Allison MD3060 unlock tutorial

[Mgulley82]

Does anyone know what rear end ratio would render a 6th gear mostly useless?

Essentially: is there a max rear end ratio which becomes the limiting factor for top speed?

Currently my 04 Thomas 40’ FE peaks at around 65 mph in 5th gear on level, 67 down hill, 62 uphill

[PNW_Steve]

Originally Posted by Mgulley82

Does anyone know what rear end ratio would render a 6th gear mostly useless?

Essentially: is there a max rear end ratio which becomes the limiting factor for top speed?

Currently my 04 Thomas 40’ FE peaks at around 65 mph in 5th gear on level, 67 down hill, 62 uphill

It depends on your tire size, engine and desired top speed(or cruising speed).

My Bluebird has 11r22.5 and , 8.3 Cummins and 5.38 rear gears. It goes fast enough in 5th (67+) but is wound up tight. I want 6th to reduce rpm at highway speeds.

If my rear gear was much taller at all I probably would not be looking to unlock 6th.

Personal preference : I think that 65mph is plenty fast in a 26k lb bus. Fuel mileage in my bus drops notably when I run 65mph Vs. 55mph. If I recall, drag increases with the square of speed and overcoming drag is the primary consumer of hp/fuel at highway speeds.

[Twigg]

Originally Posted by PNW_Steve

It depends on your tire size, engine and desired top speed(or cruising speed).

My Bluebird has 11r22.5 and , 8.3 Cummins and 5.38 rear gears. It goes fast enough in 5th (67+) but is wound up tight. I want 6th to reduce rpm at highway speeds.

If my rear gear was much taller at all I probably would not be looking to unlock 6th.

Personal preference : I think that 65mph is plenty fast in a 26k lb bus. Fuel mileage in my bus drops notably when I run 65mph Vs. 55mph. If I recall, drag increases with the square of speed and overcoming drag is the primary consumer of hp/fuel at highway speeds.

You have the same drivetrain as me.

I have a request in with Thomas, but as yet I haven't heard of them agreeing to the unlock with an FD higher than around 6.14.

I'm hoping they will agree. 6th would give our buses a top speed of around 75-77 mph, but more importantly reduce the cruising rpm and aid fuel economy.

FWIW, the 8.3 in standard trim can handle 3400 rpm before the valve springs need changing. That would increase the speed available, but cost fuel.

[family wagon]

My local Allison shop quoted me about $300 for calibration changes when I asked several years ago. Sending $400 to PCM, plus the work of removing and shipping the physical box, does cost more... but then again it's not fair to compare the price of getting it done to the theoretical price of "if we could.. but we can't." They sound like a pretty good deal.

I wonder whether the shift points for the other 5 gears change -- I've considered finding a vocational truck with an MD3060 and using it as a carrier to take my tranny computer to Allison for re-programming. Or just buy the computer out of a wrecked truck. But I'm concerned about whether its programming will be a good match to the tune of my engine and the characteristics of my bus. Have PCM reverse engineered this thing, or do they use a hack like putting the computer into an approved vehicle and using the existing Allison procedure?

To the earlier question about rear end ratio: I have one bus with the ISC8.3 with a B300R transmission (fundamentally the same as MD3060, I'm told) and 5.38 rear end. I have the same view as PNW_Steve: it goes as fast as I want it to, but I'd like to not have the engine bumping its rev limiter (2450 RPM?) at the same time.

I also have a bus with the ISC8.3, MD3060, and a 4.78 rear end. I'm hoping that one will be running in the next week or two, and maybe I'll do a race with the two buses so I can see which axle ratio I like most. I'm expecting this one will accelerate more slowly than the first, but that it'll cruise 70 MPH with a more agreeable engine speed.

[EastCoastCB]

Originally Posted by PNW_Steve

It depends on your tire size, engine and desired top speed(or cruising speed).

My Bluebird has 11r22.5 and , 8.3 Cummins and 5.38 rear gears. It goes fast enough in 5th (67+) but is wound up tight. I want 6th to reduce rpm at highway speeds.

If my rear gear was much taller at all I probably would not be looking to unlock 6th.

Personal preference : I think that 65mph is plenty fast in a 26k lb bus. Fuel mileage in my bus drops notably when I run 65mph Vs. 55mph. If I recall, drag increases with the square of speed and overcoming drag is the primary consumer of hp/fuel at highway speeds.

I need a bus that can achieve 70-75 when needed. Won't need it much as I live deep in the "45mph" areas. But one trip through atlanta in a bus made me want one that could at least keep up when NEEDED.
My shorty is more or less capable of 80 with bigger tires on it. As with any school bus- its happiest at 55-60.

[o1marc]

What other trans have an unlockable 6th gear or have a working 5th gear?

[EastCoastCB]

Originally Posted by o1marc

What other trans have an unlockable 6th gear or have a working 5th gear?

I've been told later model 2000-series have a 6th gear. IDK anything about it, but Chris does.

[Twigg]

Originally Posted by EastCoastCB

I've been told later model 2000-series have a 6th gear. IDK anything about it, but Chris does.

They do, but they also need extra hard parts to use 6th, it's not just software.

[PNW_Steve]

I have read a bunch on the 2000 series but have never owned one.

My best understanding is that early versions were 5 speed only and could be upgraded to 6 speed by swapping hard parts & programming. Later models have the hardware and only need the appropriate programming.

[EastCoastCB]

Originally Posted by PNW_Steve

I have read a bunch on the 2000 series but have never owned one.

My best understanding is that early versions were 5 speed only and could be upgraded to 6 speed by swapping hard parts & programming. Later models have the hardware and only need the appropriate programming.

That's what Chris told me, IIRC.

[Panoman14]

Originally Posted by PNW_Steve

I have read a bunch on the 2000 series but have never owned one.

My best understanding is that early versions were 5 speed only and could be upgraded to 6 speed by swapping hard parts & programming. Later models have the hardware and only need the appropriate programming.

If I may quote from the range increase PDF, "All 3000/4000 series transmissions have the ability to achieve 6 speeds; however, only 1000/2000 Series transmissions built after June 28, 2006 contain the necessary hardware to achieve 6 speeds."

I forgot that was in that letter, but I knew I had read it somewhere.

[EastCoastCB]

Originally Posted by Panoman14

If I may quote from the range increase PDF, "All 3000/4000 series transmissions have the ability to achieve 6 speeds; however, only 1000/2000 Series transmissions built after June 28, 2006 contain the necessary hardware to achieve 6 speeds."

I forgot that was in that letter, but I knew I had read it somewhere.

I wonder if the extra gear is the only difference.
If my 2000 ever goes out I'd gladly swap it for an extra OD gear.

[Miles O Roads]

Wondering how hard it would be with mine,dont think they would approve with the gearing. Probably go the secondary tuning programming.

[Mgulley82]

Thomas replied to my request with a “I’m forwarding this to my supervisor” email

Local Allison shop quoted me $175 to program once I have a letter from Thomas

[Miles O Roads]

Originally Posted by Mgulley82

Thomas replied to my request with a “I’m forwarding this to my supervisor” email

Local Allison shop quoted me $175 to program once I have a letter from Thomas

Good stuff. I may submit mine worst they can say is no.

[Mgulley82]

Originally Posted by Miles O Roads

Good stuff. I may submit mine worst they can say is no.

Better sooner than later

I have 2 months before I want to hit the road at this point so I’m in no rush

[Mgulley82]

Thomas informed me it would take several weeks to get approval for the modification request

[Mgulley82]

Received email that my modification order has been sent to engineering

[cadillackid]

Originally Posted by EastCoastCB

I wonder if the extra gear is the only difference.
If my 2000 ever goes out I'd gladly swap it for an extra OD gear.

the gears and clutches exist in the earlier 2000s. but the valve body and associated electronics are differences..


https://www.xtremediesel.com/sun-coa...eed-conversion


-Christopher

[concrete]

I have a 1996 IH 4900 (WHAT!?! On a skoolie forum!? Yes, heresy, I know. But this place has the best info on this subject anywhere I’ve found—By a wide margin.); dt466 250hp HT (mechanical injection), md3060 (close ratio), 5.38 rear, 11R 22.5, lever shifter (I think WTEC 2).
I tried (twice) through the OEM, but IH says they won’t approve anything older than ~2004. Apparently they don’t keep records for stuff that old so the engineers don’t have the numbers they need.
Plan B: get a donor with the same/similar power train and all 6 gears (anybody know of one?). Said donor could supply the TCM itself (assuming it’s a salvage vehicle) OR THE NUMBERS ALLISON USES TO PROGRAM TCM’s. From my research (I haven’t done this yet, so please correct me if you know different) Allison needs 4#’s: vehicle VIN, transmission serial #, TCM/ECU #, and the CIN# (calibration #). With these numbers an Allison dealer will reprogram your TCM to the supplied specs for ~$130-150, according to phone calls I’ve made.
How similar does the power train need to be? I don’t know. Presumably the tranny itself should be identical. Presumably the engine should have the same kind of communication with the tranny (i.e.—mechanical throttle sensor vs electronic style); perhaps dissimilar engines with similar tranny communication could be interchangeable? Rear gears and tire size would presumably affect speedo accuracy, but perhaps would still work well? I’d rather have 6th gear and an incorrect speedo...
Lots of assumptions. I only know my own experience with IH and what I’ve read online; I’m counting on y’all to be my fact checkers. Shout-out to Cadillackid! I have really appreciated your posts on this and other threads. A couple other members as well, but I don’t have their names handy...
If you have the same/similar power train I do, PLEASE contact me ASAP! I bought this truck online, am picking it up today-June 8 (I’ve been trying to post this for a while, but my account wasn’t working correctly) in Ohio, and driving it to Alaska. 6 gears will make for a much happier road trip.
Again, if you have or know of a vehicle with the needed stuff, please let me know! I’m assuming a PM would be the best way to relay the info; though posting it all openly on the forum would be convenient for all interested parties.
LET THE ROAD TRIP BEGIN!! (Hopefully with 6 gears)