Shifting issues

[JohnDolyn]

Has anyone had a issue with the 2500 Allison not downshifting while under heavy throttle? I just returned from the Rockies, and experienced half a dozen cases where my shift panel would drop from d5 to d4, my tach would jump to 2400 RPM, then slowly drop to 1600-1800 RPM. My Cummings 300 would lug down until I could hit the down arrow to D3, at which time the trans downshifted and I was able to clime the grade. This has NOT happened since I returned East of South Dakota. Any ideas or comments would be helpful as I can not even guess who to have this checked by.

thanks, John

[Diplomat Don]

John...It sounds a little strange. I know that if you have it in "Economy Mode" on a grade it will take it a little longer to drop a gear. The Economy mode is good for rolling hills, but not for a grade.

[radams]

Quote:

Originally Posted by JohnDolyn Has anyone had a issue with the 2500 Allison not downshifting while under heavy throttle? I just returned from the Rockies, and experienced half a dozen cases where my shift panel would drop from d5 to d4, my tach would jump to 2400 RPM, then slowly drop to 1600-1800 RPM. My Cummings 300 would lug down until I could hit the down arrow to D3, at which time the trans downshifted and I was able to clime the grade. This has NOT happened since I returned East of South Dakota. Any ideas or comments would be helpful as I can not even guess who to have this checked by. thanks, John

I've never been able to figure out how to let the Allison do it's thing while going through the mountains either. A wily old truck driver told me once that in the mountains you need to shift with the tach. In other words, he said, keep your RPMS where you need them to be to get maximum torque when going up. Doing that should also keep your coolant and transmission temps in line. Whatever the lowest gear was that you needed to go up is the same one you should be using going down. Take your time he said.

So I keep an eye on the tach, punch the buttons, and I don't think "Alice" minds my help at all. I doubt there is anything wrong with your transmission.

[chev]

The allison transmission has some quirks in it you need to know about. We had a 1999 Beaver Marquis, C12 cat motor and allison trans. Coming down out of the mountains into Ennis, Montana we experienced some teeth rattling down shifts. I mean "BANG"..I experienced it several times. When we left Ennis we scheduled with Allison in Billings and were enroute there. Stopped at a rest stop, and two Marquis owners pulled in, on their way home from Alaska. Told them my problem, they both advised "save your $ they cannot fix it, we both tried". The allison shifts into the next gear up in two stages, if you are in traffic and in "drive" and you speed up to about 30mph it shifts into 3rd, but never quite locks, and when you slow down it slams back into 2nd. This also happened when it shifted into 4th, and I slowed down. The trick is to manually shift when you are in traffic so the transmission doesnt make these decisions all by its self. also, while climbing I always manually shift to keep the RPM's up. This helps the motor and transmission keep the temperature down., Grunting up a hill in 6th gear builds up incredible heat. I usually watch my torque, rather than rpm's. Hope this helps, but dont buy into Allison telling you they can tweek the settings on the trans, it just doesnt change anything.

[walt2137]

John you might want to reboot the Allison trans by removing the battery cables off of your battery and leave it off for a while.

[Robi.1014]

Walt...
A quick "sanity check" please: Removing DC power from the Allison tranny can also be achieved by turning the chassis battery switch to the OFF position?