also a shift which is easy to make in an allison. the things which need to happen to make a 6 to 5 then 5 to 6. C3 and C4 clutches see mt obe the most "easy-going" and all you do to go from 5 to 6 is trim the C3 amd C4.. its not a shift likely to bind or flare, easy to get pretty tight. if programmed correctly 6th gear should be designed to operate at fairly light load / throttle so shifting up and down quite a bit wont wear those clutches..

sportyrick · 07-17-2021, 09:21 PM

Thanks for the "second" on that cadillackid, I think it works out perfect especially since my engine us turned up a bit. Now since I have you on the horn how can I put a retarder in my 3060 and just use a switch to activate or do I need the "brains" telling it what to do? My brakes got so hot they quit working going down a 15% grade leaving Keystone SD. You think I can just pull the output end of tranny and do an install or is it a complete rebuild? It only has 30,000 miles on it.

cadillackid · 07-18-2021, 07:01 AM

Quote:

Originally Posted by sportyrick

Thanks for the "second" on that cadillackid, I think it works out perfect especially since my engine us turned up a bit. Now since I have you on the horn how can I put a retarder in my 3060 and just use a switch to activate or do I need the "brains" telling it what to do? My brakes got so hot they quit working going down a 15% grade leaving Keystone SD. You think I can just pull the output end of tranny and do an install or is it a complete rebuild? It only has 30,000 miles on it.

a retarder should go on copmpletely separate. allison does make 'R' suffix versions of many of their transmissions which included a retarder as part of the trans but I wouldnt mess with trying to convert your trans to an R, I would install a completely separate retarder like a Telma or similar which you can set up to actuate either with your brake light circuit or by a separate dash controller. if you manage to convert or replace your trans with an R version youll then need new programming in your TCM to support it

-Christopher

RolesvilleMarina · 07-18-2021, 02:37 PM

Quote:

Originally Posted by cadillackid

every engine is different too..the V8 diesels like T444E and VT365 really like to cruise in that 1900-2100.. maybe 2200 RPM range..

the ratio change from 4 to 5 is steep its 1.0 down to 0.75(.74 on some)....

I remember you teaching me this way back. I keep our T444E cruising right at about 2000-2050 rpm and get 64mph

I always thought I was .74 but now you mention .75 I wonder how to tell? Is it on the tag on the trans I wonder? Lucking out with a damn near new rebuild the tag is fresh and easily readable, but other than verifying A-2000 I never really looked at anything else then

She's been running great since I did the swap. We have been all over with it and 64mph (towing or not) seems to be her sweet spot

cadillackid · 07-18-2021, 03:34 PM

Quote:

Originally Posted by RolesvilleMarina

I remember you teaching me this way back. I keep our T444E cruising right at about 2000-2050 rpm and get 64mph

I always thought I was .74 but now you mention .75 I wonder how to tell? Is it on the tag on the trans I wonder? Lucking out with a damn near new rebuild the tag is fresh and easily readable, but other than verifying A-2000 I never really looked at anything else then

She's been running great since I did the swap. We have been all over with it and 64mph (towing or not) seems to be her sweet spot

they are a little different than each other.. some of the allisons have slightly different gearsets .. the 3060 is .75 and the general 2000 series is .74 .. the "international series" 2100/2200 typically in motorhomes is 0.71 like a 1000. for ive heard of some of the 2400 and 2500 PTS being 0.75 its a minuscule difference so really wont make much difference in speeds.. the trans serial number probably would let us find the exact number..

of course it all changed with the Latest greatest stiuff that came out a few years ago.. this is pretty much the single-reference data sheet for the modern stuff..

its really hard to keep up with

https://www.allisontransmission.com/....pdf?sfvrsn=13

RolesvilleMarina · 07-18-2021, 03:58 PM

Quote:

Originally Posted by cadillackid

they are a little different than each other.. some of the allisons have slightly different gearsets .. the 3060 is .75 and the general 2000 series is .74 .. the "international series" 2100/2200 typically in motorhomes is 0.71 like a 1000. for ive heard of some of the 2400 and 2500 PTS being 0.75 its a minuscule difference so really wont make much difference in speeds.. the trans serial number probably would let us find the exact number..

of course it all changed with the Latest greatest stiuff that came out a few years ago.. this is pretty much the single-reference data sheet for the modern stuff..

its really hard to keep up with

https://www.allisontransmission.com/....pdf?sfvrsn=13

Gotcha

so it is most likely our is a .74 I bet

sportyrick · 07-18-2021, 08:30 PM

The fifth gen Allison has got to be an electronic nightmare. Since we are off in Allison la la land how about this idea. There is no way I have room for an air conditioner compressor up front with the usual belt drive stuff on this DT466. How about this idea, this 3060 came with a full time PTO soe's how about I put my compressor back there? I think I have room and then I could have air conditioning running down the road? Yuk that means another space eater the condenser. By the way I looked into the telma and a used one goes for $2-3000 on ebay so I suspect a new one is $10,000. Jay Leno has a nice youtube about installing one on his fire truck, if he can afford it I know I can't.

cadillackid · 07-18-2021, 09:28 PM

The 466s will run dual AC compressors up front no issues. Or did you pretty much have to shoehorn it into your bus? I’ve never thought of running an AC on the PTO , I guess you need to make sure it can be active in all gears. Some Allison’s I’ve read can only run PTO in certain gears.

As for 5th Gen there’s no more wires than 4th Gen. it’s all done in the datalink .. id rather have a 4th Gen than a 3rd Gen anyway. More compact TCM, much better learning algorithms .. the single connector TCM, dual CAN ports so I can program the trans and monitor different data links without disturbing the J1939 comms.
5th Gen? Nada as allison is getting better at locking out everyone but dealers .

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