Detroit DT12 Verses Allison 4000 8 Speeds - Mike Mas

[Idleup]

Detroit DT12 Verses Allison 4000 - Mike Mas

Hello IRV2 Renegade Users - Detroit DT12 Verses an Allison TRV4000! A is a major decision when ordering a Cascadia Renegade or Showhauler or other is deciding between a Detroit DT12 or an Allison TRV4000.
This report will assist owners in making a more informed decision. I'll provide in-depth internal comparisons of the DT12 and Allison to disclose their advantages and disadvantages when used in a motorhome environment. You’ll even see a drag race video of two Explorers one with a DT12 and the other with a Allison and it’s not even close !

Allison’s TRV 4000 “8 Speeds” - No, it’s not a typo or spelling error, Allison's 4000, 3200, 3000 & 2500's are actually 8 speed transmissions. For the first time in the RV industry, I’ll disclose my 2017 findings when I discovered my Newmar New Aire's Allison transmission had two extra speeds for a total of 8 speeds, just as my Verona and new 2025 Renegade Explorer have as well. In this review, I'll outline exactly how owners can obtain extra speeds. I also produced a video of my Explorer shifting twice in 1st and 2nd gears as well as shifting 4 times in 1st & 2nd gears for a total of 8 speeds.

Please Click the link below Enjoy - Mike

https://www.rotory.com/coach/dt12allison5f/

[MemByTheMile]

We have the Allison 4000 and have always wondered about the DT12 and if it would perform better while pulling at highway speeds in mountain areas (fully loaded with our trailer we typically weigh in around 60k).
From other reading and from what you shared here it seems that the DT12 wouldn’t really help where I want the help, to maintain optimum power band for speeds from 50-60.
In our rig if we hit a good grade while doing 60 mph we will definitely slow down until the Allison downshifts to gear 5, at which point we hit a better part of the power band and can maintain speed.
Or if we hit the grade slightly faster at 65-67, we are in a sweeter spot in the power band and can usually maintain that speed.
Doesn’t sound like the DT12 provides extra gear ratios for slower speeds and not higher speeds.
Thanks for your write ups, enjoy reading them.

[Idleup]

By the Mile thanks for the reply - You pretty much have it figured out. Most of DT12’s gearing is in lower speeds, generally at only 35 mph, I’m in 6th or 7th gear. The way Allison gets away without extra top end gearing at “Road Speeds”, is 5th and 6th gear are “Overdrive” gears rather than actual gear change ratios. This allows an owner to drop one or even two gears to get a bite on an upcoming hill without over-speeding our low turning larger diesel engines.

Certainly I’m not implying that a DT12 is an inferior transmission to an Allison, only the fact that 12 speeds is redundant for chassis loads of 40-50K pounds. No one is actually drag racing their coaches and once a DT12 or Allison is moving, there is little to no loss of performance or economy with either transmission.

Myself, I would have no problem ordering a coach with either transmission, since my Allison is in manual mode more than automatic. Personally, I like controlling my own shifts. As I mentioned, in the article, Allison shift schedules are more in tune to fuel savings, rather than performance, this is why Allison now has a number of “Fuel Sense” shift protocols, which bog down and over-shift to keep RPM far to low for motorhomes like a Renegade or Showhauler.

Regards - Mike

[SafariBen]

No matter how many times you say it, an Allison six speed does not have eight speeds. Hundreds of millions of automatic transmissions are out there that lock up the torque converter a few seconds after the shift to make use of the torque converter, but not burn the fluid. Nobody calls them any more speeds than they are besides you.

[lslblues]

Moot point now for new purchases. No more Cascadias with Allison. All DT12 for now.

[Idleup]

Originally Posted by SafariBen

No matter how many times you say it, an Allison six speed does not have eight speeds. Hundreds of millions of automatic transmissions are out there that lock up the torque converter a few seconds after the shift to make use of the torque converter, but not burn the fluid. Nobody calls them any more speeds than they are besides you.

Yes, everyone does know that torque converters lock up, in fact every automatic transmission made for cars, trucks and even RV's, use lockup for fuel savings.

Every Allison owner knows an Allison produces 6 speeds in Automatic mode, but what they "didn't know" was an Allison can produce 8 speeds in Manual, or at least no one that I know of, except for the owners I shared my findings with, which now use manual exclusively loaded.

Using manual with the two extra speeds loaded, knocks off 8-10 seconds 0-60 mph compared to using auto and just stepping on the throttle.

Watch the video again, the rpm, mph, gear display, listen to it shift and you'll see and hear four distinct separate speeds in 1st & 2nd. Try it, you be back here thanking me!

Regards Mike

[SafariBen]

Brett and I know that they lock up after the shift, just like hundreds of millions of other automatics. Our 90's Allisons do that all the time, not sure what you think is new. I've noticed it in newer Allisons, so I'm not sure what the difference is. I'm not watching your video and not thanking you for your revelation.



As mentioned, Allison introduced lock up clutches in 90's, most autos introduced them around the 80's as far as I remember, so no, not all auto trans made have lock up clutches. The 545 was made until 2003 without lock up torque converter. The lock up was as much to prolong life through cooler temps as for fuel savings.

[truckin-on]

Thanks for this review/posting - appreciated! Although I disagree that the Allison's an 8-speed, your explanation of the torque converter's role in getting things moving is spot-on and important to understand relative to the DT12 "SMG" gearbox. SMG = 'Sequential Manual Gearbox' which is what the DT12 actually is. The other point you made - that above a certain speed, the DT12 and the Allison are both "done" with respect to choices at 60-70MPH is also interesting. I suspect there isn't enough of a market to make a re-geared DT12 that would be more appropriate for a lighter Super-C. In any event, well written and good information - thanks!

[d23haynes57]

Many folks will really appreciate the manual forcing of the torque converter to lock up under load when that torque converter lock up clutch gets burned up or worn out. If this is really of benefit you are overloading it or expecting too much. Being a bit of a cheapskate I prefer to extend the life of my equipment and I have some faith that the folks that design and program these things know a hell of a lot more than me, so automatic operation it is except for extreme conditions where safety is also concerned, that is if needed to control speed downhill or maintain control on slippery road surfaces.

[d23haynes57]

The Allison or DT-12 is not what needs to be regeared. The rear axle ratio is.

[Uncle_Mike]

Originally Posted by truckin-on

Thanks for this review/posting - appreciated! Although I disagree that the Allison's an 8-speed, your explanation of the torque converter's role in getting things moving is spot-on and important to understand relative to the DT12 "SMG" gearbox. SMG = 'Sequential Manual Gearbox' which is what the DT12 actually is. The other point you made - that above a certain speed, the DT12 and the Allison are both "done" with respect to choices at 60-70MPH is also interesting. I suspect there isn't enough of a market to make a re-geared DT12 that would be more appropriate for a lighter Super-C. In any event, well written and good information - thanks!

I don't understand your point about the DT-12 being sequential. What do you mean?

Also, Detroit offers the DT-12 with many different gear sets for different applications, but Renegade only orders one. Same for rear diffs. The only way a Renegade buyer can choose is to custom-order their own chassis, and even then their choices will be subject to review and approval by Freightliner engineering. Ask me how I know.

[KFed 90-10]

Zero to sixty??? Who really cares in an RV. I might only start up a couple of times a day from a dead start. But accelerating from 50 to 70 happens many times a day. This is where the 12 speed or in my case a 13 speed really shines. I'm never out of the RPM power band. Climb a hill? Descend a hill? Toggle down a gear or two, to maintain virtually any speed. I don't tow a heavy load, but those who do, need those close ratio gears!

[lslblues]

Final gear ratios for the DT12 and Allison are such that 2nd gear locked up is identical to 8th on the DT12. I’m in 2nd gear at 22 mph. So I have 2-6 or 5 gears to drive between 22 and 85. DT 12 has 8-12 or 5 gears to drive between 22 and 85. The difference is just the gear spacing. Our 6th is taller than 12th, and our 5th is between 11th and 12th. I do like the gear spacing better on DT12.

[Idleup]

Originally Posted by d23haynes57

Many folks will really appreciate the manual forcing of the torque converter to lock up under load when that torque converter lock up clutch gets burned up or worn out. If this is really of benefit you are overloading it or expecting too much. Being a bit of a cheapskate I prefer to extend the life of my equipment and I have some faith that the folks that design and program these things know a hell of a lot more than me, so automatic operation it is except for extreme conditions where safety is also concerned, that is if needed to control speed downhill or maintain control on slippery road surfaces.

Thanks for the reply - Regretfully, there is nothing we can do as drivers to change the lock, slipping or shifting of the Allison when using Drive. The control module keeps tab of what the chassis is doing and makes decision on gear change and the torque converter locking and unlocking. Regardless if you are in Drive or Manual, your Allison will always slip on launch in 1st and 2nd gears, to keep the transition smooth. Therefore, don't worry about using manual its safe.

When using Manual, it allows the driver to make a wider shifts for performance, it also spreads the slip and lock times (extra speeds) as well. When I pulling a heavy load, my 0-60 mph is 8-10 seconds shorter using manual verses Drive.

When we use Drive, we’re at the mercy of the TCM, so it crams in the gears way to early almost bogging the engine. Freightliner programs the Allison to do this save fuel. Fuel efficient trucks is the #1 selling feature trucking companies look for. Even 1mpg difference means a lot, for a semi running 18-24 hours a day for 28 days a month. Therefore, Freightliner deliberately turns the diesel engine “Slow” for two reasons. An engines that turn slow, consume less fuel and secondly for engine drag (less fuel also). An engine turning 2000 rpm has twice the drag of an engine turning 1000 rpm. It consumes considerable power to turn the big engines, crankshaft, pistons, camshaft, fan, pumps, compressors and the massive transmission torque converter.

Regards - Mike