Allison vs Detroit Transmission Cascadia

[Valor1]

Would someone share with me their understanding of pros and cons for Allison vs Detroit transmissions in the newer, big RV applications like the Cascadia chassis? I'm referring to the Allison, 6 speed, true automatic and the Detroit, 12 speed, automated shift manual transmissions. My research indicates that the Detroit may be a better choice for running up and down the highway, particularly when climbing a grade, but that Allison may be better at slow speed maneuvers such as backing up on a trailer. I'm sure there's a tradeoff, so what does one sacrifice with one over the other?

[KFed 90-10]

I have the Eaton 13 speed ultra auto shift and a Cummins ISX15. I have not driven the Allison 6 speeds. What I can say is the 13 speed is a bit slow to get going from a dead stop. All those gears to shift thru. It usually starts in 2nd, and skips a few gears along the way to about 60 mph where it shifts into 13. It really doesn't get going until you hit 8th or 9th gear. As far as slow speed maneuvering, like in a campground, I can select low, and it starts out in 1st, making it very easy for slow speed maneuvering, whether going forward or reverse . Where it really shines is going down the highway and especially up and down hills where you can always use the paddle shifter and be in the rpm sweet spot for power and torque. It has no problem charging up hills in 11th or 12th gear keeping the rpms at or above 1500. Lugging the engine is never an issue. Because I'm in the Mountain west, I really like having all the gears at my disposal for climbing and especially engine braking going down hill.

[Valor1]

KFed, thanks for sharing your experience. It seems like the extra gears could definitely make it easier to keep engine RPM in the power band. A strong plus for having the extra gears. I wonder if people who run the Allison up and down the highway and particularly in the mountains find their engine RPMs being too high or too low, depending on the situation.

[DeetsMaggie]

Have never driven coach with the DT12, but have driven many miles with the Allison 6 speed. My opinion is that the Allison is fine on flat highway and interstate, towing or not towing, all is good. But Allison is completely unsuited for the mountains and hills found in the intermountain west. After experiencing it one can only conclude that the Allison was not designed for mountains. Its performance on mountain grades is quite poor. The Allison/ISL9 combo found in Renegades' Veronas and elsewhere was intended for local delivery trucks delivering lumber, concrete, brick and the like to the local hardware stores. Or perhaps very short haul regional service. Never intended for "Over the Highway" use.

Still, it always gets us where we are going.

If we ever purchase again, it would be a chassis with either DD13/DT12, or DD15/DT12 combo, depending on length and weight of the coach.

Happy travels.

DeetsMaggie

[Uncle_Mike]

Originally Posted by Valor1

I wonder if people who run the Allison up and down the highway and particularly in the mountains find their engine RPMs being too high or too low, depending on the situation.

Valor1, that is one thing I've heard from the Classic+Allison owners: the transmission does seem to "hunt" a lot for the right gear because they are spaced relatively widely. Some have said that because the Allison was intended for local/regional work, the gear range is biased lower than it would be for OTR use. But I don't know if that's true.

Another thing to consider is cost. On Cascadia-based Classics at least, the DT12 is standard and the Allison is an option. From what I can tell by comparing build sheets, the Allison 4000 is about a $7-8K upcharge. That almost pays for the Aqua-Hot!

[wolfe10]

Originally Posted by DeetsMaggie

. My opinion is that the Allison is fine on flat highway and interstate, towing or not towing, all is good. But Allison is completely unsuited for the mountains and hills found in the intermountain west.

DeetsMaggie

What do you find that makes you say that the Allison 6 speed "completely unsuited for the mountains ..."?

[Valor1]

Deets and UncleMike, thanks for sharing your experience. I didn't realize the DT is standard equipment and Allison an optional upgrade... There seems to be a lot of Classics out there that get spec'd with the Allison by the dealers. But I can't figure out an obvious advantage to optioning the Allison, particularly if the DT operates smoothly in lower speeds/gears. Maybe it's as simple as some people find comfort in the Allison shifting a lot like the transmission in their normal vehicle? I don't know, but thanks for your input!

[Rumline]

Originally Posted by Uncle_Mike

Some have said that because the Allison was intended for local/regional work, the gear range is biased lower than it would be for OTR use. But I don't know if that's true.

Since the Allison only has 6 gears, yeah, it's not that ideal, especially ascending or descending steep grades. But "biased low" is not true in my experience. My Valencia only has the 2500 transmission, not the heavier 3200 on the Veronas so this may not equate 100%, but it won't even shift into 6th gear until 66+ mph even with "mode" off (meaning economy program active). I rarely drive above that speed so I rarely ever see 6th gear. When I made a trip across Wyoming recently and speed limits were posted at 80 mph I did go up to 72-75 for a bit and finally got to use my 6th gear for extended periods. The rig had plenty of power even at those speeds for pulling hills etc although I did let it slow 3-4 mph going uphill.

It does do well "in the city." Off the line it's very slow until the turbo finally spools at ~1600 rpm which can be agonizing. But after that I can keep up with cars etc and it reminds me of a pickup truck shift program.

In my admittedly limited experience with my Valencia, I have been pretty satisfied with the performance of the transmission, other than wishing it had just two more gears at times. It does a good job of selecting the right gear for the situation, especially with "mode" enabled ("performance" program active). I only have to manually adjust it when going down steep grades, (5% or more) and that could be because I don't have a real engine brake.

Anyway I just wanted to add my 2c that even in the mountain west, (I live in Colorado) the Allison is OK. I'm sure the DT's are better. But don't feel like you're going to be limping along at 20 mph and 3000 rpm just because you didn't get the big boy transmission. If I had the money to commission a new Classic I'd be looking pretty hard at the DT though!

[Idleup]

Originally Posted by DeetsMaggie

Have never driven coach with the DT12, but have driven many miles with the Allison 6 speed. My opinion is that the Allison is fine on flat highway and interstate, towing or not towing, all is good. But Allison is completely unsuited for the mountains and hills found in the intermountain west. After experiencing it one can only conclude that the Allison was not designed for mountains. Its performance on mountain grades is quite poor. The Allison/ISL9 combo found in Renegades' Veronas and elsewhere was intended for local delivery trucks delivering lumber, concrete, brick and the like to the local hardware stores. Or perhaps very short haul regional service. Never intended for "Over the Highway" use.

Still, it always gets us where we are going.

If we ever purchase again, it would be a chassis with either DD13/DT12, or DD15/DT12 combo, depending on length and weight of the coach.

Happy travels.

DeetsMaggie

I respectively disagree, an Allison 6 speed will climb any mountain a 12 speed will provide you have the engine in front of it. I’ve driven 6 speed transmissions in big rig coaches all over the US never seen a mountain yet that I can’t climb.

The biggest problem with Allison transmissions is most owners throw a car behind the RV put it in drive and go tackle mountains. Most don’t realize that an Allison is really a 4 speed transmission with two overdrive gears. For this reason at times you have to shift it manually. Another important point is RV gear ratios are designed for mileage and not for pulling big weight.

While you certainly have a better selection of gears with a 12 speed, its the engine that determines just how aggressive it can climb a hill. For the most part 12 speeds is over-kill fo any RV, 12 speed transmissions are designed for over the road use pulling 70-80,000 pounds. With the Light weight of our RV’s there is no need for a 12 speed transmission, which is the precise reason nearly every RV is equipped wit 6 speed Allison.

Best Regards Mike

[jcussen]

Originally Posted by Idleup

I respectively disagree, an Alison 6 speed will climb any mountain a 12 speed will provide you have the engine in front of it. I’ve driven 6 speed transmissions in big rig coaches all over the US never seen a mountain yet that I can’t climb.

While you certainly have a better selection of gears with a 12 speed, its the engine that determines just how aggressive it can climb a hill. For the most part 12 speeds is over-kill fo any RV, 12 speed transmissions are designed for over the road use pulling 70-80,000 pounds. With the Light weight of our RV’s there is no need for a 12 speed transmission, which is the precise reason nearly every RV is equipped wit 6 speed Alisons.

Best Regards Mike

Agree, with the 6 speed , you just need to select the gear you need, you have the right ratio for almost any situation.

[petrel]

Glad this topic was brought up. I've been wondering the same thing.

My Renegade is equipped with a ZF 12 speed automated. For the most part, it thinks it is a 5 or 6 speed. It usually rolls off in 3rd and skips its way up to 12 pretty quickly.

We recently spent some time in the Mtns. of VA negotiating some 7, 8, and 9% grades. The rig definitely rediscovered those other gears it hadn't been using recently, which was especially nice for braking on the way down.

I seldom operate it in manual mode, except occasionally putting it into 1st gear when maneuvering in my driveway. I figure the engineers at Detroit Diesel and ZF decided when the thing should shift. I'm not second guessing them. I just set the cruise control and let it figure it out.

[lslblues]

Your Valencia should have the 3000MH transmission. The Verona's have the TRV3200. My Valencia will shift into 6th gear at 55 MPH when not in Mode, and at 72 when in Mode.

Its like everything - pros and cons to every options and it depends on your specific use which is optimal. I live in the SE and am very happy with ISB/3000 combo. Probably wouldn't be as happy if I lived in Colorado.

Originally Posted by Rumline

Since the Allison only has 6 gears, yeah, it's not that ideal, especially ascending or descending steep grades. But "biased low" is not true in my experience. My Valencia only has the 2500 transmission, not the heavier 3200 on the Veronas so this may not equate 100%, but it won't even shift into 6th gear until 66+ mph even with "mode" off (meaning economy program active). I rarely drive above that speed so I rarely ever see 6th gear. When I made a trip across Wyoming recently and speed limits were posted at 80 mph I did go up to 72-75 for a bit and finally got to use my 6th gear for extended periods. The rig had plenty of power even at those speeds for pulling hills etc although I did let it slow 3-4 mph going uphill.

It does do well "in the city." Off the line it's very slow until the turbo finally spools at ~1600 rpm which can be agonizing. But after that I can keep up with cars etc and it reminds me of a pickup truck shift program.

In my admittedly limited experience with my Valencia, I have been pretty satisfied with the performance of the transmission, other than wishing it had just two more gears at times. It does a good job of selecting the right gear for the situation, especially with "mode" enabled ("performance" program active). I only have to manually adjust it when going down steep grades, (5% or more) and that could be because I don't have a real engine brake.

Anyway I just wanted to add my 2c that even in the mountain west, (I live in Colorado) the Allison is OK. I'm sure the DT's are better. But don't feel like you're going to be limping along at 20 mph and 3000 rpm just because you didn't get the big boy transmission. If I had the money to commission a new Classic I'd be looking pretty hard at the DT though!

[DeetsMaggie]

Wolf10,

Regarding....."completely unsuited for the mountains ..."

It would have been better had I written..."completely unsuited for the mountains in Automatic mode...."

I find the Allison must be put in Manual Mode on grades. I believe this is a transmission issue only and I'm not attributing this performance issue to the engine HP and torque. Said another way, it's not that the coach cannot top steep grades at 65 MPH. I don't expect it to. On grade and in Automatic mode, the transmission cannot find and keep itself in the right gear. Doesn't matter where cruise control is set. I expect this is because the ratios for each gear are simply too far apart.

On grades, the Allison is best operated manually. I think it's performing as designed, it just isn't the optimal design for this type of service.

DeetsMaggie

[wolfe10]

Originally Posted by DeetsMaggie

On grades, the Allison is best operated manually. I think it's performing as designed, it just isn't the optimal design for this type of service.

DeetsMaggie

I completely AGREE with you. Same as in my "automatic" car, in the mountains (spent this summer in Angel Fire NM with LOTS of steep grades in all directions), I, not it choose the correct gear. Were it not for the up/down arrows that are so easy to use, I would agree that it is not ideal.


No automatic transmission (left in D) can do nearly as good a job as a smart driver. Transmissions are REactive. Smart drivers can be PROactive-- seeing what is happening in front of them, not hundreds of yards behind them.



And, there is no transmission that will not end up "hunting" on some grade. The smart driver just down arrows to the lower gear and continues on until grade abates.


I like the Allison 6 speeds because they CAN be driven as a manual transmission or on less challenging terrain in "D".