Transmission Choices

[Karen333]

We are looking at using a Cascadia chassis with DD13 470 HP engines in our planned Super C conversion. We are still deciding on which manufacturer to go with but now we are trying to figure out the advantages/disadvantages of the tranny. The Allison 4000 series 6 speed vs. the Detroit DT12 (12 speed). I know Allison has a great name but not sure if we need more speeds than what the Allison offers.

[LJowdy]

If an Allison can propel a 40-50K motorhome, then I'd probably go with Allison. So much depends on the tire diameter and ring and pinion combination.

[99phantoms]

To the OP -

I do not own an RV, so I have no 1st hand experience.

But... last month while at the Tampa RV show, I had some lengthy discussions with ShowHauler reps and others about chassis, engine, and transmission combinations. Almost everyone agreed that the Cascadia chassis, DD13 motor, and DT12 transmission is the way to go. They said it's a great combination... smooth shifting, etc.

Folks with Allison experience please chime in, but seems 12 gears would better enable keeping the engine RPM in the desired torque range.

[Bob86ZZ4]

I've had my rig since '09, and put about 60k miles on it. Mine is a 10 speed autoshift. I wouldn't consider a Allison hydraulic transmission. The autoshift type transmissions don't have a torque converter. That to me is the key. Direct connection from input to output, not a fluid connection.

[Steve Ownby]

Originally Posted by Bob86ZZ4

I've had my rig since '09, and put about 60k miles on it. Mine is a 10 speed autoshift. I wouldn't consider a Allison hydraulic transmission. The autoshift type transmissions don't have a torque converter. That to me is the key. Direct connection from input to output, not a fluid connection.

I've never driven an auto shift type but it sounds like a good concept. The Allison 3000/4000 series lock up the torque converter in 2nd gear and it's locked in ever gear above.

[Bob86ZZ4]

Well, I don't know much about the Allisons. I know the auto trans in my van has a locking torque converter and it will un-lock under certain conditions. One other thing. I talked to the service manager at the local Kenworth dealership about these auto-shift type trans. He told me he couldn't remember ever having to take apart one. He said they've done repairs on the external electronics and such, but never had to pull one apart. He said the fleet owners really like them for their durability. I don't know if you'd find the same results with an Allison.

[Mr_D]

My Magna has a 650 HP Cummins with 1950 ft lbs torque from 1100 to 1600 rpm and the Allison 4000 MH trans. Frankly I wish it had a 10 or 12 speed trans just so it would run it the fat part of the power band. Not that I've noticed a lack of power but sometimes it just doesn't pick up speed like I think it should. The rig weighs about 46,500 dry and probably 50,000#'s loaded (yes, I need to weigh it). I pulled into a weigh station last time out figuring it wasn't manned and found it was so I left without getting anything but front axle weight.

[Karen333]

Thanks everyone. My husband had been doing research and likes the DT12

[dtchild1]

If you like the DT 12, you owe it to yourselves to check out the "I-Shift" in the Volvo chassis too. I know Haulmark uses the exclusively in their truck conversions due to a great shift and warranty.

[johndfd]

I don't have any experience with any of the automated manual transmissions that have been mentioned earlier. I have however, put lots of miles on Allison 5 and 6 speeds. I have a Ford Super Duty 1 ton/ 5th wheel, but my experience comes from fire apparatus. My situation is that I transport mostly new, but also some older fire trucks all over the eastern seaboard and the midwest. Most rigs are DD13s and Series 60, but there are a few ISLs. The trucks from my own fire department have been Mack/Allison and Detroit series 60/Allison.

The lightest trucks I operate are about 35,000-40,000 pounds. They will get 9 mpg @ 67mph with a DD13/Allison, which I think is pretty good considering the non aero profile of a typical fire pumper. In my experience of 30 years of fire department duty, and now over the road transport of all types of fire trucks up to 84,000 lbs, the Allison transmissions are bullet proof. Climbing long interstate grades, stop and go traffic, etc, I never see trans temps climb above the norm, which is 190-200 degrees. The Jake brake performance of the DD13/ Allison combo is outstanding also. The lighter pumpers (around 40K lbs) will beat almost any other heavy truck on grades if I am DD13 equipped. When I get above 75,000 lbs in a 10 wheel ladder truck however, I'm not setting any records on hills, but I'm pretty much doing what all the other class 8 trucks are doing, even when I'm running an auto transmission. The heavy ladder truck acceleration is on par with the civilian class 8 trucks also.

Fire fighters are good at 1) putting out fires, 2) breaking things. The Allison is in 98%(or more) of fire trucks regardless of who builds them. I was very leery of them when I first drove one in 1984, but I'm a believer now. A plus for the auto is in stop and go traffic. The torque converter allows one to creep along, with no trans temp increases. The automated manual still has a clutch, which can get hot. I think most automated trans have a "hot clutch" or "clutch abuse" light, not a factor with the Allison. The Allison can easily creep a few inches at slow speed, for hours with no issues. I think the manual automated transmissions skip gears in economy mode, which makes them a 5 or 6 speed, which is the Allison.

Some emergency vehicles have a low rear end ratio for fast acceleration, they run at 2200 rpm at interstate speeds. Those trucks can keep up with most cars leaving a traffic light. If a rear ratio could be higher to allow 1500 rpm (or whatever is best fuel economy), the Allison in top gear would give good mpg, maybe not quite as good as a trans with more ratios, but very good.

I don't think you will be going wrong either way... Good choice to have a diesel engine in front of you, most helpful to fix, and if involved in a crash.

Good luck!

[dadej]

You should consider a volvo with the ishift. I have had three motorhomes with six speed allison. Good but more gears would be nice. I had a m-2 freightliner pulling a 10000 pound fifthwheel, 300 hp cat and eaton 10 speed ultra shift. Nice transmission but jerky when backing up to the fifth. Now I have a 2014 volvo ishift pulling a 19000 pound fifth. No jerking when backing up and no downshifting when pulling hills. Quieter interior then my 2000 ford PSD. I would drive one of each before I would spend that much money. Just a thought.

[oldgrizz]

As a fleet manager and mechanic of heavy trucks I give a very big plus 1 thumbs up for the Volvo I shift.
We had them in our fleet and the drivers really loved them. We used the 13 liter and I shift combination.
The beauty of these units is that both the engine and transmission are built by Volvo. The I shift was built as an automatic and is not some 12 speed manual that has has solenoids added to make it an automatic.
The drivers said that the combination of the engine and I shift also had better hold back on hills than the Cummins and engine brake.
We also had no failures and the loads were at times 90000lbs.

[grassy]

I like my Ultrashift. It feels like a an autoshifting manual. Sounds cool too..
You can also run in Manual or low mode. When I am bobtailing.. I start off in 2nd or 3rd.

My dw would not pilot a manual with the rig attached..

Eaton is an excellent company.