Allison Trans Shifting

shanandoah · July 20, 2004

2500HD Diesel, Allison. Between 2nd & 3rd gears, the engine rpm drops about 200 rpm, almost as if it is shifting. More noticable towing heavy loads. Does anyone else have this symptom??

Boosted · July 21, 2004

Are you using the tow haul button? My Allison did something like that when I first got it and has not done it since. I have chipped it so the trans had to go through a learning mode again...

robsawatsky · July 21, 2004

The Allison has torque convertor lock-up through the top 3 gears (or is it even top 4?). Sounds like TC lock-up is what you are experiencing. Lock-up will vary depending upon tow/haul, speed and other conditions.

shanandoah · July 22, 2004

YES, I am using tow-haul mode when towing a trailer. However, this happens when in tow-haul or not, towing a trailer or not. It is just more noticable when towing a heavy load.