Allison 2500MH- 5 or 6 speed?

[Mattera68]

I just got home with my 2005 Cross Country, I found the plate on the trans to tell me its a 2500, because I noticed it only going to D5. After looking on the Allison website, they show gear ratios for 6 gears. Do some have 5 and some have 6? This is my first diesel and I was told that it sounded like it was running kind of high RPM's coming home.

Thanks for any help,
Tony

[Mr_D]

Some were 5 speeds and some are 6 speed. As I understand it the 5 speed is actually a 6 speed with the top overdrive locked out due to the rear end ratio not being right to pull 6th. But that's just from Internet sites so I don't really know.

[Cat320]

Next time you are on the road, as you accelerate, watch the tach and count the number of shifts.

[srydve]

If you remain unsure copy the serial number down and call Allison 1-800-524-2303

[allisontec]

6 speed models didn't come out until 06 or 07.six speed models have a different valve body and tcm calibration.The 3000/4000 series are the ones that can be 5 or 6 speeds according to the calibration in the computer.

[Mr_D]

Quote:

Originally Posted by allisontec The 3000/4000 series are the ones that can be 5 or 6 speeds according to the calibration in the computer.

I've never heard of or seen a 3000/4000 that wasn't 6 speed in a motorhome.
Other sites say some of the 2500's could be changed from a 5 speed to a 6 speed by a simple reprogramming but it wasn't recommended due to the rear axle ratio.

[Wayne M]

My 2008 (built 2007) ISB 6.7 340 hp runs with the Allison 2500 and has all 6 speeds.

[FleetMan]

Wayne M,
Just out of curiosity, what is the rear end ratio on your coach? My 07 Journey, built Nov, 06 with ISB-02, MH 2500 5 speed, has a 4.78.1 rear. Not considering engine torque, a double overdrive, unless the 5 to 6 step was very small, would put me at speeds far in excess of what I would normally drive. My peak torque is at 1600 RPM, 62 to 65 MPH is in the 1950 to 2100 RPM range.