Looking to order T880 Need some imput on Tranny-Engine options

How Fast do you want to go & How much fuel millage do you expect..?

The Heavier the truck The Harder the Pull Use 4.11,4.33,4.44 rears with a 13,15,18 speed trans The Heavier the truck The Higher the Numbers=Pulling good
Pulling Good = Slower Speed on Hwy (Flats)
ISX VS MX13? For Me ISX (been in business Longer)

Autoshift Plus VS Automatic.?? Did you Mean Ultra Shift..?or Regular Trans?

 

Guy who works with me where we o/o out of has a new MX Paccar in his Pete and says it is the worst thing he has ever owned - no power and now out of warranty he is afraid it is literally going to end him. Dealer should be standing up at the plate with him too but is not.

 

I'm a big fan of the MX, it is a 13 liter engine and the ISX a 15. So I think the ISX would fit your weight requirements better, larger engine has to work less to achieve the goal. As far as transmission, spec a ultrashift plus 18spd you will not regret it. I was just taken to the Eaton test track by a local Kenworth dealer and drove ultra shift plus in everything from a 145,000# steel hauler to a 61,000# off road tandem dump truck off road on 26% grades, I'm blown away by it's performance. The 145,000# steal load they had us stop on a 15% grade uphill and start, no roll back and skipped gears going up, then 8% down the other side and grabbed gears perfect. Takes the guess work out of drivers and fuel economy.

 

Allison are "true autos" the ultra-shift plus literally a proven platform FRO manual transmission (8LL9,10,13,18spd) with a computer that shifts and controls the clutch. The MX 500 rating are literally new late this summer, I wouldn't think there is a lot of feedback just yet. It is the exact same engine as the lower horse ratings. The MX is a fantastic engine design from a engineering stand point, but if your wanting to tune the engine I'd say your not going to get that done.

 

Do you know what programming option they had in that 18 speed Ultra+? I'm picking up my new truck tomorrow (Pete 579, ISX 550/2050 w/ 18MXP Ultra+ and 3.08's. Eaton tells me they have no "low-rpm progressive shift" programming for that model. They say if not happy w/ factory programming they can program in what they call a fuel economy program but it's still not a progressive shift like they can install in a 10 or 13 speed. Truck w/ be used on highway w/ reefer coast to coast. I'm hoping for some decent fuel economy, but may have to shift the tranny manually to get it if it won't let you pull down to near the torque peak and wants to over rev before up-shifting. I wouldn't think it would ever need to spin over 1400 -1500 rpms or so w/ that kind of torque and close ratio splits. Hoping to see good economy at about 1250 rpm cruise (65 mph) w/ full fairings on tractor & trailer, gross weights from about 65 to 80K.

 

Forgot about the guy with a new Kenworth. Bought it in Feb. and by May had been on the hook 5 times. Kenworth dealer paid his hotels, rental unit, and any loss of income. Obviously the Kenworth dealer 20 miles away cares more than the Peterbilt dealer in town. I guess it was all electronic issues that would shut the truck down but nothing ever really wrong.

 

They are machines and new technology they are going to have issues sometimes, if your hauling legal highway load 3.08's are the right choice. The new engines like to be lugged down to 900-1000rpm before grabbing a gear. I think you will see good fuel economy. The thing to remember is that just because it's shifting itself don't drive it like a allison. Meaning don't put your foot to the floor on the accelerator, just ease into it and let the truck do the work that it was built for. I think if you do that and keep it at 1250 you will see great results.

 

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