HarleyRyder
Retired Gunslinger
Ray-
Mea culpa. When I researched buying my new 3500, I didn't really pay that much attention to the automatics because I did not want one and was only interested in a 6-spd manual.
The Aisin is in fact offered in a 3500 on up cab/chassis configuration with Cummins, but apparently not if you order a pick-up. Interestingly enough the 3500 cab/chassis has the Hemi with 5-spd auto as the base powertrain. Go figure.
If I recall my information on both 6-spd automatics correctly they are both double overdrive just like the 3000 Allisons in motorhomes.
Mea culpa. When I researched buying my new 3500, I didn't really pay that much attention to the automatics because I did not want one and was only interested in a 6-spd manual.
The Aisin is in fact offered in a 3500 on up cab/chassis configuration with Cummins, but apparently not if you order a pick-up. Interestingly enough the 3500 cab/chassis has the Hemi with 5-spd auto as the base powertrain. Go figure.
If I recall my information on both 6-spd automatics correctly they are both double overdrive just like the 3000 Allisons in motorhomes.
cdbMidland
Past Michigan Chapter Leader
To pull a grade, it takes torque from the prime mover. So the best rpm for pulling is at the engines maximum torque point on the torque curve. For the CTD, this point is 2100 to 2200 rpm depending on the fueling curve. This also normally the best point for maximum fuel mileage, if high output is being demanded. Therefore, I normally tow at this rpm or just a little above so I am at maximum torque after the turbo lag clears. With this setup, the only reason I need to down shift is for slow traffic.
I'm curious. My 2006 with the 4-speed auto and 4.10 rear end runs at 1800-1900 towing on a level grade at 60 mph, which I've been told is a good speed for the Bighorn and its Goodyear tires. 2100-2200 rpm would take me to nearly 70, which exceeds the recommended tire speed.
Ray LeTourneau
Senior Member - Past Moderator
To pull a grade, it takes torque from the prime mover. So the best rpm for pulling is at the engines maximum torque point on the torque curve. For the CTD, this point is 2100 to 2200 rpm depending on the fueling curve. This also normally the best point for maximum fuel mileage, if high output is being demanded. Therefore, I normally tow at this rpm or just a little above so I am at maximum torque after the turbo lag clears. With this setup, the only reason I need to down shift is for slow traffic.
The 6.7 makes max torque @1600 rpms. I think the 5.9 was @2100.
dieselengineer
Charter Member
Actually for the CTD 6.7 in stock form the max torque is 650 ft-lbs @ 1500 rpm
Engine ModelAdvertised hp @ rpmPeak Torquelb-ft @ rpmGoverned SpeedCummins 6.7L Turbo Diesel350 @ 3013650 @ 15003013
Torque Curve.
Engine ModelAdvertised hp @ rpmPeak Torquelb-ft @ rpmGoverned SpeedCummins 6.7L Turbo Diesel350 @ 3013650 @ 15003013
Torque Curve.
Ray LeTourneau
Senior Member - Past Moderator
I didn't know it till this morning. We were going down a hill we went up yesterday. Going down, we saw the sign saying 6% grade, truck run off lane ahead. Test brakes and all that. Point is, on the way up this grade yesterday the D'max/Allison went down into 3rd and at 45 mph was running 2500-2600 rpm. We were able to maintain this speed easy enough. If we sped up it would up shift but couldn't maintain speed in 4th. The grade was about 1-1/2 miles long. Truck is stock except for flange back exhaust. Anyone saying their truck would make a 6% grade without downshifting is stretching the truth a bit. I would have to see it to believe it.
I would have to see it to believe it.dieselengineer
Charter Member
My truck does not shift by itself.