Peterbilt Automatic Allison Transmission Information Please?

The transmission will only hold gear from upshift not down shift

so changing ranges in my aux requires the Allison to hold both up and down - while the aux changes range (like shifting and 18 spd between hi and lo). When climbing a hill (when one would shift into u see drive in the aux ie more gear) the slowing of the Allison will make it try to shift when the other box is not done. This then gets both out of gear and you have to come to a complete stop - put aux in the old range then the Allison in neutral then go. This is a bad situation to say the least

 

Is your box still programmed in standard factory spec? In that spec correct, you can't lock it in a gear either up or down as the programming uses revs and box speed too change gear. It makes them virtually impossible to destroy.

I got it reprogrammed to "open" (for want of a batter description), at an Alison service agent. So when left in D it will behave like an auto but will no longer seek the lowest gear when exhaust brake is on.
Or I can drop it out of D and drive it like a manual using the up and down arrows on the control display. It will hold any gear increasing or slowing speed, exhaust brake on or off. If I happen to forget I am driving it like a manual, and I slow in 3rd for example, and keep slowing to the point the box may over torque the gear and harm itself, it will change down. But this like under 1000rpm in 3rd. Is that that is what your Aux box is doing? Maybe the Alison attempting to avoid damage? Could that be an Aux issue more than Alison?

I'd chat to a service agent. I was whinging to them one day about wouldn't it to be great if the box did......and they provided what solutions were possible. Happy days thereafter.

 

mine has been to the Allison guys several times and has had the shift points modified to allow near max rpm before up shift- we th my weights I need to stay north of 1500 rpm or it falls flat

I can lock upshift with the arrow but not down shift

 

hmmm......I got nothing mate. Maybe a different box for different weights? You would exect they all have similar programming.