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No D button on dash

Yahoo Message Number: 15870
Sorry for stupid question but I've looked thru the manual and cannot find an answer. What exactly is the no D botton for on the dash of the C5500 Duramax Allison? Is seems to act like trailer mode on later versions. If pulling a trailer should I engage this switch? Should I engage this switch when climbing hills to increase the RPM?

Re: No D button on dash

Reply #2 –
Yahoo Message Number: 15872
Get that, but when should OD be turned off? When pulling a trailer? What does the manual recommend?

Re: No D button on dash

Reply #3 –
Yahoo Message Number: 15873
You should turn off OD when transmission is continually shifting in and out of OD. I also turn off OD iwhen climbing hills and when using cruise control. This stops down shifting after loosing 5 mph then trying to regain that speed while climbing a hill.
Best
Ron Hall

Re: No D button on dash

Reply #4 –
Yahoo Message Number: 15874
Talked to a local truck repair shop. He told be that it helps under 45 to keep it out of overdrive because RPM might shift in and out resulting in very low RPMs which will shift out as soon as you push the accelerator. He also confirmed that on hills under 65. He also added that it could help with breaking in combination with and without the engine break when on downgrades by being in a lower gear. But he added he has never seen a problem with the Allison transmissions and saw no problem leaving it in overdrive even when pulling a trailer.