Allison transmission up-shifting

[wagonmaster2]

On my Chev PU, Honda Accord, and Jeep Wrangler, after coasting downhill in a low gear then manually shifting into a higher gear when the road levels out the transmissions will upshift immediately while still coasting (no throttle applied). But on my Allison 3000 transmission it won't upshift after manually using the touchpad to shift to a higher gear until the throttle is pressed.

Why doesn't the Allison upshift immediately when the touchpad is used to go to a higher gear? No problems, just curious why Allisons work different from other trannys.

Wagonmaster2

[Romeo]

I will be watching for answers because I have a similiar situation with my Allison 3000.

When I use the exhaust brake going down a grade (foot pedal actuated), the trasmission shifts down... when I reach end of the grade and the road levels out and I release the exhaust brake foot pedal, the transmission does not up shift right away. I have also tried pushing the up-shift button on the touch pad, but it appears that I need to accelerate in order for the transmission to up shift.

[wagonmaster2]

Exactly, I think you explained it a little clearer than I did. Must not be any problem with the tranny but I always hate to be giving the engine the gas (diesel) when I'm going down hill slightly anyway. Watching the tach I have to accelerate some so it will up-shift and keep the RPMs from climbing too much in the lower gear.

Wagonmaster2

[Mike Canter]

My guess is that the Allison logic keeps in in the lower gear to aid in deacceleration going down hill so it does not upshift everytime you let go of the exhaust brake. This way the motor aids in keeping the MH slowed down while going down hill if the grade lets off a little. That seems like a good idea to me. Normally the Allison tranny is reprogrammed when an exhaust brake is added. My diesel with the Jake brake does the same thing. When I take my foot off the Jake pedal the transmission stays in the lower gear so the MH doesn't start building up speed too fast.